zinc coatings

CORROSION MANAGEMENT May 2001

*Nick Karakasch is the principal of Total Corrosion Consultants,Melbourne Australia and specializes in services to the corrosionprevention and structural fire protection industries. He has spent 35years in these industries and has considerable experience withgalvanizing and inorganic zinc silicate coatings. He provides technicalconsulting services to the Galvanizers Association of Australia in thepreparation of specifications and technical detailing.

Many articles have been written covering the meritsof hot dip galvanizing, inorganic and organic zincrich coatings. Much of the continuing discussion re-volves around misunderstandings and anecdotal sto-ries associated with each type. Although some ref-erence to topcoating is made, this article basicallyaddresses untopcoated systems only.

All three systems in discussion are in competitionand are somewhat complementary, each havingstrengths, limitations and selected properties. Eachsystem has its merits for specific applications

The one common ground in the protective mecha-nism is the use of zinc as the means of providing thecorrosion resistance, in particular metallic zinc. It isthe volume and rate of zinc consumption that ulti-mately determines performance together with envi-ronmental exposure and how the zinc is fixed withinthe system.

With inorganic zinc silicate coatings, zinc particlesare surrounded by an inert silicate matrix binder thatslows down zinc dissolution. Likewise, galvanizinghas a similar mechanism in that the corrosion rate ofzinc slows considerably when the alloy layers arereached. It is often assumed that hot dip galvanizingis all zinc, when in fact it consists of four distinctlayers, three of which are zinc / iron alloys.

The corrosion rate for a given volume of metalliczinc regardless of application method is internation-ally documented. It is frequently stated that perform-ance is equal to a given thickness, however all thingsare not equal within each individual system.

It must be strongly emphasised that not only are therewide variations in zinc content but also variations inthickness, uniformity and hardness between coatingtypes, hence the reason for the differences in per-formance. For instance, the volume of metallic zincin hot dip galvanizing is typically three times greaterthan the average zinc filled paint. Likewise waterbased inorganic zincs on average carry 30% more

metallic zinc than solvent based materials and or-ganic zinc rich paints.

The three systems are quite different in their indi-vidual make up and in particular, zinc content. Insome circumstances a combination of systems isused. The ultimate choice will depend on numerousfactors such as; the properties of a particular system,size and structural configuration of the article to beprotected, where, when and how, severity of envi-ronmental conditions and economic factors relatedto expected performance.

A typical example is bridge protection where inor-ganic zinc silicate coatings and galvanizing are of-ten used in combination. Double end dipping tech-niques for galvanizing can accommodate steel mem-bers up to 23 metres in length. However many bridgespans exceed this length or the construction configu-ration is such that inorganic zinc becomes the onlymaterial for consideration. Handrails, guardrails andsmaller components, on the other hand, are virtuallyall galvanized.

Concrete reinforcement bars where used can also begalvanized whereas inorganic zinc coatings are notrecommended for this application. Case studies pub-lished by NACE International have reported the suc-cessful use of hot dip galvanizing under cement fire-proofing materials in the petrochemical industry forperiods up to 50 years with little or no zinc loss.

Inevitably, comparisons are made between systemsthat appear to be selective or unbalanced. For exam-ple, it is often stated that inorganic zinc coatings pro-vide better protection in severe marine environments.In conditions of constant splash, spillage or immer-sion, such as the sea deck on offshore platforms,galvanizing is not recommended unless topcoated.Inorganics do perform better but they also requiretopcoating. Life expectancy is approximately 18months for galvanizing and 24 months for inorganiczinc. In other environments the reverse is the case.

Severe marine conditions, such as the offshore oilindustry, is the one most commonly quoted forcomparative purposes. Galvanizing is confined togratings where the life expectancy on the main deckis 5-8 years, the remaining steel is coated with high

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by Nick Karakasch*


ratio inorganic zinc, that to date has a successful trackrecord of 10 years.

The reason galvanized gratings are used is that theyare impractical to paint with high ratio inorganic zincbecause of their geometrical shape.

Fresh water environments are generally consideredbenign. Inorganic zinc is not recommended for thisapplication as failure occurs within 12 months,whereas galvanizing has a record exceeding 20 years.

Another example is the behaviour of zinc coated steelin buried conditions. Inorganic or organic zinc is notrecommended. Hot dip galvanizing varies in per-formance. Best results are obtained in alkaline or oxi-dising soils where the life expectancy can be as highas 15 years.

Promotional literature comparing inorganic and or-ganic zinc coatings is also often clouded. A case inpoint is the zinc component. A typical claim is thatorganic materials contain 90% zinc compared to 77%or 85% for inorganic. Closer scrutiny shows that thiscan be easily misunderstood or misleading as it re-fers to weight and not the critical component of vol-ume of metallic zinc. While not as user friendly asorganic materials, inorganic zinc silicate coatings,particularly water based products, are clearly supe-rior in corrosion protection. They contain more me-tallic zinc, have better abrasion, temperature and UVresistance.

When top coated the differences are less pronounced.Like galvanizing, both systems have strengths andlimitations. Nevertheless the overall technical fun-damentals clearly favour inorganic materials.

The difference between hot dip galvanizing and zincpaints is in their different nature and their respectivecompositions. A brief description of the major pointsfor each process and the respective characteristicsof the product formed follows.

HOT DIP GALVANIZING (Covered by AS/NZS4680:1999)

Due to galvanizing’s 160 year history, it is the onesystem that has established an unbroken and unprec-edented case history record with virtually no funda-mental change since conception. It is, without doubt,one of the oldest and best documented anti-corro-sive material in the world. Recorded Australian casehistories in a variety of environmental conditionsfrom mild rural, to tropical marine now exceed 110years. Other environments such as marine/petro-chemical exceed 60 years. Retained zinc thickness

in these examples is between 70 to 90 microns.

Galvanizing is not only long lasting but is also pre-dictable in performance to any given microclimate.

The galvanizing process basically involves the dip-ping of steel into molten zinc (450oC) that results inthe creation of a new metal. Zinc silicates and or-ganic zinc rich paints are often misleadingly referredto and marketed as cold galvanizing. Hot dip galva-nizing is synonymous with the protection of steel bydipping into molten zinc creating a zinc/iron alloy.

The secret of galvanizing is in the volume of zincthat alloys to the surface and the corresponding hard-ness. The zinc is actually alloyed to the steel there-fore contact between zinc and steel is at the “atomiclevel”. Even when the steel has been damaged it isimpossible to separate zinc from steel. One reasonfor this is that hardness ranges from 70dpn (diamondpyramid number) for the top zinc layer to 240dpn.The so-called delta layer at 240dpn is considerablyharder than 250 grade steel that is typically 160dpn.

The hardness means that galvanizing provides abra-sion resistance superior to any known zinc paint coat-ing. Regardless of the type of zinc paint, they stillremain surface coatings only and are not integrallyalloyed to the steel substrate. Taber abrasion testsby the eminent Dutch corrosion authority Jan VanEijhsbergen revealed that epoxy zinc-rich primertaken as unity showed that polystyrene zinc-rich are5 times better, zinc silicate 50 times better and hotdip galvanizing 500 times better.

The thickness or zinc mass achieved depends largelyon surface condition, composition, zinc temperature,immersion time, mass and thickness of the steel be-ing galvanized. As steel sections increase in mass /thickness so accordingly does the end result in termsof zinc/alloy thickness. The Australian Standard AS/NZS 4680:1999 nominates ‘minimum’ thickness forsteel sections. For example above 6mm, 85 micronsis quoted, however in practice it is considerablyhigher due to the nature of the process. Actual filmthicknesses will range between 95-200 microns, wellabove the nominated minimum.(Fig 2).

Another major advantage of galvanizing is the extragrowth on all edges and corners that occurs duringthe process. It can be said with confidence that themajority of failures with paint systems invariablystart on corners and sharp edges.

Another benefit with galvanizing is that all surfacesare treated, whereas by contrast, control of manualpainting is difficult. Even experienced paint appli-


cators have difficulties in maintaining uniform thick-ness and applying paint materials to hard-to-get-ar-eas. Two sided protection is also an important con-sideration. Manual application techniques are notsuitable and cannot coat the internal surface of hol-low sections that would in turn give rise to inside-out corrosion.

The greatest advantage of hot dip galvanizing is thaton removal from the zinc bath the process is fin-ished and components can be handled through toerection without the risk of damage. By contrast allzinc paint alternatives require specific curingconditions and sustain damage to varying degrees,that regularly translates to construction delays andsite repair costs. Site repair of paint coatingsfrequently becomes evident late in construction asan added variation expense to the end client. No sitetouch up of galvanizing is necessary unless weldingor drilling takes place.

The process of galvanizing is basically mechanicalhandling. It is inherently simple and has changed lit-tle since first described in 1837. The use of galva-nizing does require attention to detail during thedesign and specification stage to ensure favourabledesign criteria. Distortion of fabricated sections canoccur if basic design guidelines are not followed.

The inspection process is fast, simple and requiresminimal labour. The fundamentals of the process aresuch that galvanizing will not occur if the steel hasnot been properly cleaned. That is immediately evi-dent. Therefore, the opportunity to conceal inad-equate surface preparation is non existent.

The application of topcoats to galvanized surfaces isusually for identity, aesthetics or added chemical orcorrosion resistance in extreme service.

ZINC FILLED COATINGS

There is an extensive range of zinc rich paintsavailable, all based on individual formulations. Per-formance varies widely due to varying zinc contentand binder type. Zinc depletion is not easy todetermine and can only be calculated by the use ofzinc coupons or by laboratory techniques.Performance predictability to any given microclimateis difficult to assess. Accelerated testing of zinc paintsonly provides a guide to performance. Correlationto real service exposure is not easy to determine andremains a challenge to the paint industry.

Zinc coatings are divided into two broad classes bythe type of resin or binders used.

One class is called inorganic. These use binders thatare substances of inorganic nature i.e. based on ma-terials other than carbon chemistry.

The other type is called organic zinc rich primer.These products have binder/resin systems that are oforganic nature i.e. based on compounds of carbon.Whilst there is some technical similarity, the majordifference is that inorganic binders do not suffernormal degradation as with organic binders, are con-siderably harder and have greater volumes of zinc.

Industry promotional activity has tendered to be gen-eral, suggesting that all inorganic zinc paints areequal in performance regardless of type. Experiencehas shown there are distinct differences in perform-ance between types. The heat and chemically curedmaterials were without doubt the best performers.However these products are obsolete and have beensuperseded by materials that do not have the sameperformance characteristics and are somewhat infe-rior in comparison.

There is no doubt that inorganic zinc silicate coat-ings in the paint industry are excellent products andare the acknowledged leader in combating corrosionas single coat applications, or as primers for highperformance topcoats. Their use has been wide andvaried with outstanding results. The application oftop coats is usually only necessary in areas of ex-treme chemical fallout, immersion conditions suchas fresh or salt water, concrete encasement or to im-prove the aesthetic appeal.

Adhesion of zinc paints to the substrate is predomi-nantly mechanical, that is determined and influencedby the degree of surface preparation and roughnessobtained. Minimum surface preparation necessaryis class 2.5 or 3 (near or white metal) AS1627.4 1989.

INORGANIC ZINC SILICATE (Covered by

AS/NZS3750.15:1998)

There are numerous types of inorganic coatings eachwith advantages and disadvantages that would makethem the first choice for a particular application.

Inorganic zinc silicate coatings consist of zinc dustin finely divided particle size form dispersed in avariety of mediums bound in a matrix of silica. Thereare four basic types: heat and chemically cured, andtwo self curing materials based on either water orsolvent. The heat and chemical cured materials arenow obsolete, and have been superseded by the self-curing water and solvent based materials.

Whilst the binder systems may be either water or


solvent, the final chemical structure is similar on fullcuring. Water based materials on average carry 30%more metallic zinc, and have better abrasion andtemperature resistance. Nevertheless thesecharacteristics are being ignored by sections of thecorrosion industry that now claim or suggest thatsolvent borne zinc is equal.

For the purposes of this article, four commercial in-organic zinc products were selected at random andevaluated by independent authorities for metalliczinc. The evaluation showed that only one materialappeared to meet the criteria outlined in the Austral-ian Standard.

The evaluation for metallic zinc showed clearly thatthere are a variety of formulations available, someof which do not comply with the pigment constituentsspecified for zinc dust in AS/NZS 3750.15:1998,although it must be emphasized that not all productsare marketed as conforming to this standard. The non-conforming materials with variations are shown inFig 3.

Fig 3

Note: AS/NZS 3750.15:1998 “The zinc oxide content may becalculated as the difference between total zinc content and themetallic zinc content multiplied by 1.25”.

WATER BASED

This coating type is without doubt the best of thezinc coatings available. It is characterised by fasthardening, good damage resistances, and higher me-tallic zinc content in the dry film. It is sensitive tohigh humidity and low temperatures during theapplication stage.

The curing time is two to three hours but is dependanton climate conditions. It has non-toxic, non-flam-mable properties and early hardness permits rapidhandling of coated steel. Being water based, it hasno EPA restrictions. While its usage has been varied,its main use has been in the offshore oil industry and

for road and rail bridges. The offshore industry, inparticular, has demonstrated the advantages of waterbased materials over solvent based materials, thatare totally excluded from this applicationenvironment.

SOLVENT BORNE (ETHYL SILICATE)

These materials are available as either two or sin-gle-pack and have been the dominant materials usedin the paint industry. They are characterised by tol-erance to high humidity and low temperature appli-cation but are slower to develop handling resistanceand do not fully reach the ultimate hardness of thewater borne type.

They are best suited for site application under diffi-cult weather conditions. Metallic zinc content andabrasion resistance is lower than water based mate-rials. It is for technical reasons that the same highloading of metallic zinc cannot be incorporated as inthe water borne type without some loss of film buildproperties, abrasion resistance and ultimate life. Thisloss ranges from marginal to substantial when com-paring some lower cost materials available. In addi-tion, they are solvent based and therefore are not asenvironmentally friendly as their water based coun-ter parts.

ORGANIC ZINC RICH COATINGS

(Covered by AS/NZS3750.9:1994)

Most types of organic resins have at one time or otherbeen used as zinc rich primer binders. Organicbinders are film formers and have the tendency toencapsulate and insulate individual particles of zinc.Binders used have been such resins as; epoxy,chlorinated rubber, phenoxy, epoxy ester, urethanealkyd and polyester, to name a few.

Main advantages are greater tolerance to poorer sur-face preparation, ease of application, better flowcharacteristics, greater film flexibility, ease of topcoating as they contain no voids, slightly better curingin low humidity conditions and some chemicalresistance.

The down side is they generally cost more. The tradeoff is that surface preparation and application labourcost is less, they contain less zinc, are lower in UV,temperature and abrasion resistance, generate morewelding fumes and performance expectations areconsiderably less. These materials usually providesome initial galvanic protection because the highweight loading of zinc affords some zinc to zinc con-tact. With time they tend to behave and function more

C h em ic al C om p o sitio n of Z in c D ust S a m ple s w t %

P r od u ct T y pe Z inc( T o tal )

Z inc(M etal)

Z inc(O x id e )

P B F E C D

T y p e 4 S olve n t 94 .5 80 .3 14 .2 0.04 < 0. 01 < 0. 01

T y p e 4 S olve n t 93 .8 82 .9 10 .9 0.04 < 0. 01 < 0. 01

T y pe 6H igh R a tioW a te r

98 .7 80 .1 18 .6 0 .0 10 < 0. 01 < 0. 01

Z in c D ust as p e r A S/N Z S 3 7 5 0. 15 . 1 9 98

Zinc D ust 9 8. 0 m in 9 4. 0 m in 5 * 0 .2 max 0.05 ma x 0 .1 max


like conventional type primers, rather than providingtrue galvanic protection as with inorganic zinc paints.For these reasons they are generally used in ‘systems’rather than being left un-topcoated.

Inorganic zinc primers provide much better protec-tion, particularly water based materials. They have agreater ability to carry a higher volume of zinc in thedried film. The reason for this is the higher densityof the silicate binder. The average organic zinc with90% zinc by weight only translates to approximately60% by volume, due to the different densities be-tween silicate binder and epoxy resin.

To illustrate the point the following typical examplecompares total zinc loading of 90% by weight of or-ganic to inorganic in a direct comparison. In prac-tice the weight of zinc varies in accordance with therespective standard.

Fig 1

Water based inorganic paints have the highest vol-ume loading of metallic zinc of any applied zinc paintcoating.

Note that both have 90% by weight in the dry film,however the inorganic has 77% zinc by volume(12.60 divided by 16.45) whereas the organic coat-ing has only 59% (12.60 divided by 21.28) zinc byvolume, a variance of 23% in this example favour-ing the inorganic zinc. Again the difference arisesfrom variations in density, giving inorganic coatingshigher volumes of zinc in the dry film. The key pointin any comparison between coating types is metallicvolume of zinc, not weight.

Higher zinc by volume allows for more intimate zincto zinc, and zinc to steel contact. Because of the rela-tively higher amount of binder present in the organicversion, the zinc is more insulated and inhibited fromproviding cathodic protection to the steel.

The respective Australian Standards quote “metal-

lic” zinc contents as; 77% for solvent borne inor-ganic, and 85% for water based inorganic. Organicprimers are nominated as total zinc mass of 85-94%.When total zinc is quoted it includes non-metalliccomponents such as zinc oxide. Only metallic zincis capable of providing galvanic protection. Inorganiczincs clearly carry more zinc by “volume” due tothe differences in binder densities. Metallic zinc byvolume should be the major consideration in anyevaluation process.

The current wave of marketing appears to favourepoxy zinc rich primers over inorganics, particularlyin comparison to solvent borne types that are clearlysuperior in performance as single-coat materials.Water based materials are rarely mentioned in anycomparison although they are superior to both of theother two. It would appear that formulated charac-teristics of organic materials favour application tech-niques and speed rather than higher corrosion resist-ance.

The movement amongst some manufacturers in pro-moting organic zinc rich primers has clear manufac-turing cost advantages. This can be evidenced by theprocessing of 100 kilos of base raw materials for bothproducts. The end result in manufactured volumeclearly favours organic materials.

INSPECTION

Inspection of paint systems is somewhat complex,AS/NZS2312:1994 (Guide to protection of iron andsteel against exterior atmospheric corrosion) sets outthe requirements and practices needed to ensureproper application. Inspection costs are often overlooked. It is generally accepted that inspection costsof 2-8% of the total job should be viewed as a pre-mium on insurance against the cost of rectifying pre-mature coating failures. Many coating failures canbe traced back to questionable practices during sur-face preparation and application.

The main areas of coating inspection for all steelprojects are:

· Specification enforcement and job controlmaintenance

· Job process monitoring and regulation

· Interfacing with engineer and contractor’s rep-resentative

· Responding to extraordinary conditions

· Surface preparation (pre-blast washing, beforeand during operations)

Z IN C C O N T E N T C O M P A R IS O NO R G A N IC V S IN O R G A N IC

O r ga n ic In or ga n ic

W e ig h t V olu me W e ig h t V olu me

B in d e r (e pox y) 9 8 .1 8 10 (S ilic ate ) 3 .8 5

A d d itive s 1 0 .5 0

Z in c D u st 9 0 12 .6 0 9 0 12 .6 0

10 0 21 .2 8 10 0 16 .4 5

Z in c C o n te n t 90% 5 9 % * 90% 7 7 % *

D e nsity used to c onve rt to vo lum e: Epox y B ind er 1 .1 , A dd itive s 0 .5 , Inorga nic S ilic a te sB ind e r 2 .6 , Z inc D ust 7 .1 4


· Priming and pretreatment coats (before andduring operations)

· Intermediate, mid or tie coats (before and dur-ing operations)

· Finish coats (before and during operations)

· Record keeping

In summary, inorganic materials should be consid-ered where high performance is required. In less se-vere environments or where adequate surface prepa-ration is not achievable, organic zinc rich paintswould be more appropriate. Organic zinc materialsare outstanding products as touch-up(site) materialsfor inorganic coatings or galvanizing. They make agood compromise although thickness needs to be in-creased to compensate for the lower zinc content.

As single coat applications, inorganic materials areclearly superior, particularly when water based. How-ever where top-coats are necessary the distinction isless and in many circumstances will actually favourorganic zincs.

COST CONSIDERATION & COMPARI-

SONS

The cost comparisons between systems are gener-ally not well understood. Confusion arises from thedifferent pricing methods used. Galvanizing is typi-cally charged by weight whereas zinc rich coatingare calculated on surface area.

Whilst there are always exceptions, average pricesare often extrapolated in an over simplified way onassumptions that unit prices would remain the samedespite being applied to a vast range of sizes andweights.

Because of the current demand for productivity andsite time efficiency, primary installation costs needto account for such items as:

· Radius or chamfered edges· Repairing transport damage· Quality controlled inspection· Erection damage repair· Total effect on site occupation

Site repair, inspection and radius or chamfering ofedges where necessary have a significant impact ona project and therefore should always be part of anyevaluation process. Unfortunately this is not alwaysthe case and they are seldom costed. There is also acumulative effect with regard to much greater costsin future maintenance unless a disciplined repair

schedule is undertaken.

To examine and illustrate final installed costs, thefollowing costs are expressed in square metres anddetail first cost, inspection, and estimate site repaircost. These were obtained from the market place andare typical only. These extra costs are conservativeestimates and don’t take into consideration extra stag-ing required, delay to other trades or site penalty ratesthat may be applicable.

Fig 4

Notes:

System 1

Hot dip galvanizing average price $455 / tonne

(Assume steel sizes of light – medium, heavy – average 24 m2 / tonne)

$18.75 m2

System 2

Radius / Chamfer Edges

$120 / Tonne

(Assume 25 lm / Tonne)

Price quoted is conservative and includes extra handling.

H o t D ip G a lva n izin gAverage p rice $4 55 / tonneAssum ed ligh t, me d , a nd heavy stee la verage s urface a re a per to nne 2 4m2

$18 .75 m 2

O R

Inorgan ic Z inc (Type 3 /6 wate r based) 125- 50microns

$20 .00 m2

Initia l app lic ation inspe ction (2 -8 % ) say 5% $ 1 .00

S ite re pairs 5% $ 1 .00

S ite inspection $ 1 .00

$23 .00 m 2

Plus app licab le site pe nalty rate s sc affo ld ing o r s taging

TYPICAL TOTAL COST COMPARISON

Long-term Protection

The Premise: 5000 Tonne Steel (24m2 surface area /tonne) 120000 m2

System 1Hot Dip Galvanizing

System 2Inorganic Zinc Silicate

(type 3 or 6)

Radius / Chamfer Edges NIL $600,000

Initial cost of Application $2,275,000 $2,400,000

Initial Inspection 5% NIL $120,000

Site Repairs 5% NIL $120,000

Plus Site Penalty -scaffolding or staging

NILRequired / Cost

unknown

Site Inspection - $120,000

TOTAL INITIAL COST $2,275,000 $3,360,000


CONCLUSION

Most hot dip galvanizing is accomplished withfabricated components prior to erection. Smallcomponents are much easier to galvanize, particularlyintricate items.

Zinc paints were originally developed to overcomethe limits of galvanizing bath sizes. They offer flex-ibility in use, particularly for large and complexitems. They are generally suited for in situ applica-tions or where complexity of steel structures is suchthat it suits painting. The shipping and maintenanceindustry, together with large storage vessels are goodexamples of where zinc paints are highly suited.

This article has attempted to offer a comparison inthe use of un-topcoated zinc coatings and galvaniz-ing and to give basic guidance as to the merits ofeach process. Choosing one system over another orin combination is not always simple, but not neces-sarily difficult providing the evaluating authority isaware of the differences involved.

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REFERENCES

• Australian / New Zealand Standards:- AS/NZS 3750.9:1994 Organic Zinc Primers- AS/NZS 3750.15:1998 Inorganic Zinc Silicate Paint- AS/NZS 2312:1994 Guide to Protection of Iron and Steel

Against Exterior Atmospheric Corrosion- AS/NZS 4680:1999 Hot Dip Galvanized (zinc) Coatings

on Fabricated Ferrous Articles- AS1627.4:1989 Abrasive Blast Cleaning

• Corrosion Resistance Galvanized Coatings RetrospectiveEvaluation: - A.J Vazquez & J J DeDamborenea, CentroNacional De Investigaci - ones metallurgical (cenim / csic),Spain

• Coating Guide for New Steel Bridges, Szokolik ConsultingPty Ltd, November 1999

• L Vincent, Corrpro Companies Inc USA, PMC ArticleSeptember 1999

• Hot Dip Galvanizing Journal, Dr M Burcher, 1993

• Facts About Inorganic Zinc Coatings, N Karakasch, March1999

• Nace International, Corrosion 94, Paper 521

TYPICAL COMPARISON CHARTHOT DIP GALVANIZING - INORGANIC ZINC SILICATES

USE OFAPPLICATION

GALVANIZING INORGANIC ZINC SILICATESOLVENT BORNE WATERBASED

Inspection Minimal (selfinspection)

Reqs Continuous Inspection

Dry Film ThicknessControl (including edges)

Excellent Needs Care Edges & CornersNo

Coating Thickness 85 microns180 microns

75 microns 150 um

Zinc Mass /m2 (average) 600 gms/m2 185 gms/m2 560 gms/m2

Adhesion Fusion Bonded Surface Coating Surface Coating

Hardness 8 x Harder ThanZinc Paint

- -

Site Touch After Erection No Yes Yes

Weather / Curing Delay No Yes Yes

Temperature Resistance 200oC 300oC 400oC

Chemical Resistance ph 6 - 12.5 6 - 10 6 - 10

Salt Water Immersion No No No

Environmental Cleanliness Yes No - Contains VolatileSolvents

Yes

Site Application No Yes Yes

Fresh Water Immersion Yes No No

Buried Conditions Yes No No

Concrete Reinforcement Yes No No

ZINC COMPARISONGALVANIZING & ZINC RICH PAINTS

GALVANIZING

STEELTHICKNESS

AS/NZS MINIMUMSTANDARDTHICKNESS(MICRONS)

ACTUALAVERAGE DRY

FILM THICKNESS(MICRONS)

METALLICZINC

CONTENT(gm/m2)

3mm plate 55 99 707

4mm plate 70 110 785

5mm angle 70 110 785

6mm plate 70 130 1000

12mm plate 85 150 1070

200 UB 85 140 1000

310-410 UB 85 150 1071

Heavy StructuralSteel

85 180-200 1285-1428

180-200 PFC 85 120 857

125-150 PFC 85 110 785

RHS/SHS (light) 85 85-95 607-678

ZINC SILICATE PAINT SYSTEMS

Steel ThicknessThickness for all steel sections is constant. Metallic zinc is data from governmentaltest.

AS/NZSZinc Content

StandardThickness

Metallic ZincContent gm/m2

Inorganic(Solvent)

77% of Dry Film (metallic) 75 microns 185

Inorganic (Water) 85% of Dry film (metallic) 75 microns 289

150 microns 578

Organic Zinc Rich(epoxy)

90% Zinc Content 75 microns 185 *

zinc coatings

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