REPAIRING PLATING ROOM FLOORS by Walter Lee Sheppard, Jr.

CCRM Inc., Havertown, Pa.

Every plater is faced at one time or another with the problem of repairing or replacing the floor in his or her plating room. The plater wants to do it as quickly as possible so as to get back into production with the least downtime, yet to make a repair that will last. This is particularly important where there is automatic machinery---where plating racks are lowered, timed, and raised in an automatic cycle, and deterioration of the floor can make a tank tilt out of alignment and cause the rack to hang up on a tank wall.

In the past, small plating shops have made do at the start with an existing floor in a converted residential building where the floor is often of wood. Consider the problem that may exist with the heavy standing load of liquid-filled tankage on floors that were designed to support people and their furniture. The first thing to do is to check the beams and supports to be certain that their design is adequate and condition sound. A local contractor or engineer friend can do this for you at minimum expense and it is of key importance to your success. The engineer should consider inadequate any floor that will deflect visibly under the load that you expect to place on it. It is acceptable to f ee l movement as long as you cannot see it.

If the tanks are placed so that liquid dragout on the work or racks drips on the wood floor, no amount of washdown can save the floor from serious damage. If you have tried operating without a protective surfacing over your floors, you have already discovered this, and you may have also discovered damage on the floor below caused by !eaking from the operations.

The best protection, if your floor supports are strong enough, is to cast a 4-in. reinforced concrete slab on top of the existing floor, and apply a preferably thin (ll/4-in.) acid-brick floor over the concrete, employing a hot asphalt membrane between the concrete and the brick. (See article on Acid Resistant Floor Construction elsewhere in this Guidebook.) The second choice is a V4-in. trowelled epoxy floor surfacer over the concrete. Be careful to install a proper drain in the concrete and to slope the surface to it. A polymer concrete may be an acceptable substitute for both the concrete and the topping.

If the existing floor is unable to support the weight of the concrete in addition to that of the loaded tanks, all is not lost. There remains a compromise, which if properly installed and maintained, can last for many years. Clean the old wood floor thoroughly, replacing any damaged or badly worn timber. Then, bring in a large sander and run it over the old floor to get a completely uniform surface. Now nail down over the old wooden floor sheets of s/s-in. thick or thicker marine plywood, butting all the edges tightly and smoothly together, and countersinking all nails. Over the marine plywood apply, as first choice, a hot asphalt membrane and 21/4-in. (not thinner) acid-brick. Expansion joints should be placed at 15 ft. intervals or less.

If this is beyond the weight limitations, then the'second choice is a V4-in. thick epoxy surfacer. If the epoxy is used, place expansion joints around the periphery of every sheet of plywood, matching the expansion joints to the cracks between that sheet and the next. Both types of floors have served successfully for years over this type of substrate, provided that they are properly cared for and maintained. This means repair as soon as a crack appears. Do not delay.

If the floor under the duck boards is plain concrete, or concrete protected only by a paint coating, and has been subject to spills and drips for a long time, the damage will be extensive and will cover the entire working area. Under such circumstances, there may be such smactural damage to the building as to make repair a waste of money, or so much plating waste may have penetrated the soil under the floor as to cause problems with the EPA. In either case, excavation of the diseased concrete and of all badly contaminated soil must be accomplished before the work area can be rehabilitated.

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Fresh concrete, properly designed and reinforced, is then installed, with the reinforcing tied in solidly to the reinforcing in the walls and elsewhere in the building. Before considering measures to protect the new concrete from experiencing a repetition of this damage, the concrete must be permitted to cure, free of traffic, or the spillage of any corrosives. The use of type III Portland cement in the mix will provide acceptable strength in four days. However, faster strength development and readiness to accept the corrosion resistant surfacing can be more quickly supplied by the use of a super plasticizer in the concrete, while simultaneously retaining "slump" at a maximum of 4 in. With the appropriate amount of super plasticizer added and using type I Portland, full strength (not just a workable percentage) will be developed in 72 hours, and with a reduction of 30-32% of water demand. In 28 days, the concrete will develop a 190% design strength and the low absorption of 5-6% as compared with "normal" concrete absorption of approximately 20%.

If this route is followed, the new concrete surface should be decreased by the thickness of the surface protection planned. With an acid brick, this would be 25/8 in. (including 1/4 in. for an asphalt membrane plus 21A-thick shale brick with a 1/8-in. bed joint of mortar). Lesser thickness of brick may be used if desired, but labor and material costs will not be much different if 11/8-in. red shale splits or 11,4-in. pavers are used, and the delivery time may be longer. Do not go under 1 in. thickness and do not use quarry tile. With a polymer concrete, the same general construction may be accomplished.

If a l/4-in, epoxy monolithic topping is used, the change in elevation is slight, but the 1/4-in. slope to the foot required in this case may affect the location of services if the original floor is dead flat.

If the floor of the shop is new, or if the shop has only been operating for a short time without floor protection, it would be wise to arrange for floor protection at the earliest available time, closing off and working on each individual area in turn. If the work is to be done in this manner, the least downtime will be experienced if castable floor surfaces 1- to 2-in. thick are planned to cover the existing floor. This will mean elevating all services, electrical and plumbing, in each area. That work may be done at the same time the floor contractor is cleaning the surface of the floor that is to be elevated, before applying the new surfacing.

Though an acid brick floor properly selected and installed is the best protection you can get, it would require at least double the downtime of the monolithic surfacing and would necessitate further elevation of the services.

Inasmuch as no castable monolithic or polymer concrete can tolerate exposure to the full range of corrosives in a plating shop, it is important to plan to segregate your operations and assign specific areas for specific exposures. All chrome work, where there is a possibility of chromic acid spillage, and all areas where nitric acid over 5% concentration may be spilled, should be grouped and, if possible, done simultaneously. A castable polyester or vinyl ester mortar with acid brick, or a polymer concrete made from these same resins, is the type of material indicated in such a case.

In areas where any acids other than hydrofluoric are used and/or where caustics may be spilled, a fnran concrete may be selected. In areas where spills may consist of strong bleach, weak acids other than hydrofluoric, mixed perhaps with any combination of caustics, epoxy concretes are indicated.

Where hydrofluoric acid or strong alkali exposure are anticipated, the same resins may be used as just mentioned, but the filler must be carbon, such as crushed anthracite.

Recently, there has been an intensified interest in the use of sulfur concretes in plating shops. The plater should be warned, however, that copper and beryllium salts react very slowly over a period of a year or more with sulfur concrete and sulfur cements to form expanding growth salts, a reaction that can eventually destroy the floor. In such areas, brick mortared with sulfur cement or a sulfur concrete obviously should not be used. It should also be noted that sulfur mortars and concretes can be injured by exposures for any extended periods to live steam.

A great many sales pitches and much advertising accompanied by case histories have

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appeared in technical literature over the past decade, pushing the use of silicate castables as floors in chemical areas. They often claim satisfactory operation in areas of exposure to everything except hydrofluoric acid and acid fluorides, within a pH range 09 , sometimes even 0-12.

The plater should receive these claims with caution. Although it is absolutely true that silicate castables and silicate concretes have outstanding resistance to all acids except hydrofluoric (and acid fluorides), when subjected to alkalis in a continuous exposure they will be quickly damaged and, in a short time, destroyed. Silicates resist organic materials with pH ranges as high as 9, and for a short period of time the bases of weak alkali metals. Even very dilute solutions of hydroxides of the strong alkali metals (sodium, potassium, and so on) attack them very rapidly. Continued exposure to live steam and to running hot neutral or alkaline water will wash them out.

Further, silicate castables (or silicate concretes) have far higher fluid absorption than other polymer type concretes. To be used satisfactorily in plating service, they should only be employed over positive liquid seal membrane. Without the membrane, liquids standing on them or passing over them will eventually penetrate to the substrate below, and although they may not damage the silicate castable, the penetrating materials still have the power to damage the substrate. With the limitations just stated, silicate castables may be considered for use in a few specific areas.

Note that all polymer concretes are subject to hairline cracking over long periods of time. If a crack should occur it must be repaired promptly if the floor is to survive.

Electroplating of Zinc Diecastings by S.K. Jalota 225 pages $90.00

This b o o k p rov ides a qu i t e exhaus t ive coverage of p la t ing on z inc die castings s ta r t ing w i t h design and p r o d u c t i o n w i t h emphas is on its rela- t i on to p la t ing. Subsequen t chapters t rea t po l i sh ing , buff ing and mass f inishing, c lean ing and p r e t r e a t m e n t , and the e q u i p m e n t fo r plat ing. T h e balance o f t he b o o k runs the gamut of t he var ious metals that can be deposi ted . Each chap t e r devo tes a p o r t i o n to t roub le shoo t ing , caus- es of defects, and remedies . C o n c l u d i n g chapters conce rn color ing , lac- quer ing , s t r ipp ing of deposi ts , and analysis and testing.

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