Surface Prep App Guide

8/9/2019 Surface Prep App Guide

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P e r f o r m a n c e

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S U R F A C E

P R E P A R A T I O N

& A P P L I C A T I O N

G U I D E



P a g e

S u r f a c e P r e p a r a t i o n 3

o f C a r b o n S t e e l 4

o f D u c t i l e a n d C a s t I r o n 6

o f S t a i n l e s s S t e e l 7

o f G a l v a n i z e d S t e e l a n d O t h e r N o n - F e r r o u s M e t a l s 7

o f C o n c r e t e a n d M a s o n r y 7

o f P l a s t e r 9

o f G y p s u m D r y w a l l C o n s t r u c t i o n 9

o f W o o d 9

o f P r e v i o u s l y P a i n t e d S u r f a c e s 9

A p p l i c a t i o n G u i d e 1 0

F i l m C h a r a c t e r i s t i c s ( T a b l e V I ) 1 4

T A B L E O F C O N T E N T S



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Most surface preparationand application operations requirethe use of appropriate personalprotection equipment and

engineering and administrativecontrols. The most obviousexamples of this are abrasiveblast cleaning and spray paintingoperations. It is incumbent uponthe coatings and abrasive blastcleaning contractors to ensure thatall personnel are properly protectedfrom all hazards.

Numerous OSHA regulations specify when, where and how workers areto be protected. These regulations,the coatings and equipmentmanufacturers, and/or local OSHAofficials should be consultedas necessary to ensure properprotection, compliance with thelaw, and to avoid liability issues.Can labels and Material Safety DataSheets should always be consultedprior to coatings operations.

Safety and health details shouldbe addressed prior to implementing these operations.

Each year millions of dollars are wasted on good coating systemsthat will fail prematurely due toinadequate surface preparation orimproper application. Much of this

waste is needless and can be

prevented through proper evaluation, specification, and control ofthese two vital factors. Theintent of this portfolio is to

offer basic guidelines enabling you to maximize your coatingexpenditure. The informationpresented has been accumulatedfrom outside technical reports andpublications, as well as Tnemec’sown research and experience inthis field.

SURFACE PREPARAT ION ANDCOAT ING PERFORMANCE

Coating performance is dependenton adequate surface preparation

and application. Properly writtenpainting specifications incorporatesurface preparation and applicationprocedures as an integral part ofthe coating system in recognitionof this fact. This guide is designednot only as a basic reference tomodern surface preparation andapplication methods and procedures, but as an aid in selecting the proper type of surface preparation andapplication for a particular designrequirement or service condition.

COST OF SURFACE PREPARAT ION

The major cost of a coating system is not the coating material itself,but the cost of labor for surfacepreparation and application ofthe coating system. The costbreakdown of a typical coatingoperation will normally fall withinpercentage ranges listed in Table I:

TA BLE I - CO AT I NG S YS TEM

Application Labor 30 - 60%

Surface Preparation 15 - 40%

Coating Material 15 - 20%

Clean-up Labor 5 - 10%

Tools and Equipment 2 - 5%

In recent years, both applicationand surface preparation costshave escalated much more rapidlythan the cost of coating materials.It is estimated that labor costs

will continue to increase fasterthan materials and the differencebetween the two will, therefore,become even greater. These costfactors further underscore theadvisability of evaluating, specifying and controlling the surface preparation

and application on every coatingproject where high performance and long-term protection are expected.

S U R F A C E P R E P A R A T I O N



SURFACE PREPARATION

OF CARBON STEEL

The surface preparation requiredfor different types of coatingsystems to be applied over carbonsteel will vary considerablydepending on the type of coating

as well as the service environment.The Society for Protective Coatings(SSPC), NACE International (NACE),

American Water Works Association(AWWA) and the American Societyfor Testing and Materials (ASTM) allmake reference to various standardsthat define degrees and methodsof surface preparation. The most

widely used surface preparationspecifications are those publishedin Steel Structures Painting Manual,

Vol. 2, Systems and Specifications.Given below is a brief description

of the various SSPC/NACE jointsurface preparation standards. It isrecommended that you refer to theSSPC or NACE standards for thecomplete text of the specifications.

SSPC-SP1 SOLVENT CLEANING

The removal of all visible oil,grease, soil, drawing and cuttingcompounds and other solublecontaminants from surfaces; withsolvents or commercial cleanersusing various methods of cleaningsuch as wiping, dipping, steam

cleaning or vapor degreasing.It is generally conceded that

wiping with solvents will notpositively remove all oil, greaseand other soluble contaminantsfrom the surface. Therefore, amore efficient cleaning methodsuch as vapor degreasing or steamcleaning should be employed

where coatings will not tolerateany oil, grease and other solublecontaminants residue.

Oil, grease and other soluble

contaminants removal by solventcleaning is precluded in allother SSPC/NACE SurfacePreparation Specifications; it is notnecessary to cite SSPC-SP1separately when a higher level ofpreparation is specified.

It should be noted that organicsolvents may not remove watersoluble contaminants such as acidand alkali salts. Such contaminantsshould be removed using water

and/or water-based cleansingagents. Reference SSPC-SP COM.

SSPC-SP2 HAND TOOL CLEANING

The removal of all loose millscale, loose rust, loose paint andother loose detrimental foreignmatter by the use of non-power

hand tools. Hand tool cleaning willnot remove adherent mill scale,rust and paint. Mill scale, rust andpaint are considered adherent ifthey cannot be removed by lifting

with a dull putty knife.

SSPC-SP3 POWER TOOL CLEANING

The removal of all loose millscale, loose rust, loose paint andother loose detrimental foreignmatter by the use of power-assistedhand tools. Power tool cleaning

will not remove adherent mill

scale, rust and paint. Mill scale, rustand paint are considered adherentif they cannot be removed bylifting with a dull putty knife.Power tool cleaning usuallyprovides a slightly higher degree ofcleanliness than hand tool cleaning,but is not regarded as adequatesurface preparation for long-termexterior exposure of most high-performance coating systems.

SSPC-SP5/NACE 1 WHITE METALBLAST CLEANING

The complete removal of all visibleoil, grease, dirt, dust, mill scale, rust,paint, oxides, corrosion products andother foreign matter by compressedair nozzle blasting, centrifugal

wheels or other specified method.

SSPC-SP6/NACE 3 COMMERCIALBLAST CLEANING

The removal of all visible oil,grease, dirt, dust, mill scale, rust,paint oxides, corrosion productsand other foreign matter by

compressed air nozzle blasting,centrifugal wheels or otherspecified method. Discolorationcaused by certain stains shall belimited to no more that 33 percentof each unit area. Unit area isapproximately 9 sq. in. (5776 sq. mm).

SSPC-SP7/NACE 4 COMMERCIALBLAST CLEANING

A brush-off, blast-cleaned surface, when viewed without magnification,

shall be free of all visible oil, grease,dirt, dust, loose mill scale, loose rustand loose coating. Tightly adherentmill scale, rust and coating mayremain on the surface. Mill scale,rust and coating are consideredtightly adherent if they cannot beremoved by lifting with a dull puttyknife. The entire surface shall besubjected to the abrasive blast.The remaining mill scale, rust orcoating shall be tight. When coatingis specified, the surface shall beroughened to a degree suitable forthe specified coating system. Prior tocoating application, the surface shallcomply with the degree of cleaningas specified herein. Visual standardsof comparators may be specified tosupplement the written definition.In any dispute, the written standardsshall take precedence over visual

standards and comparators.

SSPC-SP8 PICKLING

The complete removal of all rust,mill scale and foreign matter bychemical reaction or electrolysisin acid solutions. The degree ofcleanliness is similar to SSPC-SP5/NACE 1 White Metal BlastCleaning.

SSPC-SP10/NACE 2 NEAR-WHITEMETAL BLAST CLEANING

The removal of all visible oil,

grease, dirt, dust, mill scale, rust,paint, oxides, corrosion productsand other foreign matter bycompressed air nozzle blasting,centrifugal wheels or other specifiedmethod. Discoloration caused bycertain stains shall be limited to nomore than 5 percent of each unitarea. Unit area is approximately9 sq. in. (5776 sq. mm).

SSPC-SP11 POWER TOOL CLEANING TO BARE METAL

The removal of all visible oil,grease, dirt, mill scale, rust, paint,oxide, corrosion products, and otherforeign matter. Slight residues ofrust and paint may be left in thelower portion of pits if the originalsurface is pitted. Differs from SSPC-SP3 in that it requires more thoroughcleaning and a surface profilenot less than 1 mil (25 microns).

Although not equivalent, this methodis used for areas where abrasiveblasting is prohibited or not feasible.

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SSPC-SP12/NACE 5 SURFACEPREPARATION BY WATER JETTING

Surface preparation and cleaningof steel and other hard materialsby high- and ultra-high pressure

water jetting to achieve variousdegrees of surface cleanlinessprior to recoating. This standardis limited in scope to the use of

water only without the addition ofsolid particles in the stream. Referto the full standard for all detailsregarding this preparation method.

DEGREE OF CLEANLINESS VS . COAT INGPERFORMANCE

Abrasive blast cleaning as definedin SSPC specifications in SSPCspecifications SSPC-SP5/NACE 1, SSPC-SP6/NACE 3 and SSPC-SP10/NACE 2 is often regarded as

the preferred method of surfacepreparation for carbon steel.Experience has proven that a givencoating system, applied over aproperly blast-cleaned or pickledsurface, will cost less per squarefoot per yard than the same systemapplied over hand or power toolcleaned surfaces. Table II showscomparative cost in relationship tocoating performance. These figuresare based on the typical service lifeof a two-coat alkyd system appliedto ground level, new structural

steel in a mild (rural) atmosphericenvironment. Paint material costsare not included in the figures.

TA BLE I ICOSTS VS . COAT ING PERFORMANCE 2-CoatSurface Years of Preparation Application Total $/Sq. Ft.Preparation Service $/Sq. Ft. $/Sq. Ft. $/Sq. Ft. Per Year

SSPC-SP6 10.5 1.35 0.65 2.00 0.19CommercialBlast

SSPC-SP3 6.0 0.85 0.65 1.50 0.25Power ToolCleaning

The costs referenced in Table IIare approximate, based on 2005data from painting contractorsrepresenting four regions ofthe country.

METHOD OF ABRAS IVE BLAST CLEANING

The SSPC Specification for abrasiveblast cleaning lists a number ofalternative blast cleaning methods.The two most widely used arecompressed air nozzle blast cleaningand centrifugal wheel blast cleaning.Since either method is capable ofproducing the same quality ofsurface preparation, both are equallyacceptable for coating applications. Anincreasing quantity of shop-fabricatedstructural, plate and miscellaneoussteel is now prepared by centrifugal

wheel blast cleaning equipment

because of speed, production capacityand cost advantage of this method. Also, portable centrifugal wheel blastcleaning units can be transported tothe jobsite and set up to processfabricated structural steel and plateassemblies as they are scheduledfor erection.

Vacuum blasting is used in areas where the amount of abrasive dustcreated by compressed air nozzleblasting cannot be tolerated.However, it is recommended thatmotors, bearings and moving parts

close to the work be protected by wrapping with tape.

Other methods of abrasive blastcleaning are not discussed herebecause of their more limited orspecialized applications. Eachhas its own advantages andlimitations which would merit itsconsideration for certain specializedtypes of work.

DETERMIN ING SURFACE CLEANLINESS

The cleanliness of abrasive blast-cleaned steel can be determined bycomparison with SSPC-Vis-1 pictorialstandards. To avoid interpretationsresulting from color and profile

variations due to different typesof steel and abrasive media, small

steel panels can be abrasive blast-cleaned and used as representativesamples of the work. These panelsshould be securely wrapped inclear plastic to protect them fromdeterioration.

MEASUR ING SURFACE PROFILE

It is generally agreed that thesurface profile contributes to theadhesion and performance of mostzinc-rich coatings, tank linings andother high performance systems.Surface profile can be closelypredetermined by the selectionof the type and size of abrasivefrom the tables contained in SSPCand NACE Surface PreparationSpecifications or from the abrasivesupplier’s data.

A number of devices are

available for measuring surfaceprofile. However, it should benoted that different types of testequipment will not necessarilygive comparable readings andcannot be used for comparativepurposes. Therefore, it is necessaryto determine what test equipmentis to be used if duplicate readings

will be taken for verification orapproval. Two methods that seemto be reliable and consistent arethe Keane-Tator Surface ProfileComparator and Testex “Press-O-

Film (Reference NACE RP0287).”In the first method, examinationis made using a 5X lens and apenlight, which is held at an angleto highlight the surface profile. Itis usually sufficient to determinethat the height of the profile liesbetween two gauge readings,such as “between 1S70 and 2S70”(approximately 1.0 - 2.0 mils). Thelatter utilizes a tape that is rubbedon the surface to form an exactreverse image of the profile. Thereplica is then measured with

a micrometer.



SELECT ION OF ABRAS IVE MED IA

Where a sharp angular profileis desired, a sharp, hard abrasivemust be used such as silicasand, or a synthetic abrasive ofequivalent hardness. Coppersmelter slag or soda-lime-silicaglass is recommended when a

nearly dust-free environment isdesired. A recyclable mix that isoften accepted consists of notmore than three parts chillediron shot and one part of chillediron grit. Recycled cast iron andmalleable iron shot and grit, or 100percent chilled shot are regardedas unsatisfactory for producing asharp angular profile, but may beused where this type of profile isnot required.

REMOVAL OF DUST FROM ABRAS IVEBLAST -CLEANED SURFACES

Dust and blast products should beremoved from the surface of abrasiveblasted steel by high-pressure air,

vacuum cleaning or brushing.

CONTAMINAT ION OF ABRAS IVEBLAST -CLEANED SURFACES

The greatest danger ofcontamination during abrasiveblast cleaning is from oil andmoisture. Compressed air used

for nozzle blasting should beperiodically checked to verify thatit is clean, dry and oil-free(Reference ASTM D 4285). Oil and

water separators, traps or otherequipment may be necessary toachieve clean, dry air.

Fabricated steel is sometimes notsolvent-cleaned prior to abrasiveblast cleaning on the assumptionthat oil and grease will be removedby the blast cleaning process.Experience has shown that this is

not always the case. Also, if properquality control procedures are notemployed during centrifugal wheelblast cleaning, the recycled abrasivemay pick up oil, so that in time theabrasive itself will contaminate thesteel being cleaned.

Oil contamination of a blast-cleaned surface is very difficultto detect visually or by ultra-

violet light examination. The bestprotection against oil contaminationis taking remedial measures to

prevent its occurrence. If theblast-cleaned surface becomescontaminated by oil, grease, handprints or other foreign matter, itshould be solvent-cleaned and thenreblasted according to the originalspecifications to ensure the samedegree of surface cleanliness.

ENV IRONMENTAL COND IT IONS

Abrasive blast-cleaned surfacesshould be coated before any visiblerust forms on the surface. For thisreason, it is recommended thatabrasive blast cleaning beperformed only when the relativehumidity is no higher than 85%and the surface temperature of thesteel at its coldest point is at least5° F. above the temperature of thedew point. Some specifiers may

include a time/humidity table intheir specifications to ensure thatthe abrasive blast-cleaned surface iscoated before flash rusting occurs.The general practice is that nomore surface be prepared forpainting than can be coated in asingle shift.

PREPARAT ION OF WELDS

Preparation of welds shouldbe scheduled ahead of surfacepreparation. This work can be

best handled by the metal tradesconnected with fabrication orerection, especially when codeinspection and certification areinvolved. Weld spatter and slagcan be removed by chipping orgrinding. If the surface will beexposed to severe environmentalconditions, it is suggested that sharpedges and corners be roundedto a smooth contour by grinding.Undercuts and recesses should besmoothed by grinding and porous

welds ground down to pinhole-

free metal. Remove weld flux fromthe surface by washing with water(Reference NACE RP0178).

STEEL AND FABR ICAT ION DEFECTS

Steel and fabrication defectsrevealed by surface preparation suchas weld imperfections, delaminations,scabs and slivers should be correctedbefore proceeding further withsurface preparations.

INACCESS IBLE AREAS

It is not possible to properlyprepare and apply a protectivecoating behind rafters or skip-

welded lap joints, or in betweenback-to-back angle iron bracing.These inaccessible areas should becoated before assembly or they will

continue to erode away in acorrosive environment, leaving ruststains on the exposed coated surfacebelow. In an aggressively corrosiveenvironment, coated surfacesadjacent to these areas will actuallybe undercut and fail due to thecorrosive action taking place inthese inaccessible areas. Therefore,if total protection of the surface ismandatory, all surface voids shouldbe seal-welded and back-to-backbracing and tank rafters eithercoated before assembly or

eliminated from the design andconstruction. Sharp corners andedges should be ground to a smoothcontour and welds prepared assuggested in NACE RP0178. (See

Weld Preparation.)

SURFACE PREPARATION OF

DUCTILE AND CAST IRON

The overall performance ofcoating systems is directly relatedto the adhesion developed by the

prime coat to the substrate. Mostcoatings do not achieve optimumadhesion when applied to hard,slick substrates. Adhesion, therefore,is largely dependent on a methodof surface preparation that producesboth surface cleanliness and surfaceprofile (surface roughness).

The Society for Protective Coatings(SSPC) and NACE Internationalabrasive blast cleaning surfacepreparation specifications (SP5/NACE 1, SP6/NACE 3, etc.)

were developed for carbon steel

substrates. Based on informationprovided by the Ductile Iron PipeResearch Association (DIPRA) andTnemec laboratory testing, it hasbeen learned that the manufacturingand processing differences betweencarbon steel and cast iron precludeusing SSPC and NACE surfacepreparation specifications for steel

when preparing cast iron. Indeed,it is possible to “overblast” certaintypes of cast iron (ductile iron,

white iron, gray iron, etc.) which

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could result in reduced long-termsystem performance.

Depending on the process used tomanufacture cast iron, anchor profileafter casting is often higher than

what would be achieved by abrasiveblast cleaning carbon steel. Abrasiveblast cleaning is, therefore, not

always necessary to achieveoptimum adhesion to cast ironsubstrates. Better, more efficientsurface preparation methods canoften be recommended.

The National Association of PipeFabricators has published surfacepreparation standards for ductile ironpipe and cast ductile iron fittings.These standards (NAPF 500-03) canbe referenced along with TnemecTechnical Bulletin No. 98-15.

SURFACE PREPARATIONOF STAINLESS STEEL

In benign environments, stainlesssteel may require only solventcleaning prior to coating, usingany one of the methods in SSPC-SP1. Only solvents and cleaningsolutions containing less than200 ppm of hologens should beused to prevent stress corrosioncracking. Under severe conditionssuch as exterior exposure, chemicalenvironments, etc., the substrateshould be abrasive blasted toincrease mechanical adhesion ofthe coating system. The heightof the profile and the texturerequired should be defined for theoperator and as a standard for theacceptance of the work.

Pictorial standards for the surfacecleanliness of carbon steel are notapplicable to stainless steel sincethere are no corrosion products ormill scale to remove from the surface.Only very hard abrasive media shouldbe used for a fast cutting action andto obtain a sharp angular profile.

SURFACE PREPARATION OF

GALVANIZED STEEL AND

OTHER NON-FERROUS METALS

Surfaces should be clean and dry.Remove dust and dirt by blowingoff the surface with high pressureair or wiping clean with dry rags.Oil, grease, protective mill coatings,and other soluble contaminantsshould be removed by solvent

cleaning in accordance with SSPC-SP1. White rust should be removedfrom galvanized steel by hand orpower brushing. Care should betaken not to damage or remove thegalvanizing. Rust should be removedfrom old galvanized steel by handor power tool cleaning in accordance

with SSPC-SP2 or SP3.

Under moderate to severe conditionssuch as exterior exposure, chemicalenvironments, etc., abrasive blastcleaning or chemical treatment toincrease mechanical adhesion are oftenthe preferred methods of surfacepreparation (Reference ASTM D 6386).

For specific recommendations,contact your Tnemec representativeor Tnemec Technical Services at1-800-TNEMEC1 (ReferenceTechnical Bulletin No. 98-09).

SURFACE PREPARATION OFCONCRETE AND MASONRY

The type of surface preparationrequired for concrete and masonryis dependent upon the type ofcoating system to be applied andthe intended service of the vesselor structure. NACE International,the Society for Protective Coatings,the International Concrete RepairInstitute and the American Societyfor Testing and Materials allreference various methods of

surface preparation. Following aresurface preparation suggestionsand brief descriptions of some ofthe practices recommended byNACE, SSPC, ICRI and ASTM.

SSPC-SP13/NACE 6 SurfacePreparation of Concrete: Thisstandard gives requirements forsurface preparation of concrete bymechanical, chemical, or thermalmethods prior to the application ofprotective coating and lining systems.

ICRI Guideline No. 03732: This

guide provides designers, specifiers,contractors and manufacturers with thetools to select and specify the methodsfor preparing concrete surfaces priorto the application of sealers, coatingsand polymer overlay systems.

T E ST I NG FO R MO IS TURE CO NTENT

New concrete and masonryshould not be coated for at least28 days to permit the concreteor mortar to cure and dry out

unless otherwise directed by themanufacturer. Free water andsoluble alkaline salts remainingin the concrete may contaminatecoatings or eventually causedelamination, blistering, peelingand/or efflorescence staining. Forthis reason, concrete should be

visually inspected and tested formoisture content before painting.

Damp spots, efflorescence or white salts appearing on the

surface are obvious indicators ofmoisture. Hidden dampness can bechecked by using a polyethylenecover test. A heavy gauge plasticfilm, approximately 18 in. squareand 4.0 mils thick, is securelytaped to a small section of theconcrete. Pieces of test film shouldbe placed at various locationsthat are likely to be slow drying,such as below grade, low spots infloors, inside corners and lower

wall areas. The polyethylene sheetis checked after 24 hours for

beads of moisture. If condensationappears on the back side of thefilm, or if the concrete underthe film appears to be darker,damp or wet, this would indicatethe presence of moisture in theconcrete. Reference ASTM D 4263for the complete procedure priorto proceeding. Should moisture bedetected, perform “Standard TestMethod for Measuring Moisture

Vapor Emission Rate of ConcreteSubfloor Using Anhydrous CalciumChloride (Reference ASTM F 1869).”

Moisture content is not to exceedthree pounds per 1,000 sq.ft. in a24-hour period.

REPA IR OF SURFACE DEFECTS ANDREMOVAL OF CONTAMINANTS

The surface to be coated shouldbe examined for defects such asfins, protrusions, bulges and mortarspatter. These defects should becorrected by grinding or scraping.Repair of surface defects includes

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Tape

Heavy GaugePlastic Fi lm



patching voids and cracks that willcause discontinuities or unsightlyappearance in the coating, andusing a patching compound that iscompatible with the coating system.Remove non-degraded release agents,fats, oil, wax and grease by scrapingoff heavy deposits followed bycleaning with an appropriate solventor washing with a hot trisodiumphosphate solution, using 2 lbs. oftrisodium phosphate to each gallonof hot water (160° F.). Repeat thecleaning operation until thecontamination is removed and flushthe area with clean water to removeresidual cleaning solution. If TSPcleaning solution does not provideadequate results, consult a reputablesupplier of chemical cleaners toprovide assistance in choosing anadequate alternative. Always ensure

that the cleaning solution ismaintained at a constant temperaturelevel to keep the contaminantssoluble until they are removed. Allowto dry thoroughly before coating.

REMOVAL OF WEAK LA ITANCE

High-build, high film strengthcoatings will not develop optimumadhesion to concrete unless laitanceand other loosely bound materialare first removed from the surface.Common methods of removal are

acid etching and abrasive blasting. Abrasive blasting is preferred wherepractical, although dust and abrasiveremoval may present a problem onsome projects. Acid etching is aneconomical way to prepare concretefloors. However, is hazardous in itsapplication and is not recommendedfor vertical or overhead surfaces.

ABRAS IVE BLAST ING

Abrasive blasting should besufficiently performed so as to

remove weak laitance and solidcontaminants. This procedure willopen up surface voids, bugholes, airpockets, etc. Concrete substrates areabrasive blasted to provide a clean,sound substrate with a uniformanchor profile, but not to erodethe surface beyond that which isnecessary. Recommended blastingmethods include dry abrasive withair-blast, hydroblasting with anabrasive and airless centrifugal

wheel blast, and vacuum blasting.

Abrasive blasting using compressedair is the more common method ofabrasive blasting. The blasting is oftenperformed dry, but can incorporate

water to control dusts. The watercan be mixed with the abrasive andused as a slurry or the water canbe injected into the abrasive at theend of the blast nozzle. Before wetblasting, one should consider theschedule constraints of the project.Time may not allow for ample dryingof the surfaces before coatings areto be applied. The selected abrasivemust be clean and dry with amaximum particle size that can passthrough a 16-mesh screen.

The preferred method of abrasiveblasting floors is with a portableunit incorporating centrifugal wheelblast using steel shot abrasive.These units reclaim much of

the shot and subsequent dusts,minimizing the final clean-upbefore coating. The size of thesteel shot, coupled with the travelspeed of the unit, determines theaggressiveness of the blast cleaning.

After blast cleaning, residualabrasive, dust and other looseparticles must be removed from thesurface by vacuuming or blowingoff with clean, dry compressedhigh-pressure air. Reference ASTMD 4529, SSPC-SP13 and ICRI Guide03732 for the complete proceduresand guidance regarding abrasiveblast cleaning.

ACID E TCH ING

Acid etching is often used onhorizontal surfaces because itprovides results at a low cost. It isimpractical and dangerous to use for

vertical and overhead surfaces as it

will not etch the surface uniformlyand does not have any effect onopening voids and holes near thesurface. Typical solutions used aremuriatic (hydrochloric), phosphoric,and citric acids.

Because it’s volatile, hydrochloricacid should not be used around

sensitive mechanical or electricalequipment. Citric acid is often used ifthe acid solution will be rinsed downstainless steel pipes.

Acid etching may not be suitablein some situations where theconcrete surface has been powertroweled and/or a thick filmcoating system has been specified.For specific recommendations,contact your Tnemec representativeor Tnemec Technical Services.

Residual dust and dirt should be

removed from the surface of theconcrete by thoroughly sweepingor vacuuming.

Apply fresh water to dampen theconcrete surface, but do notexcessively wet. Remove any excess

water with brooms or rubbersqueegees. The acid solution shouldbe applied uniformly to the concreteby low pressure spray equipment orplastic sprinkling cans.

The spreading operation shouldbe coordinated with the rinsing

operation so that the acid is notcompletely spent or has startedto dry out before the surface isflushed with fresh water. Bubblingshould be uniformly evident andthe acid wetted area should bescrubbed with a stiff bristle brush.

Etched concrete should be examinedfor uniformity and texture, and shouldhave the feel of medium (100 grit)sandpaper or compare to ICRI CSP1.The surface should be free of surfaceglaze, laitance, salts and looselyadhering material. In many cases,

more than one acid etching operationis required to obtain a satisfactoryprofile. Reference ASTM D 4260, 4262,4263, SSPC-SP13 or ICRI GuidelineNo. 0373 for complete proceduresbefore proceeding.

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Acid Etching



SURFACE PROFILE GU IDEL INES

Achieving sufficient profile isextremely important to floor toppingadhesion. It is recommended thatprofile should be increased withincreasing topping thickness. Surfaceprofile guidelines are referenced inthe table below for resinous (organic)

flooring system.

TA BLE I I ISURFACE PROFILE GU IDEL INES :RES INOUS FLOOR ING SYSTEMS

F loo r Topp ing/ I CR I Conc r e teOve r lay Th i c knes s Su r fac e P ro f i l e No .

0 - 3 m i l s C SP1 -3

4 - 10 m i l s CSP1 -3

10 - 40 m i l s CSP3 -5

50 m i l s CSP4 -6

1/8" - 1/4" CSP5 -9

* When inorganic or cementitious floor toppingor overlays are used, additional substrateprofile is recommended along with otherspecial considerations not covered herein.

Note: If rebar is exposed by degradation orpreparation, removal of concrete around entirecircumference of rebars is recommended.

SURFACE PREPARATION

OF PLASTER

Plaster should be permitted tocure and dry out for at least 28

days before painting. Coating overplaster that contains free water,lime and other soluble alkalinesalts may cause delamination,blistering, peeling, discoloration,efflorescence or staining. If thereis a question about the moisturecontent of the plaster, it should bechecked and verified followingthe procedure outlined forconcrete. Give attention to areasthat are likely to slow the dryingout process.

Remove plaster nibs and otherprotrusions by scraping. Greaseand oil may be removed by ahot cleaning solution consistingof 2 lbs. of trisodium phosphateto each gallon of hot water. Thecleaning solution may be appliedby sponge or brush, working fromthe bottom to the top of the soiledarea. The cleaning operation shouldbe repeated if the contaminants are

not completely removed. Flush thecleaned surface with fresh waterand allow drying. Patch voids andcracks with a suitable compoundthat is compatible with the substrateand coating. Sand flush with thesurface when cured or dry.

SURFACE PREPARATIONOF GYPSUM DRYWALL

CONSTRUCTION

Sand joint compound with finegrit, open-coated sandpaper toprovide a smooth flat surface.

Avoid heavy sanding of the adjacent wallboard surfaces, which will raisethe nap of the paper covering.Remove dust from the surface by

wiping with clean rags or othermeans. If additional joint finishingis required to provide a smooth

surface, the same joint compound ora ready-mixed spackling compoundshould be used. Putty, patchingpencils, caulking or masking tapeshould not be applied to drywallsurfaces to be painted.

Lightly scuff-sand tape joints afterpriming to remove raised papernap. Take care not to sand throughthe prime coat. Remove dust by

wiping with clean rags.

SURFACE PREPARATION

OF WOOD

Wood should be clean and dry.Remove surface deposits, sap or pitchby scraping and wiping clean withrags dampened with mineral spiritsor VM&P Naphta. Seal knots andpitch pockets with shellac reduced

with equal parts of shellac thinner(denatured alcohol) before priming.Sand rough spots with the grain,starting with medium grit sandpaperand finishing with fine grit. Removesanding dust. After the prime coatis dry, fill cracks and holes with asuitable compound that is compatible

with the substrate and coating. Whenfiller is hard, sand flush with thesurface using the fine grit sand paper.Sand lightly between coats with finegrit, open-coat sandpaper.

SURFACE PREPARATION

OF PREVIOUSLY PAINTED

SURFACES

Whether or not overcoating isa feasible alternative to completeremoval and repainting depends agreat deal on the condition of the

existing coating system. The amountof corrosion present, number ofcoats, adhesion between coats andexposure conditions are some of thefactors that need to be consideredbefore a specifier can make anovercoat or complete removaldecision. Tnemec Technical BulletinNo. 98-10 R1 can be used as aguide to assist in making completeremoval versus overcoat decisions.

Surface preparation of an existingcoating system will vary dependingon generic type, exposure conditions

and other variables. For specificrecommendations, contact yourTnemec representative or TnemecTechnical Services.

9

Various surface cleaning methods are used withpower tools to remove loose rust, loose paintand loose mill scale. Pictured above top, aheavy-duty roto peen flap wheel, and bottom, apower tool with a non-abrasive cup wheel.



10

While surface preparation is usuallydefined and controlled by thespecification, application is frequentlyspecified to be performed “inaccordance with the manufacturer’s

direction.” These directions usuallyinclude ranges or limits governingthe use of the product such as airand surface temperature, recoat time,spreading rate, film thickness, etc.They also include recommendationsfor various methods of applicationsuch as brush, roller, or spray, as wellas mixing and thinning instructions.For most types of coatings, themanufacturer’s recommendationscontain more than one method ofapplication and the applicator hasthe option of choosing the method of

application that is most economicalor best suited for a particular job.

The term “application” is nolonger limited to just applicationmethods, but has been expandedto include a number of relatedfactors such as environmentalconditions, material preparation,equipment, film characteristics,curing and recoating. Each of thesefactors has a bearing on the properapplication of the coating system.

STORAGE AND HANDLING

Facilities should be available atthe shop or jobsite for handlingand storage of coatings inaccordance with the manufacturer’srecommendations. In mostinstances, coatings should bestored in a protected or enclosedarea where temperature conditionsare controlled. Excessively highor low temperatures may affectapplication properties of a coatingsufficiently so that it cannot

be properly applied until it isbrought within the recommendedstorage temperature range again.Furthermore, the physical andchemical properties of coatingsmay be adversely affected bystorage at temperature extremes.

All materials should be stored insealed containers prior to use. Anymaterial held in storage beyondthe manufacturer’s shelf life limitsshould be withdrawn from stock

and disposed of in accordance withthe appropriate regulations.

T EMPERAT URE AN D HUMI DI TY

Manufacturer’s data on air andsurface temperature limits andrelative humidity should be adheredto during the application andcuring of coatings. While somecoatings will tolerate much broadertemperature and humidity rangesthan others, the application andperformance of any coating canbe adversely affected if prescribedlimits are not followed. (See FilmCharacteristics Section.) Eventemperature variations within theselimits may change the applicationproperties of some coatings,requiring solvent and equipmentadjustments as recommended by themanufacturer for proper application.

Continuous recording pyrometersand hygrometers are often employedto monitor temperature and humidityconditions during the applicationand curing of coatings wherethese factors are essential to filmformation and cure. If this type ofequipment is not available, periodicreadings can be taken with air and

surface temperature thermometersand a sling psychrometer, and thenrecorded to verify temperature andhumidity conditions which weremaintained during the coating andcuring phase.

This is not to imply that allcoatings applications must bemonitored in this manner.However, it may be helpful tohave such instrumentationavailable to settle questions

where there is doubt as to whether the temperature andhumidity conditions are suitablefor the application of a coating.

WIND VELOCITY

Excessive wind velocity canseriously impair spray application,resulting in significant materialloss, low film build, excessivedry spray or overspray, plus thepossibility of depositing airbornespray mist on unprotected surfaces

downwind from the work. Someof these adverse effects can becompensated for by material andequipment adjustments if winds arenot too high. Generally speaking,

wind velocity above 15 m.p.h. cancause sufficient spray applicationproblems, in which case suspending

work until conditions improveshould be considered.

VENT ILAT ION

Nearly all coatings contain sometype of solvent which mustevaporate from the film as part ofthe drying or curing process. Whiletemperature plays an importantrole in solvent evaporation,

ventilation is even more essentialto the process. Supplementary

ventilation, such as fans and blowers, should be employed in confined orenclosed areas to carry off solventsduring the evaporation stage.

DUST AND CONTAMINAT ION

Airborne dust and contaminantssettling on freshly appliedcoatings not only produce anunsatisfactory “sandy” appearance,but also provide a critical path forpenetration of the film, shorteningthe service life of the coating.Chemical contaminants mayactually attack the film and laythe groundwork for early failureof the coating system. Coating

work should be scheduled toavoid excessive dust and airbornecontaminants, or work areasshould be protected from theseadverse conditions during theapplication and curing phase.Surface accumulation of dustand contaminants on previouslycoated work should be removedbefore applying succeeding coatsto prevent intercoat contaminationand loss of adhesion.

MIX ING AND TH INNING

Most coatings will stay insuspension for several hours aftermixing without further stirring oragitation. However, some are proneto rapid settling and must be stirred

A P P L I C A T I O N G U I D E



11

frequently or kept under constantagitation during application. Themanufacturer’s direction should befollowed in these instances.

Nearly all coating materials aresubject to some degree of settlingor standing in the container, andrequire stirring or mechanical

agitation before application. Someproducts require the addition ofsolvents to adjust the viscosity fordifferent methods of applicationand variations in temperature. Onlythe type of solvent recommendedfor the coating should be usedand the material should not beoverthinned. Do not thin coatingsbefore initial stirring, sincesome materials develop a falsethixotropic body on standing,

which breaks down to normal viscosity with stirring or agitation.

Most coatings will stay insuspension for several hours aftermixing without further stirring oragitation. However, some are proneto rapid settling and must be stirredfrequently or kept under constantagitation during application. Themanufacturer’s direction should befollowed in these instances.

MULT I - COMPONENT

Multi-component productsare either packaged in doublecompartment containers or separatecontainers marked “Part A” and“Part B” or some other designationand contain the precaution not touse without mixing all components.Multi-component materials arepremeasured in the container sothe proper mixing ratio can beachieved by mixing the entirecontents of each container.

The manufacturer’s instructionsusually recommend that the mixingbe done under agitation. With

some materials, it is importantthat the components be addedin a prescribed sequence andthe procedure should not bereversed. Thorough blending ofthe components is essential forproper performance of the coatingand power agitation is generallyrecommended. Thorough blendingof two liquid components can take1-3 minutes with the proper sizemixing blades. If a dry powdercomponent is added to a liquid

component, the two should bethoroughly blended until they arefree of lumps. Usually straining isrecommended before application toremove any undispersed materialthat could clog spray equipment.

It is advisable to have someonefamiliar with the product supervise the

mixing of multi-component materials. A mixing error such as leaving out oneof the components, using the wrongmixing ratio, insufficient mixing oradding the wrong component, willresult in an unsatisfactory product. Thematerial should be discarded, unlessit is definitely known what the error

was and the mix can be correctedto conform with the manufacturer’smixing instructions. If improperlymixed material is applied to thesurface, it is generally necessary tocompletely remove the coating and

recoat the surface with properly mixedmaterial. Consult the manufacturer fortheir recommendation.

POT L IFE

Nearly all mixed multi-componentmaterials have a pot life, or timelimit, during which the mixedmaterial can be used. The potlife will generally vary withtemperature and is usually muchshorter at higher temperatureranges. Pot life limits must be

strictly observed. Care should betaken not to mix more materialthan can be applied during thepot life. If the pot life has beenexceeded, the material should bediscarded even though it may stilllook like it is satisfactory to use.

APPL ICAT ION EQU IPMENT AND TECH NIQ UES

Application equipment andtechniques recommended by thecoating manufacturer are usually

based on test reports from theequipment manufacturers, testapplications and field experiencegained under a variety of jobconditions. The type of equipment,pressure settings and applicationtechniques recommended by themanufacturer will usually permitsatisfactory application of thecoating under most job conditions.

Variations in equipment, pressuresettings and technique can bemade by the applicator as long as

proper atomization and applicationcharacteristics are not affected. Forunusual or specialized applications,it is recommended that the coatingmanufacturer be consulted.

It is important that tools andequipment be clean and in goodoperating condition. Dirty tools

and equipment can be a source ofcoating contamination, and brokenor worn-out equipment may not becapable of satisfactory application.Frequently, the material is blamedfor application problems when thereal problem is the use of wrongor defective equipment.

F ILM TH ICKNESS AND SPREAD ING RATE

Adequate film build is essential tothe satisfactory performance ofprotective coatings. The coating

manufacturer will specify the spreadingrate (sq. ft. per gallon) that is requiredto achieve the specified dry filmthickness. The calculations are basedon the fact that each standard U.S.gallon (128 fluid ounces) contains1,604 mil sq. ft. of liquid. If it isdetermined that a dry film thicknessof 3.0 mils (0.003 inches) is required,and it is known that the productcontains 54 percent solids by volume,the theoretical spreading rate wouldbe calculated at 289 sq. ft. per gallon(1604 ÷ 3 X .54=288.7) and the wet

film thickness would be calculated at5.6 mils (1604 ÷ 288.7=5.55).Calculations are usually rounded offto the closest 5 sq. ft. and closest 0.5mil for convenience. Theoreticalspreading rates do not includematerial losses due to the method ofapplication or surface irregularities.Deductions for material losses shouldbe made to arrive at a practicalspreading rate.

Film thicknesses and theoreticalspreading rate can be quickly

determined from Table IV on thenext page if the solids by volumeare known.

Theoretical spreading ratesmay be used as a rough guidefor determining film thickness.However, in order to assuresufficient material is being applied,

wet film thickness readings areoften taken at random locationsimmediately after application.

A Nordson Wet Film Gauge orsimilar instrument may be used



for this purpose. The dry film canbe calculated by multiplying theaverage wet film thickness by thepercent solids by volume. Forexample, if the wet film averages8.0 mils, and if the solids by

volume are 54 percent, the dryfilm thickness would be calculatedat 4.3 mils (8.0 X 0.54 = 4.3).Consideration should also be givento variables that could have aneffect on the calculated dry filmthickness, such as loss of wet filmdue to absorption into a poroussubstrate, surface profile, thinning, etc.

Dry film thickness may bemeasured on ferrous metals usinga magnetic gauge following theprocedure outlined in SSPC-PA2, Section IV, Paint ThicknessMeasurement. On a non-ferroussurface, dry film thickness readings

can be taken with a Tooke Gaugeor gauges designed for non-ferroussubstrates utilizing eddy currentprinciples. Readings should be atrandom locations at the rate ofapproximately five readings perone hundred sq. ft. of surface.The average of all readings for agiven area or surface should be

within the dry film thickness rangespecified and no individual reading

should be more than 20 percentbelow the recommended dry filmthickness. Any areas that are foundto be below standard should bemarked and recoated to obtain theproper film thickness.

While primary concern should begiven to applying sufficient film

thickness for adequate protection,it is sometimes equally important toguard against applying too heavy acoat. Excessively heavy coats mayresult in runs and sags, producingan unsightly appearance as wellas leaving weak spots in the film.Heavy coats may also upset thedrying properties, causing wrinklingor cracking, affect intercoatadhesion or leave excessivesolvents trapped within the film.

F ILM CHARACTER IST ICS

The object of application is todeposit a coating on the surfacethat will provide the decorativeand protective properties thatare inherent with the coating.This requires that the coating beuniformly applied at the prescribedthickness, and be free of filmdefects that would adversely affectthe appearance or performance.

Due to advancements inapplication technology, betterapplied coatings are easier toachieve than ever before. However,the state-of-the-art has not reachedthe point where shop and fieldapplicators can apply coatingsystems that are completely freeof defects. Furthermore, not allfilm defects will adversely affectperformance and/or appearanceand many types of minor defects

would not be a basis for rejectionof the work or even necessitatetouch-up or repair. Also, thereare differences in the acceptancecriteria for a decorative coating,

where appearance is the primaryfactor, and a protective coating,

where performance is the mostimportant consideration. Therefore,it is important that the inspection

and acceptance criteria be definedin advance for the applicator. If dryfilm thickness measurements areto be taken or Holiday DetectorTests run, it should be established

what type of test equipment is tobe used, where and how manyreadings are to be taken, who willperform the inspection and whatkind of inspection records are tobe kept.

12

Ta b le I V

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

1600 800 600 400 300 200 150 100

MILS DRY FILM

P E R C E N T

S O L I D S B Y V O L U M E

100

90

80

70

60

50

40

30

20

10

0

75

50

25

SQUARE FEET PER GALLON 1 Start by locating thecorrect solids by volume

line on the left-handside of the chart.

2 To determine the milthickness for a givenspreading rate, follow

the solids by volume lineacross to where it inter-sects with the correct

spreading rate diagonalline and read down.

3 To determine thespreading rate at a givenmil thickness, follow the

solids by volume lineacross until it intersects with the correct film

thickness line and locatethe closest spreadingrate diagonal.

4 Extrapolate values

in-between lines.



Defining the acceptance standardsfor the appearance of a coatingis more difficult. Often times, thespecification language emphasizes

what coating characteristics arenot acceptable rather than what isacceptable. For example: “Finishcoats shall be free of runs, sags,skipped and missed areas, etc.”This is often backed up with therequirement that a small area ofa room be coated and approvedbefore proceeding with the rest ofthe job.

This procedure points out theneed for a common languageto describe film characteristicsin order to avoid costlymisunderstandings and delaysin dealing with shop or fieldapplications. Table VI on the nextpage lists a number of common

film characteristics and gives theirprobable causes as well as variousmethods of correction. The term“Film Characteristics” rather than“Defects” was chosen intentionallyand no implication is made thatany of the conditions listed wouldnecessarily constitute defective

work or form a basis for rejection.

HOLIDAY TEST ING

If required by the projectspecifications, holiday testing

should be performed in accordance with NACE RP0188. For coatingthicknesses less than 20.0 mils DFT,use a Tinker & Rasor low voltageModel M/1 Holiday Detector, orequal. For coating thicknessesgreater than 20.0 mils DFT, high

voltage discontinuity (spark)testing shall be performed using aTinker & Rasor AP/W High VoltageHoliday Tester. As a general rule,

voltages are set between 100-125 volts per dry mil of coating.Contact Tnemec Technical Service

for voltage recommendations andcuring parameters prior to testing.

CUR ING AND RECOAT ING

So many of today’s coatingsachieve film formation bysuch complex mechanisms ascoalescence, hydrolysis andchemical conversion, that the term“drying” is hardly appropriateto describe these phenomena.

Gradually, the term is beingreplaced by the word “curing” torefer to the interphase between wetfilm and dry or fully-cured film.Table V lists the four phases ofcuring that are typically referenced.

TA BLE V

1. To Touch—The point at whichthe film will no longer pickup on the finger when lightlytouched.

2. To Handle (or dry-throughtime)—The point at whicha coating will not loosen,

wrinkle, detach or distort whenmaximum downward thumbpressure is exerted and thethumb is turned.

3. To Recoat—The point at whichthe film is sufficiently cured toreceive the next coat withoutadverse effects.

4. Full Cure—The point at whichthe film initially reaches itsfull physical and chemicalproperties and is ready to beplaced in service.

The time it normally takesto reach these various phasesin the curing cycle at ambienttemperature will be provided

by the coating manufacturer. Variations in film thickness,temperature, humidity and airmovement during the curingcycle will affect the actual lengthof time of each of these phases.Therefore, the time factor alonecannot be relied upon completelyfor determining when a coatingis sufficiently cured to handle,to touch, to recoat or when itreaches full cure and is ready toplace in service.

Some coatings, such as coal

tar-epoxies, have a maximumrecoat time and must betopcoated within this time limitfor proper intercoat adhesion andperformance properties. If, forsome reason, the maximum recoattime is exceeded, the manufacturershould be consulted beforeproceeding to prevent possibleproblems or costly failures.

13

Wet Mil Gauge

Type II Dry Film Thickness Gauge



Characteristic/ ProbableDescription Cause Correction

Ta b l e V I

Alligatoring-Cross-hatch pattern ofsurface cracking.

Bubbling-Bubbles on the surfaceof the fried film. May bemicroscopic in size.

1. Incompatibility oftopcoat and underfilm,or coating over a softunderfilm.

1. Remove failed coating andrecoat with compatiblesystem suitable for exposureconditions. Do not topcoat

until underfilm is dryenough to recoat.

1. Level surface defectsby sanding and reapplycoating at lower air orsurface temperature, or addslower solvent to increaseopen time of wet film.

2. Bridge or fill voids byapplying a mist coat, afiller or sealer.

3. Remove bubbles by sandingand reapply coating at alower relative humidity.

Allow coating to cure beforecontacting moisture.

1. Rapid volitization ofsolvents within the film.

2. Air displacement result-ing from absorption ofwet film into poroussubstrate.

3. Urethanes in contactwith moisture.

Flatting-Loss of gloss.

1. Rain, fog, high humidity,or damp surfaces.

2. Overthinning or use ofwrong solvent.

1. Recoat when surface is dryand weather conditions aresatisfactory.

2. Remove coating if filmproperties or adhesion areaffected and recoat withproperly thinned material.

Framing-Color, texture or hidingvariations when roller-applied surfaces join workcut in with a brush.

1. Uneven film build betweenroller- and brush-appliedwork.

1. Recoat deficient work,apply heavier wet filmor an additional coat onnew work.

(Poor) Hiding-Uneven color or shadowyappearance of topcoat.

1. Insufficient number ofcoats or low film build.

1. See “Framing.” (Note: Somecolors have weak hiding proper-ties and require an additionalcoat for satisfactory hiding.)


Cracking-Visible cracks through thesurface of the film.

1. Patch cracks and recoat.

2. Replace with coating havingsufficient flexural strengthto tolerate condition.

3. Replace with coating thatwill tolerate physicalconditions.

4. Recoat when air and surfacetemperatures are aboveminimum recommendations.

1. Stress or compressioncracking of rigid sub-strate.

2. Bending or flexing ofnon-rigid substrates.

3. Physical damage:impact, heat, cold,exposure, etc.

4. Surface freezing of freshlatex coatings.

Cratering-Round V- or U- shaped thinspots or voids.

1. See “Bubbling.”1. Caused when bubblesbreak.

Crazing-Fine line cracking forming anetwork or overall pattern.

See “Cracking.”See “Cracking.”

Delamination-Loss of adhesion tosubstrate or between coats(inter-coat adhesion).

1. Remove coating not tightlybonded, clean surface andrecoat.

2. Correct cause of watermigration, remove coatingnot tightly bonded and

recoat.3. Remove coating not tightly

bonded, abrade surface andrecoat. (See Manufacturer'sinstruction.)

4. Completely remove coatingand recoat with compatiblesystem.

1. Dust, dirt, contamina-tion, dry spray.

2. Water migration throughporous substrates.

3. Underfilm allowed tocure beyond maximumrecoat time.

4. Topcoat incompatiblewith underfilm.

Dry Spray-Rough, sandy surfacetexture on spray-appliedcoating.

1. Sand smooth and adjustmaterial, equipment andtechniques for prevailingtemperature and humidityconditions.

1. Spray particles partiallydry before reachingsurface.

Holidays-

Skipped or missed areas.

1. Touch-up or recoat.

Lapping(Lap Marks)-Color, sheen or texturevariations where one freshlypainted area overlaps another.

1. First area painted hasset up before overlapwas made.

1a. Adjust material, equipmentand technique for weatherconditions.

1b. Work smaller areas to reducelap time.

Overspray-Rough sandy areas onspray-applied work.

1. Deflected spray mist thatsettles on dry or partiallydry coated surfaces.

1. Sand smooth and recoat usingproper application techniqueand lap time. Protect dry filmfrom overspray.

Mud Cracking-Cross-hatched pattern ofsurface cracking.

1. Excessive film build orhot, dry weather.

1. Remove failed coating andrecoat at recommended filmthickness. Add additionalsolvent or slower solvent toretard drying during hot, dryweather.

Orange Peel-

Fine pebbled surface textureon spray-applied coating.

1. Insufficient atomization.

Pinholing-Small holes ordiscontinuities in the film.May be microscopic.

1. Sand smooth and recoat after

adjusting material, equipmentand technique to obtain betterflow and leveling.

Peeling-See “Delamination.”

1. Solvent migrationthrough the film after thefilm has begun to set.(Also see “Bubbling”

and “Cratering”.)

1a. If occasional pin holes aredetected, touch-up or recoat.

1b. If pinholing is a general

surface condition, it indicatesthat coating was appliedand cured under adverseenvironmental conditions.Apply a thin or mist coat tofill surface voids, followedby a full wet coat whenenvironmental conditionsare suitable for recoating.

14



15


Ta b le V I

Roller Tracks-(a.) V-shaped texturepattern on roller-appliedsurfaces (chicken tracks)

or (b.) Lines at edge ofroller passes.

1. Use of long nap rollercover on smoothsurfaces.

2. Material not properlythinned.

3. Material not rolled outproperly.

1. Change to shorter naproller cover.

2. Make solvent adjustmentto improve flow andleveling.

3. Use proper applicatortechnique.

Runs-Heavy V-shaped or pencilshaped vertical build-upson surface of coating.

1. Excessive film build.

Streaking-Areas having a rough tex-ture on spray surface.

1. Equipment malfunctionor use of wrongequipment.

2. Spray passes not prop-erly lapped.

1. Sand smooth and recoatafter correcting equipmentmalfunction or change torecommended equipmentif wrong equipment wasbeing used.

2. Sand smooth and recoatusing proper applicatortechnique.

Water Spotting-

See “Flatting.”

Wrinkling-Formation of wrinklepattern on top of film.


2. Slow drying conditions.

1. Sand smooth and recoatat proper film thickness.

2. Sand smooth and recoatwhen drying conditionsare satisfactory.

ACKNOWLEDGMENTS

Tnemec is indebted to the members and technical

committees of the various professional and technicalorganizations listed below. Their contribution tothe advancement of the coating industry has made itpossible for us to assemble the information containedin this guide:

• American National Standards Institute

• American Society of Testing and Materials

• American Water Works Association

• Construction Specification Institute

• International Concrete Repair Institute

• NACE International• Society for Protective Coatings

• Technical Association of Pulp and Paper Industry

• Water and Waste Equipment Manufacturers Association, Inc.

• Water Environmental Federation

Tnemec believes in working hand-in-hand withprofessionals in these various fields and maintainsactive membership and technical representation inall of the above organizations.

Sandy(Appearance)-Dull, rough appearanceof film.

1. Dust and dirt contami-nation of the wet film.

1. Sand smooth and recoat.Protect freshly paintedareas against dust and dirtcontamination or suspendpainting operations untilenvironmental conditionsare satisfactory.

Shadowing-See “Hiding.”

1. See “Hiding.” 1. See “Hiding.”

Solvent Trap-Residual solventsremaining within film.


2. Low temperature curing.

1. Try to drive solvents outof film by force-drying,(see manufacturer’s data),test for hardness andadhesion. If film will not

adhere or cure properly,remove and recoat.

2. Same as “1.”

Sags-Heavy U-shaped build-upsor horizontal lips on thesurface of coatings. (Longsags may also be referredto as curtains.)

1. See “Runs.” 1. See “Runs.”



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Documents

Surface Prep App Guide