WATERBORNE COATINGS FOR WATER AND WASTEWATER TREATMENTPLANTS

Tony Ippoliti, Senior Corrosion Specification SpecialistThe Sherwin-Williams Company

Indianapolis, IN

Abstract: This presentation brieflyupdates a two-part article printed inWater Engineering & Management in2001. It begins with the benefits ofwaterborne coatings and gives examplesof where they may be used.

Introduction

It is well known that service conditionsin water and wastewater treatment plantscause these facilities to experiencecorrosion often severe. It is also wellknown that the role of paints andcoatings is to protect substrates fromcorrosion and from chemical attack anddeterioration at these sites.

During the past decade or two, theprocesses performed in water andwastewater facilities have remainedbasically the same: collection/gritremoval, flocculation/coagulation,clarification, chlorination, transmission,distribution, and storage. But today,increases in plant efficiencies mean thatfar more gallons per day can be treatedusing these same processes. 1

The protective coatings applied in waterand wastewater treatment facilities havechanged little during the past 10-20years. They are basically of the samesolventborne generic classification -epoxies and urethanes and theseremain the predominant types of

coatings used. But regulations havecaused coating formulators to modifyepoxies and urethanes to reduce theirVOC content. This has beenaccomplished by adopting highervolume solids solventborne formulationsin place of lower volume solidssolventborne formulations.

With a few exceptions, VOC reductionscould be accomplished by thesubstitution of waterborne epoxies andurethanes. Further, VOC regulationshave provided the impetus foradvancements in the formulation of ALLwaterborne coatings and it is the USE ofthese waterborne coatings in water andwastewater facilities that is of interest,here.

Solventborne epoxies and urethanescontinue to be specified and applied onsurfaces where other generic waterbornecoatings will certainly provide theintended performance at reduced cost,reduced odor, reduced VOC, andreduced labor. The reasons for vary: ageneral lack of coatings knowledge, alack of knowledge of waterbornecoatings and their performanceadvancements, the use of old ,solventborne-based specifications fromprevious projects, using the same oldpaint the same old way , and resistanceto change ... regardless of theoverwhelming benefits waterbornecoatings can often provide.

Using Waterborne Coatings

Waterborne coatings have beenimproved in ways that allow them tobetter accommodate constructionschedules and to better suit maintenancepainting as materials of constructionhave changed in water and wastewatertreatment facilities. There is greater useof concrete, non-ferrous metals, andPVC/FRP that challenge old methodsand systems. These surfaces are beingprotected with waterborne coatings thathave not, traditionally, been the coatingsof choice.

One example is non-ferrous metals aluminum - as handrails that may circleclarifiers and basins. Although notusually painted, coatings for aluminummust have good adhesion qualities oversuch smooth surfaces. Waterborne washprimers are available which do notcontain the acids found in traditionalwash primers, yet offer 5B adhesionwith topcoats when tested according toASTM D3359.

Zinc-coated metals, as ductwork indewatering areas for example, have beendifficult to coat successfully with somesolventborne coatings. Saponification,resulting from the use of alkyd coatingson such surfaces, is so well known that itneeds no mention. But what should beacknowledged is that many types ofwaterborne coatings can be applieddirectly to zinc coated surfaces withoutthe risk of saponification, the need forspecial primers, the hydrocarbon odors,nor the ignition hazards from ceiling-mounted heaters.

Items made of PVC and FRP (fiberglassreinforced plastic) are also found inwater and wastewater plants. PVC is

primarily used for piping and FRP iscommonly used to fabricate smallstorage tanks. When outside, theseconstruction materials may needprotection from the sun s ultravioletlight to prevent surface deterioration andweakening. Waterborne coatings withgood adhesion and UV resistance, suchas acrylics, make a good choice for thesesubstrates. And they remain flexible.

Floors, walls, and ceilings in water andwastewater treatment plants are typicallyconcrete and masonry. Coatings forcementitious surfaces must be resistantto its alkalinity. Where concretemasonry units (CMU) are used, the firstcoating applied must be able to fill voidsand create a pinhole-free surface onwhich finish coats can be applied.Cementitious waterborne acrylic orwaterborne epoxy block fillers are thecoatings to use on these surfaces.Waterborne coatings able to seal, color,or create a protective barrier on cast-in-place concrete are also available.Waterborne floor finishes (acrylic,epoxy, urethane) have been available forsome time and can be used to protectfilter gallery walkways, for example.

Is it ever possible to successfully coatbare steel with waterborne coatings? Areview of past SSPC Proceedings willprovide positive proof that waterbornecoatings will work . Steel is still usedfor pumps and piping, storage tanks,clarifier catwalks, and other items.Waterborne primers for steel, containingcorrosion and flash rust inhibitors, arenot only available but also desirablebecause of their low odor, ease ofapplication and clean up during paintingoperations. Waterborne primers for steelare available in acrylic, epoxy, and zinc-rich formulations and each offers its

characteristic level of corrosionprotection.

Performance

If Life Cycle Estimates are to bebelieved (and accurate ones are) acomparison between a 3-coat alkydsystem and a 3-coat acrylic system canshow one example of the Life Cyclebenefits of a switch to a waterbornecoating system. See Schedule A.

Impact, abrasion, and corrosionresistance may be demanded by waterand wastewater treatment plant Ownersfor various process areas. Theseperformance levels are met through theproper selection and application ofprimers and fillers, and intermediate andtopcoats. Surfaces can be made pinhole-free to accommodate cleaning and limitbacteriological growth, floors can bemade low-slip and easy to clean, ceilingscan be made light reflective, and pipingsystems can be made to reflect the TenStates Standards for identification.Finishes can be gloss, semi-gloss, or lowsheen.

But one may ask: will these coatingsMAINTAIN their color? They will whenthey re overcoated with ultraviolet-resistant clear coats . Until veryrecently, UV resistant clear coats werenot available in waterborneformulations. For the benefit of thosewho have been asking, and as proof thatformulators continue to increase theselection and performance of waterbornecoatings, these clear coats are nowavailable. Some are proprietary andfirst-of-its kind formulations in gloss andsemi-gloss and as urethanes and acrylics.

These innovative coatings, and otherslike them, confirm that research anddevelopment funds are continuing to bespent not just to maintain and improveexisting technologies, but to broaden theappeal, performance, and use ofwaterborne coatings in water andwastewater treatment plants.

While waterborne coatings representgreat opportunity, and offer greatbenefits, they are not appropriate inevery situation. As of this writing,waterborne epoxy coatings, for example,are not suitable for the interior,immersed surfaces of drinking waterstorage tanks nor in a secondarycontainment area housing HFS acid.Care and consideration must still beexercised in the selection and applicationof APPROPRIATE waterborneprotective coatings systems. The bestway to determine if a particular coatingsystem is suitable in a given serviceenvironment is to contact your coatingsupplier or their technical supportpersonnel.

For those engaged in the specification,design, construction, and maintenance ofwater and wastewater treatment plants,who are unwilling to continue to do thesame old things in the same old ways ,waterborne coatings can provide thelevel of performance expected. Theefforts of the paints and coatingsindustry, during the past two decades,assures today s waterborne usersurprising success.

(1) Tony Ippoliti, WaterEngineering & Management, ScrantonGillette Communications, Inc. January2001 (p 34)

Schedule A. Life Cycle Comparison:

SB Primer / 2 Topcoats WB Primer / 2 TopcoatsModerate Industrial Exposure Moderate Industrial Exposure

SP 2 & 6.0 mils DFT SP 2 &6.0 mils DFT6.0 years Life Cycle 7.5 years Life Cycle

SP 6 & 6.0 mils DFT SP 6 & 6.0 mils DFT9.0 years Life Cycle 10.5 years Life Cycle

TABLE 1: Waterborne Coating Systems for interior wet/damp areas or areas with sometreatment chemical or H2S exposure.SUBSTRATE: PRIMER: INTERMEDIATE: FINISH:Concrete WB Epoxy

Filler/SealerHigh Build WB Epoxy High Build WB Epoxy

Concrete MasonryUnits (CMU)

Cementitious Acrylicor WB EpoxyFiller/Sealer

High Build WB Epoxy High Build WB Epoxy

Steel WB Rust InhibitiveEpoxy or WB ZincRich Primer

High Build WB Epoxy High Build WB Epoxy

GWB (Drywall) Suitable Primer High Build WB Epoxy High Build WB EpoxyPVC / FRP N/A High Build WB Epoxy High Build WB Epoxy

TABLE 2: Waterborne Coating Systems for general, light exposure.PRIMER INTERMEDIATE TOPCOAT **

GWB (Drywall) WB Acrylic WB Acrylic WB AcrylicConcrete MasonryUnits (CMU)

Cementitious Acrylicor WB EpoxyFiller/Sealer

WB Acrylic WB Acrylic

Zinc Coated Metalsand Aluminum

Cleaner/Etcher WB Acrylic WB Acrylic

Steel WB Acrylic or WBEpoxy Primer

WB Acrylic WB Acrylic

Cast-in-Place Concrete (fill voids asnecessary)

WB Acrylic WB Acrylic

Concrete Floors WB Epoxy Primer WB Epoxy WB Epoxy orWB Urethane

PVC/FRP N/A WB Acrylic WB Acrylic**Note: for EXTERIORS, apply WB urethane or WB Acrylic topcoats and appropriateClear Coat for extended color and gloss retention.

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