u.s. navy ferro- cement boat building manual volume 2

NAVSHIPS 0982-019-1010

U.S. NAVY

FERRO-CEMENTBOAT BUILDING MANUAL

VOLUME II

NAVAL SHIP SYSTEMS COMMAND

WASHINGTON, D. C.

1972

This document has been approved forr public release and sale: Its distribution is unlimited.

http://www.boatdesign.net/ferro/

FOREWORD VOLUME II

FOREWORD

This volume of the Ferro-Cement Boat-Building Manual covers plastering tools andtheir use, preparation for plastering, plastering, steam curing and hull repair. It has beenassembled to give guidance to the people planning and organizing a boat-building projectand to the men physically doing the work.

Applying the mortar to a ferro-cement hull is hard work. The chemical action ofsetting cement waits for no man. The people undertaking this strenuous and exactingjob must work hard and fast to properly apply the mortar to a hull. The mortar mustthoroughly penetrate the mesh, and be smoothly finished both inside and out or all thegood work preceding plastering can be destroyed.

Plastering is an extremely crftical stage of boat-building but the most rewarding.All that precedes plastering and follows is overshadowed by the plastering job itself.The skill of all the men working in the boatyard is on display by the finish, and water-tightness, of the completed hull. The skill of a good plasterer will result in not only arugged but a smooth and fair ship which will be viewed with pride by all who see anduse her.

Page ii VOLUME II CONTENTS

TABLE OF CONTENTS

Page

FOREWORD i

PLASTERER'S TOOLS AND THEIR USE 1

Hawk 1Standard Steel Trowel 5Swimming Pool Trowel 9Edger 10Sponge Float 11Darby 12

STAGE 3 - JOB 1

Task 1. Preparation for Plastering 16Mesh 16Plastering Crew 19Materials 19Equipment 20Scaffolding 21

Task 2. Plastering Day : 23Sand 28Cement 29Mixing Mortar 30Mortar Application 35

Step 1 — Application, Deck 35Step 2 — Application of Hull 39Step 3 — Plastering Inside the Hull 44Step 4 — Scrape Hull Outside Mortar Back to the Mesh 47Step 5 — Skin Coat 48Step 6 — Sponge Troweling, Deck and Hull 50Step 7 — Steel Troweling 52

Cleaning Up 56

Task 3. Preparations for Steam Curing 57Erecting the Steam Tent 57

Task 4. Steam, or Accelerated, Curing Temperature 59Temperature 59

Task 5. Second Phase Plastering 63Casting Keel, Engine Beds and Rudder Housings 63

Water Testing 67

Repair 68

Part 1 — New Construction Voids and Leaks 69Part 2 — Repairs in Service 73Two-Coat Plastering 73

CONTENTS VOLUME II Page iii

Multi-Stage Plastering 75

Cold Joints, Framework Method 75Cold Joints, Inverted Wooden Mold Method 77

Launching (photo) 79

-END OF VOLUME II -

INDEX OF TRAINING FILMS CORRESPONDING TO THIS TEXT

TRAINING FILM SERIES NO. 5862-1-72

Film No. Title

(10) Meshing Hulls-Preparation ForPlastering

(11) Plastering Tools and Mixing Mortar

(12) Plastering a 65' Hull

(14) Steam Curing

(15) Water Testing and Repairs

(16) Moving and Rolling Hulls

General Films

(17) Building a 65' Patrol Boat Hull

(18) Building a Fishing Fleet

Page iv VOLUME II

PLASTERING TOOLS

AND

THEIR USE

PLASTERER'S TOOLS AND THEIR USE VOLUME II Pagel

PLASTERER'S TOOLS AND THEIR USE

The basic hand tools required for applyingthe finishing mortar on cement hulls are:

A — Swimming pool trowel.B - Hawk.C - Standard 4" x 12" (101.6 mm x 304.8

mm) trowel for application andsmoothing.

D - Edger.E — Smooth sponge float.F — Coarse sponge float.G - Water brush.H - Bucket

A hawk has a serrated top to stop mortar fromsliding off.

The hawk has a comfortable sponge cushion tomake it more comfortable to hold.

THE HAWK AND HOW TO USE IT

A hawk consists of 12" square (304.8 mmsquare) aluminum plate with a wooden handleattached to the bottom center. The hawk isnormally held by the handle in the plasterer'sleft hand. It is used to hold the mortar whilethe plasterer is applying it to the hull. The fol-lowing sequence illustrates how to hold and usea hawk.

VOLUME II PLASTERER'S TOOLS AND THEIR USE

First, a quick stir to the wheelbarrow-load ofmortar.

Scooping the mortar right onto the hawk.

Use both the trowel and the hawk to loadthe hawk.

PLASTERER'S TOOLS AND THEIR USE VOLUME II Page 3

Don't load the hawk too full.

Trim the mortar off the edge of the hawk.

The mortar is scooped right off the hawk ontothe hull.

This shows the position of a plasterer's hands whileeffectively applying the mortar to the hull.

A helper loads a hawk with a shovel.

Hold the hawk under the work to catch the mortarwhich falls back.

Loading a hawk from a mortar board.



STANDARD STEEL TROWEL

The standard steel trowel has a 4" x 12"(101.6 mm x 304.8 mm) stainless steel face.A wooden handle is attached to the back. Thehandle is bolted onto a casting which is rivetedto the trowel blade. Care must be taken notto damage the sharp edge of the trowel. If theedge of the trowel is nicked, the nick will dragmarks over the work as the mortar is beingspread and smoothed. Care must also betaken to keep the trowel handle securelyfastened. If the handle is allowed to becomeloose the plasterer will not be able to controlthe trowel. The following sequence illustrateshow to use a trowel.

Standard trowel.

Balance the trowel in the hand.

Use the fingers in guiding the blade in overheadstrokes. Be sure to keep the back of the troweland the trowel handle clean. If mortar isallowed to build up on the back of the trowelthe sand in the mortar will soon blister thehand of the plasterer

Always keep the nut on the back end of thehandle tight thus preventing the handle fromturning.


The front end of the trowel handle is recessedto receive the bolt which ho/Ids the handle.If the handle is allowed to become loose thiswood recess may become damaged and it willnot be possible to keep the trowel handle tightafterwards.

The proper way to apply mortar. Punch themortar off the hawk against the hull. If themortar is punched it will penetrate all the waythrough the mesh. Never spread the mortaroff the hawk.

Only after mortar has been punched against thehull is it spread.


Mortar which has penetrated the mesh properly.

This illustrates a series of trowels of mortar whichwere punched on. After the whole area is goneover in this manner, the mortar will be spread.

This man is illustrating how NOT to apply mortar.

VOLUME PLASTERER'S TOOLS AND THEIR USE

He is applying a thin skin on the outside of the hullmesh and spreading it.

A thin skin of this type only penetrates the outerlayers of mesh. If mortar is applied in this wayfrom both inside and outside the hull a laminationwill result between the two layers. There will bemortar on the mesh on both sides of the hull shellbut air pockets will be formed against the rods.If this occurs these voids will eventually fill withwater and could seriously damage the steel reinforc-ing thus considerably shortening the life of thehull.

This is an area shown from the inside where theplasterer has merely spread the mortar rather thanpunched it against the hull. Mortar spreak like thiswill leave pockets of air in the reinforcing.


THE SWIMMING POOL TROWEL

The swimming pool trowel is much thesame as the standard plasterer's trowel exceptfor its rounded corners. These rounded cor-ners prevent the edge of the trowel digginginto the surface of the concrete as the plas-terer trowels the finish smooth. A boat hullconsists of a series of compound curves whichare difficult to finish with a standard plas-terer's trowel without leaving ridges behindthe trowel as it passes over the work.

Swimming pool trowel with stainless steelblade.

The swimming pool trowel is used for finishingwork. Here the hull has just been sponge-floatedand the plasterer is now starting the first part ofsteel troweling.

The swimming pool trowel is first used to applythe skin coat.


This illustrates the shape of the swimming pooltrowel.

THE EDGER

The edger is a small rectangular trowel usedmostly for work in difficult corners. A plasterercustomarily carries this tool in his hip pocket anduses it frequently for cleaning off the back ofhis trowel.

The edger.

An edger being used to clean out a scupperhole.


SPONGE FLOAT

The sponge float is made on a wood oraluminum base. It has a wooden handle attachedto the back and a sheet of approximately 1"(25.40 mm) thick sponge rubber is affixed tothe base. The sponge rubber is obtainablein varying densities. The coarser sponge-faceleaves a coarse finish. The finer face gives asmooth finish. The coarser-faced sponge floatis used during sponge trowel when the mortarhas taken its initial set. The fine-face is usedfor the finishing before steel troweling withthe swimming pool trowel. The sponge trowelis used in a circular motion; it smooths thesurface of the mortar by flattening out anyridges and by moving the surface mortar intothe hollows. The sponge trowel can only beused when the mortar has started to set andthere is no longer water on the surface.

Sponge float.

(A) Coarse-faced sponge float.

(B) Fine-faced sponge float.

Here a coarse sponge float is being used tofinish a deck.


Here the surface is still a little too wet for asponge finish. Notice how the mortar isbeing left in ridges. On a large hull like thisone, sponge floating has to be started fairlyearly as all of the hull mortar sets up atabout the same rate.

On a small hull with a small surface areasponge floating can be done throughout atjust the right stage of mortar set. In thisway the maximum smoothing effect maybe achieved all over the hull.

The darby is not an issue tool but someplasterers use them to assist in finalfairing. The darby is being used hereto check for lumps on the hull mortar.


GALVANIZED BUCKET

The 21/2 to 3 gallon (9.56259 liters to11.355 liters) heavy duty galvanized bucketis the best size to use during plastering of aferro-cement hull. The buckets must bestrongly built to withstand the abuse receivedon plastering day.

Buckets are often tossed around and getdented.

Wet mortar is heavy. A bucket of thiscapacity is the maximum the plasterer'shelpers should be obliged to carry over allthe obstructions which have to be negotiatedon plastering day. These buckets are continuallybeing lifted up to the deck from the floor.

Always have a drum of water close to themortar box so that the buckets can be rinsedafter each loading. This will prevent themortar from sticking to the bucket sides.If the buckets are not rinsed after each loadmortar will tend to build up making the bucketsheavy. This dead mortar may be inadvertentlydumped onto the hull along with a load offresh mortar, later causing problems.


WATER BRUSH

The water brush is a wooden-handled brushwith long, soft bristles. Its basic use is to flickgrout on the hull in final finishing. The plastereruses this brush to assist in cleaning his toolsthroughout the day.

Here a plasterer is flicking grout onto the hullto assist in lubricating the surface of the mortarduring final finishing. Note the edger in theplasterer's hip pocket.

Water Brush.

PREPARATION FOR PLASTERING VOLUME II Page 15

PREPARATION

FOR

PLASTERING

The yard gets ready for plastering.

The plasterers stand by.

The scaffolding is prepared.

VOLUME II STAGE 3-JOB 1

STAGE 3 - JOB 1PREPARATION FOR PLASTERING

The plastering of a ferro-cement hull is acritical point of construction. Mortar only staysplastic for a few short hours before setting hard.Careful planning and preparation must precedethe appointed plastering day. The following is acheck list of details which must be attended toprior to plastering a hull.

1. Mesh.

Is the mesh absolutely tight all over thehull? Special places to check are:

a. The decks: Check for tightnessall over. Be sure all the meshjoints are well secured.

b. The hatch coamings: Check thatthere are no loose ends of meshprotruding at the top. Ensure themesh is not rounded on the insidecorners of the coamings but is laidin tight to the corner vertical rods.There is no stress on hatch coam-ings so ensure the mesh joint atthe deck is square; do not let themesh radius here.

c. The bulwarks: Ensure the meshis laced back of the scupper holes.Check the mesh on the undersideof the bulwarks cap. The meshshould be laced very tightly here.Loose ends of mesh should be bentin against the screed. If stanchionsare used to support the bulwarksensure that the drainage holesagainst the bulwarks are in placeand that the mesh does not pro-trude around these holes. Themesh may form a straight radiusat the bulwark and deck joint butthis radius should be constant allaround the deck edge. The meshmust lie below the level of thescupper holes so that the mortarmay be matched with the bottomlevel of the scuppers to allow all thedeck water to run out freely.

Deck mesh ready for mortar. Hull meshed and faired, ready for mortar.Note how the scupper screeds project slightlybeyond the surface of the mesh. These screedswill finish flush with the concrete surface.

STAGE 3-JOB 1 VOLUME II Page 17

d. Hull: Check to ensure that themesh is tight and fair all over thehull. Be sure there are no loosehog rings or mesh ends protruding.Ensure the hull is absolutely fair.

e. Transom: If the transom isdesigned flat ensure that it re-mains flat. Watch for build-up ofmesh on the transom corners. Ifthe mesh builds up too heavilyon the corners of the transomvoids will occur at this point.Better too little than too muchmesh at the transom corner.

f. The Keel: Ensure that the meshis laced tightly at the bottom ofthe keel. Do not allow the meshto build up here. Two layers ofmesh are sufficient at the bottomof the keel. These two layers willallow any mortar scraped ordropped off the inside of the hullduring plastering to fall rightthrough the mesh. A second,double strip of mesh may beadded to the bottom of the keelafter plastering the hull prior toplastering the keel bottom.Remember the keel is constructedlike a concrete beam. The keelgets its strength from the heavyreinforcing rods used in this area.If the mortar which drops to thebottom of the keel during plaster-ing is not allowed to fall rightthrough it will remain there inthe form of loose sand with nostrength. This will always be aproblem area later for the keelbottom will become a primesource of leaks. When the ballastis poured into the keel the freshmortar cannot work itself aroundthese lumps of old mortar. A con-crete beam or keel only becomesstrong when the fresh mortarcompletely embeds the steel rods.

g. Bulkheads, webs and stringers:Ensure that there is no build-upof mesh on the corners of thebulkheads where they join thehull. If the mesh builds up onthese corners, there will nearlyalways be a hollow at the cornerafter plastering and this will bea second major source of leaks.Four layers of mesh are sufficientfor these areas. The mesh shouldbe trimmed at the corner; itshould not lap over onto the hullmesh. Ensure that all the limberholes are in place on bulkheads,webs and stringers.

Mesh is not lapped at webs and bulkheads.Note: The heavy reinforcing in the keel box andhow the mesh is left off the keel bottom to allowwaste mortar to drop th ough.

VOLUME II STAGE 3 - J O B 1

If the mesh is not laced in tightly it will bulgeout when the mortar is pushed through.

h. Stern tube: Again, do not allowthe mesh to build up here. Ensurethat the design permits the dead-wood cavity to be poured solid.This is normally a difficult area topour mortar into, for the sterntube is nearly always as large indiameter as the width of the dead-wood area inside. The deadwoodis also built like a concrete beam.The vertical hull reinforcing rodswill all be welded to the stern tube.The normal mesh lay-up should beterminated 6" (150 mm) above andbelow the stern tube in the solid

deadwood area. Use only 2 layersof mesh here so that the mortar maybe packed in tightly around thestern tube.

Only when all the above-mentioned areashave been prepared should a date be set forplastering. Too often the plastering crews areorganized for a specific date, the meshing is notcomplete, and the above-mentioned areas arerushed through and not attended to properly.If these areas are not meshed properly, a roughplastering job will result and the hull will befull of voids around the keel, shaftlog, bulkheads,webs and stringers. Even in a production yardit is better to leave a finished hull sit for a weekwhile plastering is organized rather than goinginto expensive overtime or not doing this lastjob properly. Remember that undoing mistakesand neglect after plastering is hard work andexpensive.

Example showing stern tube of equal diameterto width of deadwood.

Mesh clipped in around the bulwarks capscreed.


2. Plastering Crew.

To calculate how many men will be neededuse the following rule of thumb guide;

1 applicator—finisher and 2 laborersfor every 200 sq. ft. (18 m2) of hullsurface to be plastered.

When selecting commercial plasterers to dothe application and finishing be sure they under-stand that the mortar has to be punched againstthe mesh when applying it and not spread overthe mesh as in normal plastering work. If thevessel has over 1500 sq. ft. (140 m2) surfacearea employ a plastering supervisor who willspecifically keep an eye on the consistency ofthe mortar mix as well as assign the plasterers'duties and check each individual's work. Asecond man should be in charge of coordinatingthe helpers; he will work closely with theplastering foreman.

Ten hours is the maximum length of timemen will be able to work effectively on the job.There is a certain amount of energy required toplaster a hull properly so be sure there areenough men on hand to complete the job totallyin this time and clean up afterwards. If too fewmen have been employed, two areas will nor-mally reveal this deficiency. They are (1) theinside of the hull will be poorly finished, requir-ing much work later to make it presentable, and(2) the work site will be left in a mess. The areaunder the hull, mortar boxes, buckets, etc., willbe encrusted with hardened concrete, left thereby men who became too tired to pay properattention to cleaning up at the end of the plas-tering day.

Sufficient manpower must be employedbut they must be effectively deployed. Propersupervision of the men is as important as thewilling workers themselves.

A second rule of thumb may be used. Thisis that the work must be laid out so that all themortar is applied to the hull within the first3 hours of starting the job. If all the mortar is notapplied within this time, the men will become tootired to finish the job properly. An experiencedcrew will normally have the job finished andcleaned up within eight or nine hours afterstarting, allowing one hour for breaks.

The Foreman Plasterer assigns his men to theirrespective sections of the hull.

The bagged sand and cemen t stored on pallets.


3. Materials.

For specific information on sand andcement refer to Task 2, page 28.

As a guide, order one 94-lb. (42 Kg) bagof cement for every 15 sq. ft. (1.3 m2) of hullsurface area to be plastered. When consideringsurface area add the total ferro-cement surfacearea of the hull which includes deck, webs,bulkheads, coamings and floors. One 94-lb.(42 Kg) bag for every 15 sq. ft. (1.3 m2) ofsurface area allows a good margin for wastageand ensures that there is ample cement to com-plete the job. Extra quantities of cement willbe required for filling in the keel, enginebearers, etc., at a later date. Remember thatlabor is by far the most expensive factorduring plastering. If the job is delayed forlack of materials, the delay will be costly.

Cement is the key factor for calculatingthe material quantities required for it is thenormal practice to batch sand and additivesat a proportion of so much per bag of cement.It is unwise to design mortar barches calcu-lated on partial bags of cement. Order thenecessary sand and additives to combine withthe quantity of cement ordered.

4. Equipment.

If a vessel has under 1500 sq. ft. (140 m2)surface area, 1 mortar mixer will have sufficientcapacity to do the job. Two mixers will be re-quired for jobs over 1500 sq. ft. (140 m2). Donot attempt to plaster hulls of over 3000 sq. ft.(280 m2) in one day but go into a multi-stageplastering operation. (See page 75 on multi-stage plastering.)

In conjunction with every mortar mixeruse 3 rubber-tired construction wheelbarrows.Three 55-gallon (208 L) water drums will alsobe required beside every mixer.

For every 200 sq. ft. (18 m2) of hullsurface area 1 plasterer is needed.

A good rule of thumb calculation for eachplasterer's hand equipment is the following:

2 — 3-gal. galvanized buckets.1 - 2' x 2' x 1/2" (600 mm x 600 mm x

13 mm) plywood mortar board.1 — 3' (900 mm) high mortar stand.2 — standard steel trowels.1 — swimming pool trowel.1 — hawk.1 - edger.2 — sponge floats.1 — darby.1 — water brush.2 — pair gloves.

(Note: The extra trowels, floats and glovesmay be used by the helpers who may do the spongefloating inside the hull once the major work ofapplying the mortar is complete. See page 50.Three 4' x 8' (1250 mm x 2400 mm) mortar boxeswill be required for each mixer. Each mortar boxand wheelbarrow should be supplied with a long-handled, square-mouth shovel.

If steam curing is anticipated, steam distribu-tion pipes should be ready. A steam tent shouldbe prepared and material should be on hand formaking a structure to support the steam tent.Steam generators should be ordered. (See VolumeIII, Job 9.)

Two vibrators should be used if the hull is tobe built on the open cage method in the mannerof the 65' (19.5 m) power boat hull with a deckmold. Four vibrators will be required if the hullis to be built over a wooden mold.

STAGE 3 - J O B 1 VOLUME II Page 21

Sufficient water hoses will be needed toreach the nearest source of water. If 2 mixersare to be used have a separate hose and watersupply to each mixer.

All the above-mentioned equipmentshould be organized well in advance of plaster-ing day.

5. Scaffolding.

Scaffolding planks should be of a goodquality lumber which is nearly knot free.2" x 10" (50 mm x 250 mm) fir makes anideal scaffold plank. 14' (4.3 m) lengths arethe handiest to handle. If scaffolding is to beset up only one plank wide the plank should besupported every 6' (1.8 m). If two planks widescaffolding is used, these planks will safely span12' (13.6 mm) with 2 men working on it at once.

A 65' (19.5 m) hull will require a total of36 2" x 10" x 14' (50 mm x 250 mm x 4.3 m)fir scaffolding planks. These will probably havebeen ordered earlier in the job and will alreadybe on hand.

A kneeling pad to distribute the plasterer'sweight.

Scaffolding with steps and ladders. Short 2"x 4" 's (45 mm x 90 mm) timbers for the


Inside scaffolding will vary with each vessel.Each watertight section should have 2" x 10" x 7'(50 mm x 250 mm x 2.1 m) lengths of scaffoldingin it for the men to adjust as they require. Someshort lengths of 2" x 4" (45 mm x 90 mm) shouldbe put into the awkward fore and aft sections.

Each section of the hull should have two2' x 2' x 1/2" (600 mm x 600 mm x 13 mm)plywood pads for standing on. This will give aplasterer a means to distribute his weight shouldhe have to step on the hull in reaching an awk-ward corner. If these pads are not supplied aman will be obliged to step on the hull frame-work anyway to reach awkward corners andhe will bend the reinforcing rods in doing so,thus throwing the hull out of fair.

Keel blocks.

8 — 3' (900 mm) high saw-horses should beon the job. These will be used for gaining accessnear the stem and on the stern where it is awkwardto reach from a scaffold.

1 — a ladder should be placed in each water-tight section of the hull for access to the compart-ments.

1 — set of stairs should be erected at each endof the hull. These stairs should be strong enough toallow two people to pass on them while carryingmaterial on and off the boat.

Each set of stairs should have a landing stageat the top. The normal run and rise for stairs is7" (175 mm) high and 11" (275 mm) run. How-ever, in a work shop this may be changed to 8"(200 mm) high by 8" (200 mm) run. If a ramp isto be used it should be made three times as longas it is high, with cleats nailed across it for steps.

6. Hull Supports.

The last item to check before plastering arethe hull supports. If the hull is built upright usingoverhead supports the supports should run plumbto the overhead beam. If the beam is spanning morethan 12' (3.6 m), as they do on most hull supportstructures, additional diagonal supports should betaken to the corner of the support to prevent thebeam sagging.

Keel blocks should be prepared. Keel blocksshould be a minimum of 12" x 12" x 4' (300 mmx 300 mm x 1.2 m) long for the bottom blockand blocks of similar dimensions used up to thefinal wooden wedges driven under the hull. Keelblocks should be set up under structural bulk-heads and large floors.

Pipe supports under the stern.


If the stern overhangs the keel, pipe supportsshould be set up under this area to take theweight of the stern section. If a hull is designedto be a completed 20 tons dead weight, it willattain a weight of nearly 30 tons during plas-tering, taking into account the weight of thewater in the mix plus that of the men walkingaround on deck. The hull must be well bracedfrom as many points as possible so that nomovement will occur when the men start towork on it. The overhead structure must bewell braced to support this additional hullweight until the concrete sets hard enoughto bear its own weight.

LAYING OUT MEN

The mesh is now laced tight over the entirehull.

The materials and equipment required areall on hand.

The scaffolds are all erected and the hullis well braced.

The next stage is to plaster the hull.

The deck is plastered first The bucket brigademoves into action.

TASK 2 - Plastering Day

If plastering is scheduled to start at 8 a.m.have the plasterers and the helpers report for workat 7:30. This will allow the plasterers a few min-utes to browse over the job and familiarize them-selves with their day's work. By allowing an extra1/2 hour at the start of the job for the men torelax and examine the hull and the equipmentlay-out, they will all become familiar with thework and the supply system before the seemingconfusion of the mortar application begins.This also allows a little lead time to get themortar mixers fueled and checked, the waterdrums full, and the first batches of mortarmixed ready for the start. Further, electricalextensions for the vibrators and trouble-lightswill have to be prepared, and the buckets,shovels and wheelbarrows lined up.

At 7:45 call the plasterers into a groupand explain to them the basic difference betweenboat plastering and construction plastering. Howthey should concentrate on punching the mortaragainst the hull rather than spreading it as theywould in the regular plastering of a wall orceiling. Normal plaster lath is only one layerwhile the average ferro-cement lay-up is fromeight to twelve layers of mesh and two layersof rods.

Applying mortar under keel blocks, thenreplacing the blocks.


Loaded wheelbarrows are wheeled in.

The bucket brigade dumps the mortar directlyonto the deck; it is vibrated immediately.

A chain of buckets being filled and passed upto the deck.

STAGE 3 - J O B 1 VOLUME Page 25

Diagram showing where to assign the plasterers.

VOLUME STAGE 3 - J O B 1

Next, detail each plasterer to his appointedarea of the hull (see diagram on page 25). Thediagram shows how the 65' (19.5 mm) powerboat hull has been divided into approximatelyequal areas of 200 sq. ft. (18 m2) per man. Theplasterers working the deck have a slightly largerarea to cover, and the plasterers working thebulkheads and floors have a smaller area, becausethe inside of the hull is more difficult and time-consuming to plaster.

Starting at the bows the men work aft, to portand starboard

The wheelbarrows line up for fresh mortar.

Meanwhile, have the helpers standing to oneside in a group by themselves. First, detail off oneman for each vibrator. Next, detail off one manfor each wheelbarrow. Next, detail off as manymen as are required to start a bucket brigadeworking along the deck.

While the first helpers are being sent to theirvarious duties, several plasterers should remove thekeel blocks, plaster the areas under the keel formerlyin contact with the blocks, then replace them anddrive the wedges up tight against the keel.

The deck after one hour.

STAGE 3 -JOB 1 VOLUME II Page 27

The first large area to tackle is the deck.The deck will be plastered quickly. It shouldtake only one-half hour to apply all the mortarto this area. The vibrators will be runningconstantly while the deck is being plastered.It is difficult to plaster any other part of thehull while the vibrators are running for themortar will tend to fall off.

As soon as the deck is plastered the menon the bucket brigade will be free to assist theplasterers starting work on the hull. Detailthe helpers off one at a time. Stay with himuntil he demonstrates that he has understoodwhat he is to do and whom he is to workwith. Appoint an area off to one side wheremen who have finished a specific job can col-lect and be given a new job as the workprogresses. On a hull the size of the 65' (19.5 m)power boat, thirteen plasterers were requiredfor application and finishing. Two mixer menand one foreman plasterer were also employedmaking a total of sixteen men on the plasteringcrew. Thirty-two additional helpers wereused; that is to say, two helpers for every oneplasterer. With forty-eight men scrambling allover the hull, two mortar mixers roaring awayand three vibrators adding to the din, the jobwill quickly take on a semblance of absoluteconfusion. The job will quickly develop intoreal confusion unless the men are given goodleadership and constant guidance.

As soon as the plasterers have finishedspreading the mortar on the deck horizontalsurfaces they should start plastering the bul-warks and the bulwarks' cap which is a difficultand time-consuming area. Meanwhile the restof the plasterers are working to get all themortar applied to the hull before the hour of10a.m.

Next, the plasterers move to inside the hullto work on the appointed areas. While they areworking these interior sections, some of thehelpers will be scraping off the mortar on thedeck and the hull right back to the mesh. Whenthe concrete starts to harden, some of the mencan go inside the hull with sponge trowels andfinish off this area. The helpers working insideshould keep a sharp eye on the keel area towatch for loose scraped-off mortar and spillage.This loose mortar should be cleaned up regularlyand dumped.

Meanwhile, as the demand for mortardecreases, some men and their wheelbarrowsshould be detailed to shoveling up the scraped-offmortar and heaping it into individual piles whichare easily picked up once they begin to harden.

Send men off for breaks and for lunchonly in small groups so that work on the hullwill carry on without interruption. Pay particularattention to keeping the work site and the equip-ment constantly cleaned as the job progresses.If it is warm weather keep plenty of water cool-ing the floor beneath the hull so as to avoidhaving the hull mortar harden too fast. But,most important of all, the man in charge shouldbe continually inspecting the hull and the workarea, trying to anticipate problems before theyarise. The man in charge should be constantlyavailable to make quick decisions. It is a hecticday but there is only one day for plastering thehull.

i

Page 28 VOLUME II STAGE 3 -JOB 1

The following points should be borne inmind when selecting sand for use in ferro-cementconstruction:

1. Never use coral sand or salt-waterbeach sand.

2. Never use sand crushed from limestoneshell.

3. River sand is generally the best typefor ferro-cement. Generally it willhave been deposited over many centu-ries, created originally from igneousrocks, quartz, basalt, granite, etc.,and borne down by the river current.

4. Pre-bagged commercial sand is themost convenient to use, if availableeconomically, for these reasons:

a. The sand normally comes fromnatural deposits which are largeenough and of sufficiently highquality to justify commericalexploitation.

b. It is washed, graded, weighed andbagged.

c. Therefore, more easily stored andhandled than bulk sand.

d. Therefore, easy to batch withcement. For instance, three 100-pound (45 Kg) bags of sand andtwo 80-pound (36 Kg) bags ofcement make a good, one-batchmix in a standard size paddle-mixer.

e. Bagged sand is dry. Consequently,the water-cement ratio may bemore easily controlled than byusing bulk river sand which islikely to contain a varying amountof moisture.

f. Commercial sand-packaging plantscan supply accurate informationon their gradings of sand. It maybe necessary to mix 1, 2, or 3grades of bagged sand together toarrive at the required sand gradingmixture.

WHAT TO LOOK FOR WHEN SELECTINGSAND

1. Grading Size of Sand Particles

The accompanying chart shows what is con-sidered a desirable variation of particle sizes insand. The predominant particle sizes are for thosesands which will pass through a No. 8 sieve andyet be retained by a No. 50 sieve. The designa-tions "No. 8" and "No. 50" refer to the aperturesizes in the wire screens of the sieves; No. 8 being1/8 of an inch (3.2 mm) and No. 50 one-fiftiethof an inch. If a grain of sand is more than 1/50thof an inch in any one direction it will not passthe sieve. Long thin slivers of sand are an excep-tion and this is the second factor to avoid.

2. Sand Shape

The ideal shape is the diamond, flat-sided,bulky, yet tapering. Long, slivery sand should beavoided. Sand is the strength agent of mortar.Cement is the part which binds the sand particlestogether. A diamond shape will not shatter aseasily as a long, thin section. Diamond shapesnaturally interlock and compact more easily thando other forms of sand particles. Varying shapesand sizes will interlock around a predominantmass of diamond-shaped particles if each particleis completely surrounded by cement paste, ahigh-strength concrete will result.

3. Cleanliness

What is meant by clean sand is a sand which isfree from earth, humus, grass roots, clay, silt, orany particles which are not minute stones. If thereis silt present in the sand it will mix with the cementpaste and weaken it. Silt has no bonding power.

BULK SAND

In many areas it is uneconomical to obtaincommercially bagged sand. If bulk sand is usedit should be:

1. Stored within a retaining wall. Thiswill stop the pile of sand spreading outand getting mixed with foreign matter.

2. Bulk sand should always be screened toremove the coarser particles. It shouldbe shoveled through a No. 8 sand screen.


3. Screened sand should be keptseparated from the unscreenedsand.

4. A cover should be kept over thesand pile to keep out airborneforeign matter.

5. Avoid sand from crushed rock.It may be used if there is no othertype of sand available.

6. Avoid sand which has been dredgedout of tidal river beds or harborbasins. This is generally used for fillon construction sites but will notserve for cement.

SUMMARY

Sand should be clean and well graded. Onehundred percent should pass a No. 8 sieve, 30percent a No. 50 sieve, 5 percent a No. 100sieve. Larger particles of sand tend to make themix bind and wilt hang up on the mesh, therebycausing pockets behind each large sand particle.Coarse particles of sand also drag to the surfacewhen finished and scratch the hull surface. Toofine a sand requires too much cement paste tobind it together. This tends to make a weakerconcrete as the exact grading and particleshape forms the strength member and thecement is the glue or paste which holds ittogether.

Suitable sand will generally be found inmost countries with mountain ranges or oldhigh hills, or in those with rivers which flowfrom high hills and mountains.

CEMENT

There are four common types of Portlandcement available:

Type 1 — Standard cement, most com-monly used in construction.

Type 2 — Sulphate resistant and slightlyretarded, this cement takeslonger to set.

Type 3 — High, early-manufactured typeso that it will gain a high strengthquickly.

Type 5 — Sulphate resistant. When thiscement is manufactured a specialrock is chosen which will makethe resulting concrete resistant tosulphates.

All four types of Portland Cement have beensuccessfully used in ferro-cement construction.Choose the type of cement which is most readilyavailable locally. Choose only freshly-kilnedcement and avoid using cement which has beenstored for long periods.

THE COMPOSITION OF CEMENT

Portland Cement is a predetermined and care-fully proportioned chemical combination of cal-cium, silicon, iron and aluminum. Crushed rocksof these elements are burned in a kiln resultingin a cement powder so fine that a sieve capableof holding water will allow the cement to pass.The powder is so fine that one pound (1/2 Kg)of cement powder will contain approximately150 billion grains.

HOW TO STORE CEMENT

Cement will retain its quality indefinitelyif it does not come into contact with moisture.If it is allowed to absorb moisture it will setmore slowly and its strength will be appreciablyreduced. In storing sacked cement, the ware-house or shed should be as airtight as possible.

MIXING MORTAR

The ratio of water to cement will vary con-siderably according to each particular job. Thereare many factors which determine how muchwater should go into the mix. Some of thesefactors are:

1. The water content of the sand.

2. How much old mix remains in themixer from the previous mix.


3. The sand-cement ratio designated.

4. How the mix is to be applied: A mixwhich is to be used over a wooden moldand vibrated should be a little wetterthan a mix which is to be troweledover a mesh and reinforcing lay-upwith no mold to back it. (See photo.)

5. Ambient temperature.

Consequently, there can be no exact quan-tity of water given which will prove correct forall mixes for all applications. A trial batchshould be mixed at the start of operations soan approximation of water quantity per mixerload can be made and followed for the restof the day.

HOW TO OPERATE THE MORTAR MIXER(GASOLINE-POWERED):

1. First, inspect the mixer drum andpaddle blades. Ensure that there isno dried mix left on them from pre-vious use. Check that the mixerblades have not been worn too badly.

2. Once the mixer is clean, start theengine and let.it run for a couple ofminutes until it warms up.

Place approximately 80% of the esti-mated amount of mixing water requiredin the mixer.

Next, dump in the cement. Let thecement mix with the water for at leastone minute. Ensure that there are nolumps in the cement.

Last, dump the sand into the mixer.The mix will appear very stiff at first.Be careful not to make it too dry or themixer motor will stall. Slowly add waterto the mix until the desired consistencyis reached. Let the batch mix for twominutes.

Keep the mixer revolving and dump themortar carefully into the wheelbarrow.

Do not let the mix revolve too long inthe mixer. Do not leave any mix in themachine longer than 15 minutes afterfirst mixing. Once the water has comeinto contact with the cement the hydrol-ysis process will begin. As the hydrolysisprocess goes on, the mix will stiffen. Thepaddle wheel will keep the mix liquid,thus making it lose some of its strength.Further, there is a certain amount oftime required to transport the mix fromthe mixer and dump it into a distributionbox and from the box to its applicationto the hull. Any mortar over one-halfhour old should not be applied to thehull but dumped. Mortar is not expen-sive. Weak concrete is.

After every third mix the mixer shouldbe well washed out and cleaned priorto starting to mix a new batch ofmortar. A water hose with a strongjet will be sufficient to clean the mixerat every trial batch.

The mixers mounted on blocks prior to startingmixing. By having the mixer mounted on blocksa wheelbarrow can be filled directly from themixer.


Sand analysis graph.

Next, the cement.

After the water and cement are in, add thesand.

VOLUME II STAGE 3 -JOB 1

Dumping the mortar into a wheelbarrow.

wash out the mixer after every third batch.

Mix consistency where no mold is to be used.

A wetter mix to be used over a mold.


DISTRIBUTING MORTAR

1) Set up mortar boxes at strategic pointsaround the hull.

2) The wheelbarrows should follow an orderlyprocedure for filling. Have the traffic flowin one direction only around the hull.

3) A contractor's wheelbarrow full of mix isheavy. Be sure that there are no holes orbumps in the path which may cause a

4) The foreman plasterer shows a helper howmuch mortar to put on the plasterer'smortar stand.


7) Here a helper stands by with some mortar. Thehelper's main job is to have mortar always readyfor the plasterers without obliging the plasterersto move too far to get it.

5) Once the plasterers are working above groundlevel, they place their mortar boards right onthe scaffolds beside them.

The mortar buckets are only partly filled. Thereturning buckets are dipped into a tub ofwater and rinsed prior to refilling with freshmortar.

Mortar is carried up to the deck in buckets andpassed down to the men working in the hull.


MORTAR APPLICATION

To do a good job of applying and finishingthe mortar on a ferro-cement hull there areseven distinct stages of application and finishing.If one step is not done properly and in propersequence a poorly finished vessel may result.Again, using the 65' (19.5 m) power boat hullas an example, the plastering steps are asfollows:

Step 1 — Application; deck.

Step 2 - Application; outside hull.

Step 3 — Application; inside hull andbulkheads.

Step 4 - Scrape back to mesh hull anddecks.

Step 5 — Skin coat.

Step 6 — Sponge trowel hull.

Step 7 - Steel float hull.

STEP 1 - APPLICATION OF DECK MORTAR

Application Time — 1 hour.

3 — plasterers-applicators required

2 — vibrator operators.

Sufficient labor to transport the mortarquickly from the mortar mixer to the area ofdeck being plastered.

1) Start at the stem. Dump the mortar outof the buckets into piles on the deck. Insertthe vibrator head into the mortar piles andvibrate until the mortar disperses into the mesh.Do not attempt to spread the mortar over alarge area with the vibrator. Instead, shift theexcess mortar with a trowel.

2) Work aft along the deck. The plasterersfollowing the men dumping the mortar ontothe mesh and vibrating it. The plasterers applymortar to the hatch coamings as they workback along the deck. They spread the mortaras they go, scraping up excess mortar and put-ting it into the piles being vibrated.

3) The men operating the vibrators pay particu-lar attention to the joint between the deck andthe hull. Allow the vibrator to rest a few momentsat all spots along the deck edge. Vibrate thispoint until the V-gap is completely filled. Whenvibrating ensure that there is plenty of mortarstacked up on deck above the vibrator. If thelayer of mortar above the mesh does not at leastequal the thickness of the mesh to be filled voidswill occur. While vibrating the deck edge haveone man check the outside of the hull. It is easyto see when mortar has completely filled thisjoint as it will emerge in an even, thick bandthrough the hull mesh along the deck sheer line.

Start applying mortar to the deck at the stem.


Working along the central gang-plank the bucketbrigade rapidly brings up mortar.

5} Continue working back along the deck untilall the mortar is applied. Spread any of the excessmortar scraped up.

6) After all the mortar is applied to the deck,the plasterers assigned to the deck concentrateon applying the mortar to the bulwarks and theunderside of the bulwarks cap. This is an awkwardarea to get at with a trowel. Mortar will have to beforced up under the bulwarks cap in the best waypossible. The mortar will be punched through thebulwarks from the decks. The men workingupwards on the outside of the hull will finish theoutside of the bulwarks off. Once the bulwarksare finished from the inside the hatch coamingswill be attended to.

Be sure there is excess mortar over the area beingvibrated so the mortar will flow into all airpockets.

4) Do not plaster the bulwarks at this time.The bulwarks and bulwarks cap take a lot of care-ful attention. There is not time while the deckis being vibrated to do these areas. It is vitalthat the mortar is applied to the deck as quicklyas possible so that the other plasterers maystart work on the hull. Work on the hull cannotbe carried out satisfactorily while vibrators arebeing used anywhere on the structure as themortar applied to the horizontal planes willtend to fall off the mesh. Dump the mortar directly on deck.


Check the edge of the deck to ensure that themortar is penetrating this "V" joint properly.

Foredeck once initial mortar has been appliedand prior to scraping excess mortar back tothe mesh.

The plasterers apply mortar to the hatch coamingsas they work along the deck; they do not plasterthe bulwarks at this time.

The deck mortar, well vibrated, being forced throughthe hull exterior mesh after filling the "V"-groovebetween deck and hull.


The plasterers scoop up excess mortar and pushit back to the areas being vibrated.

Mortar is dumped directly into holding boxesfor redistribution.

The helpers hold their feet on the vibrator headsto stop the heads from prancing around the deckand splattering mortar over the men nearby.

As soon as the deck mortar is applied the mentransfer to the hull exterior.


STEP 2 - APPLICATION OF HULL MORTAR

Application Time — 2 hours.

1 - plasterer per 200 sq. ft. (18 m2) ofsurface area.

Helpers as required.

1) The keel area in contact with the keelblocks should be plastered prior to plasteringthe deck. The weight of mortar placed on thedeck will have caused the hull to settle on thekeel blocks making them difficult to removeif these areas over the keel blocks have notbeen plastered prior to plastering the deck.Once the keel block areas are plastered thekeel blocks should be replaced and wedgedfirmly in place.

2) After the deck is plastered the plasterersassigned to the hull start applying the mortarto their appointed areas. Work starts at thebottom of the hull at the keel sides and themen work up the hull to the bulwarks cap.The men apply the mortar by scooping themortar off the hawk and punching it hardagainst the hull mesh. The entire hull isworked over in this way. As the mortar ispunched through a small area the plastererspreads the excess mortar over the surfacepushing hard. The mortar is applied fromthe outside of the vessel, and from the bottomto the top, for the following reasons:

a) A lot of work is saved by applyingthe mortar from the outside. Ifthe mortar was applied from theinside of the hull it would all haveto be lifted up to the deck andpassed down to each hull sectionbeing plastered.

b) It is more awkward to work insidethe hull than outside. By applyingthe mortar from the outside largeareas are covered more quickly.

Application of the hull mortar starts at the keelside.

The horizontal surfaces of the hull require hardpunching to get the mortar to penetrate themesh properly.

After the mortar is punched into the mesh it is spread.


Helpers keep the plasterers supplied continuallywith mortar.

3) When large amounts of mortar are handeddown into the hull there is a certain amount ofspillage. This spillage generally gets trampledinto the mesh and sets quite rapidly through beingsmall quantities by themselves. It is difficult towork mortar past an area which has had mortarspilled on it previously and has already started toset. Any mortar which spills from the outsideof the hull merely falls to the floor or is caughtby the plasterer on his hawk to be pushed backonto the mesh immediately.

4) Some of the horizontal surfaces of the hullare difficult to plaster from the outside, especiallyunder the stern of the vessel and up under thebilges. However, these difficult areas are generallynot so large and the plasterers should resist thetemptation to plaster them from the inside forthe following reasons:

a) Excess water in the mortar is carriedby gravity downwards. This excessmoisture will collect on the bottomsurface of the horizontal mortar layer.This wet surface makes mortar pressedagainst it difficult to adhere. Mortarapplied overhead has to rely on frictionto keep it in place until it sets. If thereis moisture on the mesh, the mortarwill not hang in place.

b) Once the mortar applied on the hori-zontal surfaces from the outside ofthe hull takes its initial set, mortar canbe forced against it from the insidewith no danger of the outside layerfalling off. Working from the insideof the hull the plasterers can work itdown hard and force the mortaragainst the outside layer more easilythan doing it in reverse. Adequatepenetration of the mortar into themesh will be ensured.

A plasterer checking over his work and applyingmore mortar to an area where penetration wasnot perfect.


Good scaffolding makes work easy.

c) If there are insufficient staples on theouter layer of mesh in any squarefoot area of the hull, the weight ofthe mortar applied to the mesh willcause the mesh to sag away slightlyfrom the hull framework. If themortar has already been appliedfrom the inside a layering effect willresult. A void will be left in thecenter of the thin concrete shellwhere the two layers of mortar haveseparated. Water will find its wayinto a void of this type, which can-not possibly be advantageous, espe-cially when the total thickness ofthe finished hull is less than oneinch (25 mm).

The inside of the bulwark being finished.

This mortar will be scraped back to the scupperscreed.

A plasterer punching the mortar against the hull.


5) The keel bottom is not plastered at thistime for two distinct reasons:

a) Again, the water in the mortar runsby gravity down to the keel. The areaaround the bottom of the keel remainsmoist for several hours after the restof the hull mortar has set. It is diffi-cult to get mortar to hang onto theunder surface of the keel bottomuntil the excess moisture from thehull has disappeared.

b.) During Step 3, while plastering insidethe hull, a certain amount of mortarinevitably falls into the keel cavity.This waste mortar must find a wayout through the bottom of the keel orserious consequences will result. Onall hulls inspected in service whichwere plastered with no way of dispers-ing the mortar which falls into thekeel cavity, the keel concrete wasfound to have little strength and wasoften riddled with voids for the firstseveral inches up from the bottom.A large majority of hulls plasteredthis way experience weeping upthrough the keel bottom due to thissection being filled with lumps ofloose mortar. The only remedy forthis weeping once it has occurred isto pour bucket of watery grout intothe keel and vibrate it thoroughlyonce the hull is cured and prior toballasting. Keep pouring groutuntil it is to the level of the topof the waste mortar in the keel.This grout will seal any cracks inthe bottom of the keel. Do not usemore than is necessary to ensure thatthe bottom of the keel becomes solid.There is a lot of shrinkage in thegrout itself and little strength exceptas a form of glue to bind the lumpsof mortar already in place solidlytogether.

6) Continue applying mortar in an upwardsdirection on the hull to the bulwarks cap, work-ing the mortar in hard to obtain maximumpenetration of the mesh.

The hull during application looks a mess.

7) As the plasterers work up the hull sides, someof the helpers should go inside to inspect howmuch mortar is being forced through the mesh.A good applicator will push the mortar rightthrough the inner side of the hull mesh. Anaverage applicator will leave some of the insidelayers of rods exposed with the outside rodscovered, while a poor plasterer will leave someof the outside rods still visible from inside thehull. A poor plasterer is one who spreads themortar like house stucco. Where an applicatorhas accidently not achieved good penetration,the helper should poke a 6" (150 mm) longU-shaped tie wire through the hull as an indicatorto the plasterer for him to go over that areaagain. The plasterer will poke the wire backwhen he has re-done the particular area. Thehelpers should not be more than 5 minutesapplication time behind the plasterer in advisingpoor penetration for the mortar will start to setand no more mortar can be pushed against thatarea.


This photo graphically illustrates what happenswhen a plasterer adds water to old mortar andapplies it to a hull. It is a great temptation toa plasterer to scoop up a lump of semi-hardmortar which is laying on the floor or in awheelbarrow, rejuvenate it with water andpatch up a small area during final finishing.It will be easier to do this than restart themixer but the results will be disastrous.

Mortar punched onto the hull mesh from theoutside merges with the well-vibrated deckmortar. (Inside, barely discernible throughthe mesh, is a helper checking for penetration.)

All the good welding and mesh work is beingfinally buried in mortar.


STEP 3 - PLASTERING INSIDE THE HULL

After the plasterers have applied the mortarto the outside of the hull they should immedi-ately go inside and spread mortar over theexposed mesh. While inside they should alsoapply mortar to webs, bulkheads and knees.

1) Inside plastering should start at the deckand work downwards. The plasterer shouldload the mesh with plenty of mortar and workover a selected area, working from it in severaldirections. While troweling he should pressthe mortar firmly into the mesh, endeavoringto get maximum penetration of the mortarinto the mesh and filling all voids.

2) Knees

First apply the mortar to the hull aroundthe knees ensuring that the hull outer mortarbehind the knees is solid before plastering theknees themselves. Force the mortar into theknees and bring it level and even with theT-bar screed. Do not make the knees thickwhere they join the hull. Maintain them at amaximum 1" (25mm) thickness throughout.

3) Stringers

Do not plaster the stringers until the insideof the hull has been skimmed to the stringers.Plaster the stringers in the same way as the knees.

The hull is skimmed prior to applying the mortarto the bulkheads.

Pay particular attention to the corners of thestringers where they join the bulkheads. Workthe mortar well into this joint. Do not coverthe drain holes left in the stringers which allowwater to run into the bilge.

4} Webs and Sole Supports

Plaster the webs and sole supports next.While skimming the inside of the hull, work themortar well into the base of the webs where theyjoin the hull. Again, keep the thickness down to1"(25mm).

The mortar is applied at the top of the bulkheadsand the plasterers work downwards.

STAGE 3- JOB 1 VOLUME II Page 45

5) Bulkheads

Plaster the bulkheads last. They are plas-tered in the same manner as the hull. Be carefulto straighten out any bulges in the bulkheadsonce all the mortar is on. A bulkhead spreading13 ft. (4 m) and 8' (2.4 m) high will easily developa bulge of 2" (50 mm) or more in its center area,outwards from the side which was plastered last.Concrete bulkheads are very stiff bulkheads oncethe mortar has set but they are quite flexibleuntil this time.

6) Once all the plaster is applied on the insideof the hull the balance of the work here will beleft to the helpers who will now be finished sup-plying fresh mortar. Allow 1 hour for the mortarto set then have the helpers take scrapers insidethe hull and scrape the mortar back to the meshover the entire inner surface. A good plasteringjob should show a mesh pattern all over theinside of the hull. Once the excess mortar hasbeen scraped off the interior mesh of the hullsend in buckets to clean out all the old mortarspilled into the keel cavity, or have the helperspoke it through the keel mesh with rods.

7) Next, the helpers sponge trowel the entireinside of the hull. There are a lot of corners tosmooth out and a lot of area to cover. The 65-ft.(19.5 m) power boat requires 16 helpers withsponge trowels for 2 hours to dress up theinside properly.

8) Engine Beds and Rudder StuffingBox Supports

Plaster a thin skin coat over the outsideof these structures. Do not apply the mortarhard here but merely spread it thinly overthe mesh to create a form to contain the mortarwhich will be poured and vibrated into thesestructures once the hull has been cured.

A sample of average penetration.

Using the hawk inside the hull.

Applying mortar to a stringer.

.

Page 46 VOLUME II STAGE 3-JOB 1

Mortar penetrating to the inside of a hatchcoaming.

Men working inside the hull (seen through abulkhead).

Skin coating the engine beds.


STEP 4 - SCRAPE THE HULL OUTSIDEMORTAR BACK TO THE MESH

While the plasterers are working inside thehull a crew of helpers should be detailed off toscrape the excess mortar off first, the decks,then the hull. Simple steel scrapers may bemade up or 1' x 6" x 1/2" (300 mm x 150 mmx 13 mm) plywood boards will serve. Scrapethe mortar back until the surface mesh is ex-posed over the entire outside surface of thehull. The mortar is scraped back for tworeasons:

1) Weight. It is difficult to gauge thethickness of the mortar over themesh if surface mortar is not scrapedback after application. Extra weightdoes not mean extra strength. Theprinciple of ferro-cement is to leaveas thin as possible a layer of mortarcovering the mesh. By scraping themortar right back a skin coat of newmortar may be applied to a con-trolled thickness.

2) Key. A doubtful bond may occurbetween mortar which has nearly setand fresh mortar applied several hourslater. Cured concrete seems to bondbetter to new mortar than does semi-hard mortar to new mortar. The ex-posed wire mesh gives an additionalkey between the layers of fresh andolder mortar, as does the rough sur-face left by the scrapers.

A helper uses a board to scrape excess mortar offthe hull mesh inside and outside.

The mortar is scraped back to the surface mesh.This will enable the plasterers to control thethickness of the skin coat which is applied last.

A man scraping mortar off near the bow.


1) Mortar may have to be built up forsuch critical points as the bulwark sheerline or rail cap. The edge of the transommust also be built up so that a constantradius may be molded onto it.

2) Hatch coamings should be squared offneatly at all corners.

3) Scuppers should be faired into the deckand bulwarks.

The mesh is left exposed.

STEP 5-SKIN COAT

When the mortar on the outside of the deckand the hull has taken its initial set a thin skincoat of fresh mortar should be spread over thesurface. This skin coat should be troweled onsmoothly about 1/8 of an inch (3 mm) thick.Mortar of the same mix and water content as wasused previously on the hull should be used forthe skin coat. As the hydration process isadvancing rapidly in the first applied mortar atthis stage the skin coat will only take about onehour after application before it can be worked.The skin coat is applied with the same plasteringtechnique as is used to spread plaster over a wall.

The mesh pattern' makes a good key for theskin coat.

Applying the thin skin coat at the bow.


Building up mortar on the bulwark cap edge.

The darby is used to fair this critical area.

Mortar is stacked on the bulwarks cap andworked around the sheer-line.


STEP 6 - SPONGE TROWELING DECK ANDHULL

The deck is given a sponge trowel finish.This finish is carried up the inside of the bulwarksand under the cap. The hatch coamings are alsosponge troweled inside and outside.

1) Sponge troweling should not be starteduntil the mortar has taken its initial set.The sponge trowel is worked in a circu-lar motion, the idea being to smoothout the ridges and shift the top layerof mortar into any hollows. As themortar begins to set hard sponge trowel-ing becomes more difficult. Resist thetemptation to keep dipping the spongetrowel into a bucket of water in orderto shift the surface mortar more easily.Rather, have all available men take upsponge trowels while the surface isstill easily workable.

The mortar is faired into the hull.

The built-up mortar is allowed to set prior tofinishing.

Skin coating the deck.


Overall view of deck being finished.

Sponge troweling the deck. Fairing up a scupper.


2) The hull is sponge troweled in thesame way as the deck. However,a good finisher with a steel swimmingpool trowel should work right behindthe man who is working the spongefloat. He will trowel the hull to aglossy smooth finish immediately afterthe pass with the sponge float.

STEP 7 - STEEL TROWELING

The hull is gone over at least twice, firstwith the sponge floats, then with the steel trowels.If the hull mortar can still be worked have themen go over it for a third time. The more trowel-ing and finishing the better the resulting hullfinish. If the mortar has set too hard before thetroweling pass is completed the plasterer may flicka little water cement grout over the surface tobe worked. This grout will help lubricate histrowel. The grout should be used sparingly forit will turn to powder once the hull cures andhas to be cleaned off before paint will adhere tothe hull surface.

Finally, when the hull and decks are finished,the inside is neat and all spilled mortar clearedup, skin coat the bottom of the keel.

Sponge troweling.

Sponge trowel being used in a circular motion. Starting steel trowel floating over sponge troweling.


Steel float presses the surface sand back intothe hull mortar.

Result of the first pass of the steel trowel onthe hull.


Packing the mortar under the bulwarks cap withthe edging tool. An awkward area to work.

Sponge finishing the inside and the outside of thehatch coamings to conform to the T-bar screed.

Decks, coamings and bulwarks sponge finishedand looking trim.


Putting a steel trowel finish to thestem-head.

A final touch to the steel trowel finish atthe stem-head edge with a piece of plasticsheeting.

The morning after plastering day; wetting the hullsurfaces down as the steam tent framework isbeing erected.


On a hot day spray water under the hull to stopflash setting.

At the end of the day clean all mortar boxes, etc.

CLEANING UP

Plastering a ferro-cement hull represents along, hard day's work. The tired men will natur-ally want to go home as soon as their work is fin-ished. Their work cannot be considered finisheduntil the cement on every article of equipmentused during the day has been thoroughly cleanedoff. As well as cleaning off the equipment, thewhole area must be hosed down and cleaned.

1) Washing Hand Tools

Collect all the hand tools used duringthe day. Place them conveniently closeto a hose with a group of men detailedto ensure that all the dried concrete isthoroughly cleaned off. Supply severalstiff brushes and scrapers to assist intheir work.

2) Washing Equipment

Rinse the mixer out and clean it thor-oughly. Again, use a stiff brush and ascraper to get any hardened mortar offthe paddle blades and out of the drumcorners. Hose and brush off the out-side of the mixer. Attend to the mortarboxes, mortar stands, etc. Clean themoff and leave them ready for anotherday's work.

3} Clean up the general work areas aroundthe mixer, under the hull, and aroundthe mortar boxes. Be careful that theman washing down the floor does notspray water on the fresh plastered hull.Have one man work with the man onthe hose. He should use a long-handledscraper to remove dried lumps of mortaroff the floor. Leave a good-sized poolof water lying under the hull. Theevaporation of this water will raise thehumidity around the hull and preventit from drying out prior to steamcuring.

4) Finally, wash off all the scaffoldingplanks. Pick up all the empty sandand cement bags and generally makethe whole area tidy.

Clean up all the tools.


Light framework for steam tent.

Nail battens on plastic joints.

Steam tent erected.

ERECTING THE STEAM TENT

The steam tent should be large enough toclear the hull surface. No part of the tentshould come in contact with the hull oncesteaming commences. The tent should alsobe as air-tight as possible. At the same timethe tent should only be large enough to justcontain the hull. Each additional cubic footof the steam tent has to be heated to therequired temperature, thus demanding extrasteam heat from the generator.

Plastic sheeting, 4 mil thick, makes anadequate cover for a steam tent in those caseswhere only a few boats are to be produced.


If many hulls are to be made, a more permanentsteam tent made from rubberized canvas shouldbe purchased.

There is little weight to the steam tent so alight 2" x 4" (45 mm x 90 mm) wooden frame(see photo) will be sufficient. Be sure to usesome diagonal braces on the structure to preventit collapsing. A heavier structure will be requiredif the hull is to be steamed out of doors.Furthermore, if the hull is to be steamed outof doors in cool weather a double layer ofplastic sheeting should be used. One layerfastened under the wooden support structureand one layer over the support structure. Thiswill form a closed air pocket between the layersof plastic sheeting and assist in maintaining thetemperature in the tent. Battens should benailed over all the sheeting joints if steamingout of doors for the wind may come up andrip the steam tent open during steaming.

Start erecting the steam tent first thingin the morning after plastering. A hull shouldbe allowed a minimum of 12 hours afterfinishing before steam curing begins. Thehull may be steam, or accelerated, cured forup to 4 days after plastering provided thehull has been kept damp during this period.

Finally, before commencing curing, knocka couple of drain holes in the bottom of thehull to let any condensed steam water trappedinside run out. Avoid shock loading thehull at any time prior to steam curing. Do nothammer wedges under the bilge. Do not cut mainsuspension braces; intermediate braces may becut with caution. Do not jump down intothe hull or jump onto the decks, at this time.Treat the hull as being fragile until aftercuring.

Keep plastic clear of the hull.


TASK 4 — Steam, or Accelerated, Curing

Steam curing is preferred to the 28-daycold water wet curing for the followingreasons:

1) Steam curing is completed in 24hours. Other work on the hullmay then start.

2) Hulls which have been steam cureddo not normally have shrinkagecracks to the extent of most hullswhich are 28-day wet cured,

3) There is far less mess with steamcuring than with wet curing.

4) A better control of the cure can bemaintained with steam curing. It isdifficult during wet curing to keepthe entire hull wet. Dry spots willnormally develop where a sprinklerdoes not quite reach. Strict watchesshould be maintained for 24 hours,during steam curing while a similarwatch system would be very expen-sive to maintain for 28 days.

5) If a hull is built in a wooden buildinga 28-day wet cure could probablyruin the building. Floor joints willstart to rot from the prolonged damp-ness, materials stored in the buildingwill become soggy and possiblydamaged. All in all, the 28-day wetcuring method has many drawbacks.

TEMPERATURE

Raise the temperature slowly and try tomaintain it between 140 and 160 degrees fahren-heit (60 to 72 degrees centigrade). Avoid goingover 160° F (72°C). The enclosed steam curingchart, as used on the 65' (19.5 m) boat hull, is agood example of the steaming temperature curveto try to strive for. The term, "to try and strivefor," is used because steam generators have beenfound to be temperamental. They may some-times break down 3 or 4 times during the 24-houroperation due to one reason or another. That iswhy two generators should always be madeready. Two generators will ensure gettingthe temperature up to the proper level and, ifone breaks down, the other should maintain thetemperature until the broken one can be repaired.

Steam distribution pipes.

THIS CHART REPRESENTS A TYPICAL STEAM CURING OPERATION

*T.F. - Tanks Filled**0pened water valve cut-back fuel.

220 U.S. gallons of kerosene was consumedduring steam curing.

NOTE: One generator broke down during thenight. The temperature fell off while the generatorwas being repaired. However, the second generatormaintained the hull temperature at an acceptabletemperature to ensure a good cure.

The peak and the hollow on the graph reflectthis breakdown.

STEAM CURE GRAPH


-

Steamers, fuel, lights and tools.

Adjusting fuel to steam generator.

If the temperature cannot be raised over 120°F(50° C), maintain this temperature for 48 hoursto ensure adequate curing.

Little accurate scientific information ispresently available on the optimum temperatureto be used during the steam curing of ferro-cement hulls. However, if the hull is cured undertemperatures similar to those of the enclosedtable a good job will result.

Pressure and temperature gauges on the steamgenerator.


Steaming in progress.

Thermometers reaching into the hull to registerhull temperature at various points.

Filling shaft housing.

Casting Keel, Engine Beds and RudderHousings

After the steam tent has been removed andthe hull has cooled off, the keel, engine bedsand rudder housings may be plastered.

1) Mix. Use the same mix for plasteringthe above-mentioned areas as was usedfor the hull itself. A slightly higherwater-to-cement ratio may be usedto make the mix more fluid so thatit will fill up the cavities completely.

2) Start at the stem interior and sprinklewater over the stem. This will stopthe hardened concrete from drawingtoo much moisture out of the freshmortar.

Cutting susoension rods.


3) Pack the stem cavity with mortar,vibrating it where possible. Fair themortar into the hull concrete.

4} Work aft through the hull repeatingthe same process. Fill completely thekeel cavity to a height above the gar-board line. Taper the mortar intothe hull.

5) Pour mortar into the engine beds.Insert the vibrator and vibrate thisarea well. Stack the mortar to a heightabove the screeds and leave it to startsetting.

6) Check the rest of the engine roomcompartment. If there are any roughareas apply more mortar and roundoff the corners. When this mortarstiffens it will be steel-troweled smoothto give the concrete surfaces aroundthe engines a slick smooth finish whichwill later be easier to keep clean thanwould a sponge trowel finish.

7) Remove the plates off the rudderstuffing box housing. Pack these fullof mortar. Vibrate them well. Addmore mortar until the housing is over-full. Replace the top plate and tightenup the bolts until the mortar squeezesout from all around the rim. Thiswill form a good seat for the rudderstuffing box gland which will laterbe installed in this housing. As thenuts are tightened up, use a spiritlevel to ensure the top of the plateis finally level in all directions. Thiswill ensure that the stuffing box glandwill not bind on the rudder shaftwhen it is installed.

8) Go back over the stem and keel andsponge trowel finish all the newlyapplied mortar.

Vibrating mortar in rudder housing.

Fitting rudder housing plate.

STAGE 3- JOB 1 VOLUME II Page 65

9) Carefully finish the top of the enginebeds. Smooth the mortar absolutelylevel with the top surface of the T-barscreeds. Clean off any mortar fromthe bolts which protrude. Steel floatthe rest of the mortar.

10) Clean up the tools and equipment.

Mortar is dumped into keel bottom.

Then thoroughly vibrated.

Passing mortar in for the keel. Wetting old mortar prior to pouring new mortar.


Mortar is faired into hull.

Chipping out hair-line cracks.

Mixing waterplug.

Placing waterplug. Engine beds are well vibrated.


Water Testing

If a concrete hull will hold water in, it willhold water out. This is the basic principle of thewater test.

Even with the most conscientious workers,and the best supervision, voids can occur in thehull shell and keels of concrete vessels. Thesevoids, if present, should be tracked down andrepaired prior to proceeding further with con-struction. The best way to date of detectingleaks or potential leaks is to brace the hull welland fill it with water above the load water line.Water will leak out of those same small cracksor voids which will leak when the vessel is inservice. These leaks can be marked on the hulland repaired once the water is pumped fromthe hull.

1) Use a fast-setting cement such as"Quick Plug" (see section on repair)and plug up the drain holes whichwere punched in the bottom of thehull prior to steam curing.

2) Block off the rudder shaft aper-tures and the propeller shaft aper-tures. The best way to do this is toinstall and bed the stuffing boxes intothese apertures. Next, insert the shaftsthemselves and tighten up the stuff-ing box packings.

3) Block any thru-hull fitting holes.Again, the best way to block these isto install the thru-hull fittings andclose the sea cocks. (Note: By install-ing the shafts and thru-hull fittingsprior to water-testing, these fittinginstallations are also tested.)

4) Shore up the hull. If a hull is designedto displace 25 tons when outfitted, itwill hold nearly this amount of waterwhen filled up to the load water line.Be sure the hull is well supported sothat no damage occurs to the hull orthe boat shed floor when this extraweight is placed inside the hull.

Filling hull compartments.

Crane-dropped hull showing damage, cracksleaking and sealing with sodium silicate.

Shoring up for water testing.


5) If the hull contains water-tightcompartments fill these compart-ments one at a time. This willtest if the compartments them-selves are truly water-tight.

6) Pump the water from one com-partment to the next, carefullychecking for leaks and damp spotson the outside of the hull.

7) If small weeps or damp spots occurand the source cannot be recognized,then pour 5 gallons of sodium silicatefor approximately every 1000 gallonsof water into the hull test water. Stirthe sodium silicate (water glass) to besure that it becomes well mixed withthe test water. As water leaks out ofa crack it will carry some of thischemical with it. When sodium silicatecomes in contact with the concrete atthe inside edge of a small crack, itwill form crystals which usually effec-tively seal minor cracks in aboutthree days.

8) If larger, more persistent, cracksappear repair them. (See section onrepairs.)

9) Once the hull is proven water-tight,pump or siphon all the water out.Mop up any standing water andallow the hull to dry out for twodays before commencing outfitting.

Repair

Part 1 — New Construction Voids and Leaks.

Part 2 — In-service Damage.

Grinding rod ends below the surface.

Putting suspension rod ends.


Part 1

A. Sealing Stern Tubes and Rudder StockHousings

Where steel pipe is used for propeller shaftstern tubes and rudder stock housings the follow-ing procedure should be adopted:

1) Chip out the concrete around theentire circumference of the outsideend of the steel pipe in a "V." The"V"-shaped groove should be approxi-mately 1" (25 mm) deep and 1/2"(13 mm) wide at the hull surface.Use a small, cold chisel to do this.Do it carefully so that the "V"-shaped caulking seam is reasonablyneat. Avoid breaking large chipsout of the hull when making thecaulking seam.

2) The builder rolls an even-sized ropeof tarred oakum on his knee in astrip about as thick as a factory-rolledcigarette.

3) Using a caulking iron or a cold chisel,hammer the oakum into the "V"-shaped crack. Pound the oakum intight. Fill the crack to a height ofapproximately 1/4" (7 mm) fromthe surface.

4) Mix up a batch of sealing compound.Use epoxy resin and cement powdermixed together into a stiff consistency.Paint the seam with resin. Then fill itout with the prepared sealing com-pound. The sealing compound canbe smoothed level by the builderwetting his thumb and rubbing it overthe surface.

5) When the sealing compound startsto set paint the area with a coat ofthe same epoxy resin.

Painting over the repair.

Calking shaft log aperture.


B. Sealing Shrinkage and Stress Cracks

If there are any shrinkage cracks whichare obvious to the eye they should be repairedin the following manner:

1) Use a small cold chisel and chip outthe crack in a "V" shape down to theouter layer of mesh.

2) Mix a batch of Roplex, fine sand andcement powder, one part sand, onepart cement, and enough Roplex tomake the mix into a stiff paste orputty.

3) Paint the crack with Roplex. Applythe putty to the crack with a puttyknife or trowel. Paint the surface ofthe crack with Roplex.

4) If the crack is a large one, it may needtwo coats of putty as this mixture willshrink if used in too large an amount.For the second coat of putty repeat thesame process as for the first. Note:Only mix small quantities of putty atone time as this mixture has a shortpot life.

C. Sealing Holes

To seal holes such as drain holes, also smallvoids found under keel support blocks, use thefollowing procedure:

1) Chip away inside the hole so that itbecomes larger than at the surface.

2) Mix up a batch of "Quick Set" or someother fast-setting and expanding patch-ing compound. Roll the compound intoa ball and stuff it into the hole. Smoothout the surface and hold it in place fora couple of minutes until the compoundsets. The plug will expand in the holeand fill it tightly.

3) Paint over the top of the "quick" plugwith epoxy resin. Note: A good epoxyresin to use for patching is a thiokol-base epoxy. "Gluvit" is a recommendedbrand.

D. Sealing Suspension Rod Ends

Where a hull has been suspended from an over-head support during construction, and suspensionrods pass through the deck, the rod ends will remainexposed and level with the deck. These placesshould be treated in the following manner:

1) Clean off the concrete at the base ofthe rods. Use an oxy-acetylene cuttingtorch and cut the rod off as close to thedeck as possible. (Note: heated con-crete will pop and explode. Be sureto wear protective eye-pieces andclothing.)

2) Use a grinder with a carborundum discand grind the end of the steel rod untilit is 1/4" (7 mm) under the surface.Use a lot of pressure and the grindingwill not take long even though it doesmake a lot of dust.

3) Mix up a compound of epoxy andcement (the same as was used for therudder and stern tubes). Fill thegouges left in the deck by the grinder,first painting the gouge with resin,then filling it with putty. Paint theareas with resin to smooth the com-pound level with the surface of thedeck.


Damage cracks to the hull sheer are deepenedwith hammer and chisel into a V-shaped groove.

The V-shaped repair groove is first coated withRoplex, then filled and smoothed with a finesand, cement and Roplex putty.

A large, damaged area to a crane-dropped hull hasthe broken concrete pounded out completely andthe reinforcing steel and mesh faired prior to repair.


REPAIRS IN SERVICE

An unattended fishing vessel is driven ontoremote Bahamian reefs in a storm. Before finallywedging herself on the reef the vessel, her anchorchain parted, pounded her rudder shoe severelyon the rocks. She lay for two weeks on the reef.Later it was found that the propeller shaft, dueto the ferro-cement deadwood having beenpoured solid with concrete, was as true as theday installed. Photos reveal the damage.

The reef-bound vessel from the air.

Damaged steel keel. Minimal damage to ferro-cement deadwood.

Rudder shaft housing driven upwards tnrougnhull shell. The only leak.

Pounding out cracked cement at top of ruddershaft housing.


Part 2

Repair to a Vessel in Service

If a concrete hull receives major structuraldamage while in service it may be repaired asfollows:

1) The vessel should be put into drydock and blocked up in such a wayas to free the area under repair fromstress.

2) All interior fittings should be re-moved from behind the area ofdamage.

3) The damaged concrete should bepounded out from the mesh and steelreinforcing. One man should be sta-tioned inside the hull holding a heavysledgehammer head against the areaof the hull to be repaired. A secondman outside the hull will use a 2-lb.(1 kg) sledgehammer and pound outthe damaged concrete at the pointagainst which the first man is holdinghis sledgehammer head. This will pul-verize the already damaged cementleaving the mesh and rods bare.

4) The mesh and rods should be poundedback into fair. If rods are broken orbadly twisted they should be cut outand new rod lap-welded to the stubends which protrude from the edgeof the damaged area. If the mesh isbadly damaged it should be cut outin this manner:

The outside layer of mesh bothinside and outside the hull should becut back 3" (75 mm) from the dam-aged area. Each successive layer shouldbe cut back 3" (75 mm) further awayfrom the edge of the repair. New meshshould then be cut to the shape of eachpanel and clipped in place. Be carefulnot to lap the joints for this will makethe penetration of the repair mortardifficult if too many layers of meshare built up. Fair the repaired rod andmesh to the lines of the hull.

5) Paint the edge of the repair with asloppy grout mixture (water andcement with no sand). While thegrout is still wet, plaster the repairwith a standard hull mix of mortar.Finish the repair in the same way asthe hull was plastered originally.Lay wet sacks on the inside of thehull and paint the outside of the re-paired area with a concrete sealant.Keep the sacks continually damp for7 days. Paint as with new concrete.

6) Replace the interior fittings afterthe repair has had 7 days to cure.If the damaged area is extensive, donot move the hull for 28 days bywhich time the cure will be complete.

Two-Coat Plastering

Two-coat plastering is an alternative methodto complete plastering in one day or to cold-joint plastering. Essentially, it consists of givingthe entire hull a skin coat of mortar on the out-side all in one day. This outer coat of concretewill be cured and the hull interior plastered at alater date.

The advantages of this method are asfollows:

1) If the plasterers are not accustomed toferro-cement work, in particular, thetechnique of punching the mortarthrough the mesh, then this methodgives the men an opportunity to dothe work in two stages. If penetra-tion was not good enough on theapplication of the outer coat, a chanceremains to succeed with the innercoat.

2) Fewer men are required for thework of applying a single outsidecoat. It is probable that a higherstandard of finish will be obtainedwith this method than with one-daycomplete plastering. The work is thatmuch less arduous and the men, con-sequently, that much more disposedinto putting their energies into obtain-ing a good finish.


Step 1:

The same mixture of mortar is used in two-coat plastering as for other methods. Plasteringprocedure for the hull is also the same with theexception that the plasterers must take specialcare in the hull interior to clean up and removeall mortar which has fallen through the mesh.A stiff broom should be used to brush project-ing mortar back into the mesh leaving the innerlayer of reinforcing rods exposed.

Step 2:

Steam cure the outer coat.

Step 3:

After the outer coat has been steam curedthe inner coat may be applied at the builder'sconvenience. For application of the second coatsupply each plasterer with a bucket of waterygrout. The grout is for flicking onto the imme-diate area he is about to plaster with mortar.The plasterer must force the mortar well intothe mesh, working it thoroughly in all direc-tions, to ensure that every crevice and air pocketbetween the inner mesh and outer coat becomesfilled. When preparing the mortar mix for theinner coat use only medium and fine grades ofsand with a ratio of 100 Ibs. of cement to 125Ibs. of sand. A slightly wetter mix is recom-mended for the inner coat than the mixed usedon the outer coat.

Step 4:

The mortar should be scraped back to themesh and sponge trowelled.

Step 5:

Steam cure the inner coat.

The "Two-Week Plastering Schedule" wouldbe essentially:

Hull - 2 days

Deck - 1 day

Fish-hold - 1 day

Water tanks and keel — 1 day

Bulkheads - 1 day

Skin coat — 1 day

Water test and curing — 1 day

Repair — 1 day

Reserve 1 day for contingencies, totaling tenworking days in a two-week rotating schedule.The above operation refers to a multi-stage plas-tering operation except for the hulls. If the hullsthemselves were to be plastered in stages thefollowing procedure should be followed:

1) After hull meshing and fairing is com-plete divide the hull into two equalsections. Each section should haveapproximately the same surface area.The dividing line chosen would beapproximately the waterline for thepurposes of this example.

2) Cover the area which is not to receivemortar with 4 mil plastic. Fold theplastic at the edge into a neat straightjoint and staple it to the hull woodenmold. This is done to prevent mortarfalling on the mesh which is not to beplastered that day. It will also leave aclean joint for the new mortar when itis applied later.

3) Apply the mortar to the section abovethe waterline which is to be plasteredfirst (the hull is inverted; therefore, thearea of the hull which lies closest to theground). Plaster right over the edge ofthe folded plastic. Cure the area finishedon the first day by brushing on a con-crete sealing compound (any brand nameproduct will do) and allow this to sitfor three consecutive days while thehull cures.

4) After three days remove the plasticsheeting. A neat, clean tapered jointwill be found underneath it. The jointin horizontal areas will taper under theplastic. In vertical areas it will taper awayfrom the plastic. The hull will havegained sufficient strength to carry aman's weight at this time but not suffi-cient strength to be moved. (Notethat the men working on the hull shouldalways wear rubber-soled shoes.) Donot steam cure at this time for there isa danger of warping the rest of thewooden mold.


5) Wet the joint thoroughly. Apply themortar to the remainder of the hullvibrating the joint thoroughly. Becareful not to damage the joint. Asloppy cement grout may be brushedover the joint just ahead of the plas-terers if the builder so desires. It isnot necessary to use any other typeof joint compound other than plaingrout. Sufficient information isstill not available to prove thatcommercial brands of joint compoundplaced between old and new concreteis especially advantageous in ferro-cement work. Grout is cheap andit works well.

6) Finish the joint carefully. When theentire hull has been plastered proceedwith steam curing. The four-dayinterval after applying mortar to thefirst section and steam curing doesnot appear to effect the resultingcure. The steam will wash off mostof the curing compound. Sand-blasting prior to painting will removethe remainder.

Multi-Stage Plastering

The major disadvantage to multi-stageplastering is that the plastering equipment encum-bers the yard for several weeks. With one-daycomplete plastering, on the other hand, theapplication, finish and curing is all over in 72hours. Other work on the hull cannot be car-ried on satisfactorily while plastering is inprogress. Prefabricated components, however,can be made during a drawn-out plasteringperiod. From information gathered to datethere is no apparent structural weakness inmulti-stage plastering providing that themortar is applied and cured properly. Multi-stage plastering is more expensive in a com-mercial operation than is the one-day plas-tering operation. However, multi-stage plas-tering may prove to be more economical toa "one boat off" project. It enables the builderto do a majority of the work himself with theassistance of a few, relatively unskilled laborers.In this way the builder need not employexpensive mortar applicators and finishers.

The main advantage of multi-stage plaster-ing is quality control. If only a small area isto be worked on in any given day by a smallcrew, better control of the mortar penetrationinto the mesh may be maintained.

There are two basic methods of multi-stage plastering. They are: cold joints and two-coat plastering. Cold joints should be handledin different ways depending if the hull is beingbuilt over a wooden mold or with the open,welded framework method.

COLD JOINTS: Framework Method

To best illustrate cold joint plasteringrefer to Volume II, Task 2, page 23, whichdescribes how a 65-ft. (19.5 m) power boat hullwas plastered completely in one day. Alterna-tively, this same hull could have been plasteredusing cold joints as follows:

1) The mesh would not have been appliedto any of the interior members, suchas engine beds, webs and bulkheadsuntil after the hull itself had beenplastered and cured. The weldingwork would be done in these areas,however, prior to plastering. Thestarted rods would all be fabricatedinto the appropriate webs, engine beds,rudder mounts, etc., so that the hullwould receive support during plaster-ing from these members.

2) The hull itself would be plastered first,leaving the deck and interior work untila later date. It would be plasteredinside and out. The area of the hullwhich extends above the deck to formthe bulwarks would only receive askin coat from the outside. Theinside of the bulwarks would be plas-tered and finished at the same time asthe deck. The areas inside the hullwhere the starter rods are fabricatedinto structural members would be fin-ished with a sponge trowel. Then astiff broom would be drawn along theside of the starter rods to form ridgesin the hull mortar. The ridges thenformed would act as a mechanical bond


Houseboat hull built expressly to test multi-stageplastering method. Cold joint is just discernibleat the hull waterline.

between the hull concrete and the weband bulwarks concrete. The broomingmust be done before the hull mortarbecomes too stiff to work. When fin-ishing was complete, standard steamor wet curing procedures shouldfollow.

3) The deck should be plastered at thesecond phase. This would include fin-ishing the inside of the bulwarks andthe hatch coamings. One hour beforeplastering commences the inside of thebulwarks and deck edge would be thor-oughly soaked from a water hose. Thewater should be sprayed under pressureto ensure the mortar along the deck edgebecomes thoroughly wetted. Then themortar may be applied and vivibrated.Particular attention should be given tovibrating the mortar in the deck jointthoroughly. Once the deck is finishedit should be steam or wet cured.

4) After the deck has been cured then themesh can be applied to the interiorstructural members. Once the interiorof the hull has been meshed, the webs,bulkheads, stringers, knees, enginesbearers, floors and rudder mounts maybe plastered and finished and the keelcast. Before plastering begins hatchcovers should be prepared for all thedeck openings in order to retain themoisture from the new mortar curinginside the hull.

Before applying new mortar tothe joint of the hardened hull cementit should be thoroughly wetted. Thesame mortar mix may be used for thehull, decks and the interior. Thesame mix as was used in Task 2, page 23,will prove adequate.

Use plastic sheeting to protect the mesh whileplastering the first hull section.


COLD JOINTS: Inverted Wooden Mold Method

Refer to Volume III where 10 ferro-cementfishing vessels were constructed simultaneously.On a commercial operation such as this, plaster-ing could have been carried out successfully usinga different method, had a continuous produc-tion line operation been set up and completed.The boats were scheduled to be launched, oneevery two weeks, on a year-round operation.The operation could, altenatively, have employedtwo good plasterers permanently rather thanmaintained an eight-man crew which workedone day at a time, then was laid off until thenext hull became ready to plaster.

If two plasterers were to be permanentlyemployed, several hulls could be worked uponsimultaneously. Stripping, meshing interior,deck lining, etc., would be programmed tocoincide with plastering dates. The plasterersand their laborers would transfer from hull tohull daily as each became ready to plaster.

Example of cold-joint plastering, inverted woodenmold method.


Preparing to roll a hull plastered on the multi-stagemethod. Note streaks of curing compound on hullwhich were used to cure the first section plastered.After the second section was plastered, the entirehull was steam cured.

The multi-stage plastered hull shows no sign ofstress cracks at the joints after rolling.

A light sandblasting being given to a hull priorto painting. A better bond is given to the surfaceafter the polished steel trowel finish has beenremoved.


Right:A quick tour of the hull satisfies the men that thereare no leaks. Water-testing prior to launching paysoff.

The 65-ft. (19.5m) hull being towed throughthe locks on her way to out-fitting.

Hull afloat: Ferro-cement does not look handsomeuntil painted. The water reflection pattern is anindication of smooth finish.

The careful use of screeds in fairing the hull sheeris justified when the vessel is seen on the water.

-END OF VOLUME II -

http://www.boatdesign.net/ferro/

u.s. navy ferro- cement boat building manual volume 2

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