overcoating: maintenance or mayhem?017-26)f...“power tool cleaning.” surface tempera-ture should...

alert the owner that maintenance paint-ing will be needed, and planning andpreparing work orders or contractsshould be initiated. The impact on oper-ations, safety and access are evaluatedto determine the possible implicationsthat may be imposed by maintenancepainting activities, including shutdowntimes, lane restrictions on bridges andcontractor access.

Coating ConditionAssessmentA coating condition assessment may belimited to a visual assessment or involvea closer inspection of the coating sys-tem. The physical and chemical charac-teristics of the existing coating system,including adhesion, coating layers andthickness, degree of rusting or corrosion,topcoat resin type and the presence ofheavy metals (e.g., lead or chromium)may all be measured or evaluated whenextensive assessments are conducted.Refer to to SSPC “Technology UpdateNo. 3, Overcoating” (SSPC-TU 3) for dis-cussion on the use and possible interpre-tation of such collected data. When over-coating appears to be a viable option for

hether a bridge, tank,pipeline, vessel, manu-facturing facility, archi-tectural structure or

amusement park ride, at some pointthere will be a need for maintenancepainting. The “paint guy” will shareresponsibility with those involved in gen-eral maintenance, funding, prioritizing,public relations and safety.

Those familiar with maintenancepainting may recall the four mainte-nance painting strategies:Do nothing: The structure, including thecoating system, is in good or very goodcondition. Maintenance painting is simplynot necessary or needed. A second “donothing” option involves the “extremecondition,” when the coating and corro-sion breakdown of the structure or itemis so poor that it will be demolished,retired or decommissioned.Spot repair: Cleaning and coating only afew areas or sections of a structure willenhance corrosion protection, is relative-ly inexpensive and the aesthetics are nota major consideration. Localized areasare cleaned and spot rust and degradedor poorly adhered coatings are removed.One or more protective coating layersare applied to the area.Spot repair and overcoat: Coatingdeterioration and breakdown in one ormore of the existing coats is providingsome protection from corrosion, but ero-sion, weathering or other environmentalconditions have compromised the barrierprotection and/or detracted from thedesired aesthetic condition. Overcoatingmay be applied to the entire surface orbe limited to specific areas such asthose visible to the public. Remove and replace: This mainte-nance option is employed when existingcoating systems need to be entirelyremoved and replaced due to extensivebreakdown and corrosion of the struc-

By Richard A. Burgess, KTA-Tator, Inc., Series Editor

paintsquare.com / JPCL February 2015 17

Cases fromthe F-Files

ture or item. Depending on the serviceenvironment and other considerations,this approach may apply to all or onlysections (zones) of the surface area.

This column focuses on overcoating,which nearly always includes somedegree of spot repair and touch-up appli-cation. Whether to enhance corrosion pro-tection, restore and improve aesthetics orboth, pre-planning and providing effective,straight-forward specifications are criticalto success. Considerations appropriatefor overcoating, or any other scope ofmaintenance painting for that matter, arebriefly described simply to provide somecontext for determining if overcoating is areasonable maintenance option.Recommendations for project specifica-tions follow these considerations.

Pre-PlanningMaintenance painting is most frequentlytriggered by some visual condition, beit corrosion and rusting, loss of glossor color and at times for regulatory pur-poses (safety color codes). This mayresult in execution of a maintenanceplan or program that already exists (forexample, in petrochemical facilities), or

Overcoating: Maintenance or Mayhem?Best Practices for Writing an Overcoating Specification

Mechanisms of Failure

W

Fig. 1: Coating compatibility is a bigger problem for overcoating than many believe. All photos courtesyof the author.

18 JPCL February 2015 / paintsquare.com

can be used to establish the details forcontracts, work orders, special provi-sions and specifications.

Any additional aspects of the overallscope of the project should be detailed.This may include repair or replacementof steel elements or components, identifi-cation where specific procedures may berequired (coating tie-ins), remediation ofsoluble salts, specific cleaning agents orprocesses to neutralize or sequester sur-face contaminants, and limitations on thesurface preparation and/or applicationprocedures permitted.

When abrasives are used, restric-tions, such as the use of silica sand,should also be considered. Safety,health and environmental issues arealso part of the project planning. Leadpaint is lead paint, whether it is on aprocess vessel, bridge or water tank.

F-Files: Mechanisms of Failure

maintenance painting, the use of testpatches to evaluate surface preparationand candidate coatings should be consid-ered early in the project planning phase.

Project PlanningThe scope of the maintenance paintingto be performed may be established

based on historical experience, the coat-ing condition assessment (general ordetailed), available funding or test patchand other testing results. However, oncethe scope has been established, thedetails of the project and its impact onoperations, the public, budget, duration,season, timing and details for execution

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Fig. 2: Edge coating should include a stripe coat,even for spot repairs.

Fig. 3: Overcoating does not need to be a “one-and-done” strategy.


Compliance with all regulatory require-ments must be included in planning, aswell.

Seemingly mundane details canescape consideration if not included inthe detailed plan, such as who will supplypower, compressed air, water, scaffold-ing and controls access (contractor orowner).

Contract Documents andWork OrdersPreparation of the contract or work orderdocuments should include general andspecific conditions, responsibilities of thecontractor, owner and other parties thatmay be part of the agreement. Insurance,bonding, definitions, schedule and timeallotment are also included. The keycomponent of interest here are the tech-nical specifications for overcoating thatare a part of the contract requirements.If you intend on using an existing mainte-nance painting specification, make surethat it is up-to-date and not simply “copy-and-pasted” pieces of specifications orbased strictly on coating manufacturers’recommendations. Because the specifi-cations are contractual, a critical reviewof the draft specification should alwaysbe performed by someone with the expe-rience and credentials to do so. This canbe the internal “paint guy (or gal),” atrusted vendor or a consultant.

Technical Specifications forOvercoatingUltimately, in the eyes of a contractor,the responsibility for the specificationwill rest with the owner, and rightly so,as the specification is part of theowner’s contract documents. When youare tasked with preparing a specifica-tion, whether you work for or areretained by the owner, where do youthink the content responsibility will lie inthe eyes of the owner?

Correct! The engineer, consultant orcoating manufacturer that prepared them.

The quality of the contract and speci-fications can contribute to a relativelysmoothly running project or can lead toMayhem (you know, that guy from theinsurance commercials).

Specification forOvercoating Structural SteelGeneralThe general section of the specificationshould include the scope of work to beperformed; definitions for words andterms used in the specification; a list of

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(type, size) and, of course, coatings.Proprietary or similar products that areto be used should also be listed. If sub-stitutions or alternates will be consid-ered, state what documentation or rea-soning must be submitted with therequest for substitution. The generalrule used when selecting an overcoatproduct is that the same resin can beapplied over the existing resin. Use oftest patches can confirm compatibility.Tie coats of penetrating epoxy sealersor a “universal” primer may be neededand also evaluated by test patch.

ExecutionThe execution section provides the detailregarding pre-cleaning requirements(pressure washing); surface contami-nants (diesel fumes); surface imperfec-tions (weld spatter, sharp corners, steel

elsewhere in the contract. Project docu-mentation and submittal requirementsshould also be included here.

For the purpose of this article, thescope will involve a small truss bridgewhere rust is to be removed, tightlyadhered coating is allowed to remainand the surfaces are to undergo spotrepairs and overcoating.

MaterialsThe materials section allows the owneror specifier to establish the quality,type and source of materials used forthe project. Among the items that maybe included in this section are abra-sives (required, permitted or excluded);cleaning agents (soaps, alkaline,degreasing); water (potable, non-potable); additives (chloride remedia-tion, corrosion inhibitors); equipment

published reference standards, testmethods, procedures and regulationsand other pertinent informational docu-ments relevant to the work. Safetyrequirements that the contractor isresponsible for, as well as the qualifica-tions of the contractor and personnelmay be included here unless addressed


Fig. 4: Spot repairs on the underside of thisbridge seemed sufficient, but later proved to beunsatisfactory.



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defects); items to be protected, andcontrol and containment of the workarea. Certain procedures or processescan be excluded (including prohibitingabrasive blast-cleaning) but otherwiseleave the means and methods to thecontractor. Use performance-based lan-guage for surface preparation, coatingapplication, quality control and repairprocedures. Note that it is a responsi-bility to state what is to be done, butensure there is a performance and/oracceptance criteria and state whatmethods or standards will be used tomeasure and test.

Pre-clean all surfaces to be preparedand painted with low-pressure water at noless than 4,000 psi to remove surfacecontaminants. Prior to pressure washing,remove bulk deposits of dirt, soil, leavesand bird droppings manually. Place all col-lected debris in containers for disposal.Supplement cleaning with brushes,brooms, rags and wiping to produce noless than a chalk rating of 8 on remainingcoating when measured in accordancewith ASTM D4214, “Standard TestMethods for Evaluating the Degree ofChalking of Exterior Paint Films.”

Surface PreparationSpot RepairsClean all areas of visible rust and corro-sion in accordance with SSPC-SP 15,“Commercial Grade Power Tool Cleaning.”Remove pack rust and crevice corrosionusing impact tools to the satisfaction ofthe project engineer. Prepare areas ofblistered, cracked and delaminated coat-ing in accordance with SSPC-SP 3,“Power Tool Cleaning.” Surface tempera-ture should be a minimum of 5 F abovethe dew point before performing surfacepreparation. Spot-abrasive blast-cleaningto SSPC-SP 6/NACE No. 3, “CommercialBlast Cleaning” would only be justified ifthere were numerous spots or locations

where the size of spots were quite largeor abundant. In such an instance, fullremoval and replacement may be a moredesirable maintenance option.

Intact, adherent coating surroundingrusted and/or degraded areas must befeathered back such that the repair

coating will extend at least 2.5 to 5centimeters (1 to 2 inches) onto theintact coating.

Soluble Salt MitigationWhen removal of soluble salts is nec-essary, the requirements are included



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in the surface preparation sectionbecause the criteria must beachieved prior to coating application.Additional surface preparation andcleaning may be required. Use of pro-prietary products may be used whensalt removal is difficult and salt levelsare high. The locations and frequency

of testing are important. In thewriter’s opinion, the most importantsurfaces to test are those that havealready exhibited corrosion and arethe most difficult to prepare. Randomtesting should also be used todemonstrate absence of solublesalts.

Coated SurfacesCoated surfaces must be cleaned usinglow-pressure water during the pre-clean-ing process. However, additional clean-ing may be appropriate if the surfaceshave become contaminated from otheroperations, such as removal of blis-tered, cracked or delaminating coating.Glossy and slick surfaces may requirescarification to aid in bonding of theovercoat. If SSPC-SP 7, “Brush-Off BlastCleaning” is warranted, the abrasivesshould be fine and the nozzle pressureshould be kept low. When thick coat-ings are present and brittle, SSPC-SP 7may damage otherwise sound coating.Use of abrasive blast-cleaning, evenbrush-off blast-cleaning, can significant-ly add to time and cost for an overcoat-ing project and should be carefully con-sidered.

Coating ApplicationAmbient ConditionsRelative humidity (RH); the temperaturesof the air, surface and material (Ta, Ts,and Tm); and the dew point (DP) are allto be considered before performingcoating application. Minimum and maxi-mum values can be established by thespecification. Alternatively, requiringthat the ambient conditions conform tothe manufacturer’s published require-ments is certainly appropriate. This canalso avoid confusion or “push-back” byapplicators when the manufacturer hasmore liberal limits than the specifica-tion. Yet, if there are sound reasons forbeing more restrictive, then by allmeans specify the limits appropriate tothe situation.

Mixing and ThinningComplying with the manufacturer’sinstructions is recommended. Thinningmay be prohibited, but when permitted,it should comply with the manufacturer’s



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recommended products for the temper-atures and/or VOC limits of the work-place. Induction time and pot life shouldbe considered based on the ambientconditions and the quantities to bemixed.

Spot ApplicationWhen application begins, the surfaceto be coated should meet the surfacepreparation standard required by thespecification. The coatings selectedfor spot application should lend them-selves to brush and roller applicationand should be applied so that the filmextends onto the feathered area ofthe intact coating. These are typicallysurface-tolerant coatings such asepoxy-mastic or moisture-cured ure-thane, among others. Penetratingepoxy sealer (100%-solids) can beused as a first coat where pack rust,crevice corrosion or difficult-to-removecorrosion is present and the spotprimer has been applied over it.Stripe coating should be performedwith the spot primer and/or tie coatwhen used. A stripe coat of the finishcoat may also be applied, particularlywhere edge corrosion exists.

Overcoat ApplicationFollowing adequate cure of the appliedspot coat, a full coat is applied. Thismay include a tie coat and finish coator a finish coat compatible with theexisting coating resin. Test patches willhelp to determine which overcoatingsystems perform better than others.The products used should provide thedesired finish (gloss, semi-gloss) andcolor(s). Brush and roller or spray appli-cation can be used depending on sur-face area, location and how protectionof other surfaces from splatter, spitsand overspray will be accomplished. Itwas mentioned earlier that spray appli-

cation may be prohibited by some own-ers or circumstances. It is worth notinghere that a full overcoat does not nec-essarily mean to all surfaces. Non-visi-ble surfaces (under deck beams anddiaphragms) may not need an additionalcoat when exposed steel is being over-coated. This is particularly true when

the major factor in maintenance paint-ing is aesthetics.

Repairs and Deficient CoatingA process for addressing coatingrepairs from mechanical damage anddefects due to preparation or applica-tion should be established. In particular,



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edges of the old coating system maylift when overcoated if thick and notfeathered, or if not tightly adhered.These require correction which may beas simple as re-applying the spot coatand/or overcoat, or in the worst cases,removal, preparation and re-applicationof the spot primer and overcoat.

Quality ControlQuality control must be exercised toachieve a completed project compliantwith the specifications, including refer-enced standards and performance cri-teria when tested or examined by themethods called for in the specification.We teach that quality control is the

responsibility of the contractor. It is;however, the contractor should realizethat control over quality is actually inthe hands of the craftsmen doing thework (be it surface preparation, mixingor applying the paint) rather than, or inaddition to, the foremen and superinten-dents at the project. The owner andengineer are obligated to clearly statethe performance required, the criteriaand the manner by which it will be mea-sured. A requirement to submit qualitycontrol reports on a regular basisshould also be included.

DemobilizationDemobilization is just as much a part ofthe project as mobilization. It has beenincluded as part of the overcoatingspecification as a place to houserequirements for leaving the site.Requirements typically include cleaningthe work and laydown areas, collectionand proper disposal of all wastes(including wastewater from low-pressurewater cleaning, if applicable) and ensur-ing no reusable materials leave the sitewith contamination when toxic materialsare involved.

ConclusionThe specification guidance providedherein cannot address every situationor circumstance; no static documentcan. The complexity associated withwhat, on the surface, may appear to bea simple spot-and-overcoat solution, hasalso hopefully been conveyed.

Overcoating specifications and meth-ods that are tried-and-true are the prog-eny of the mistakes, errors, screw-upsand mayhem that came before. Futureovercoating specifications will be supe-rior to the ones in use today simplybecause over time we will notice thescars, warts and shortcomings.

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