BroomFinishorBlastedSurface? C - · PDF fileASTM D 7234 (Fig. 2).20 This test method...

from biogenic sulfide corrosion.6,7,8 As aresult, high-performance lining systemshave emerged specifically for severewastewater environments.9

The protective coatings industry hasalso paid special attention to the repairof concrete using cementitious resurfac-ing mortars—both thin overlays andshallow depth replacements—beforeapplying high-performance linings.10

Resurfacing improves the film quality ofa protective coating by providing a con-tiguous surface for topcoating andensures a monolithic protective barrierfilm at a specified nominal thickness.Because of this expanding repair mar-ket, cementitious resurfacing materialsand repair methods are being intro-duced at an increasing rate for useunder high-performance protective coat-ings. Unfortunately, as the repair marketexpands, one result has been conflictingmanufacturers’ instructions and devia-

32 www.paintsquare.comJ P C L S e p t e m b e r 2 0 0 9

oncrete is inherently durableand is used extensively inmunicipal wastewater con-struction.1 The deteriorationof concrete and reduction ofits service life can result, how-

ever, when exposed to conditions fre-quently found within these environ-ments including abrasion, corrosion ofsteel reinforcement, and biogenic sulfidecorrosion.2,3 The rehabilitation and pro-tection of concrete within these aggres-sive exposure conditions has consistent-ly been a challenge given the fact that nohydraulic cement, regardless of its com-position, will long withstand a pH 3 orlower.4,5 This problem is exacerbated byincreasing concentrations of hydrogensulfide (H2S) gas rising beyond the levelsprotected by traditional protective barri-er systems, ultimately negating the pro-tection of the cementitious substrate

tions from many industry standardsregarding the curing, finishing andpreparation (e.g., broom finish vs. blast-ed surface) of various cementitiousmaterials, even those that are generical-ly similar. In fact, commonly, manufac-turers of repair mortars recommend abroom finish to create a “profiled” sur-face before applying the lining. Less com-monly, manufacturers recommend thatthe cementitious mortars be blastcleaned or otherwise mechanically pro-filed to impart a mechanical profilebefore applying the lining. In the follow-ing article, the authors summarize theresults of an investigation to quantita-tively assess adhesion of a protectivelining when applied to a broom finishsurface versus a mechanically profiledconcrete surface.

Background on AdhesionThe Importance of Surface Profile

for Lining AdhesionWhen applying a high-performance pro-tective lining directly to new concrete, it

PreparingRepair Mortarsfor Wastewater Service:

By Vaughn O’Dea andRick Schwab, Tnemec Company, Inc.

Broom Finish or Blasted Surface?Broom Finish or Blasted Surface?

C

Editor’s Note: This article is based on a paperpresented at PACE 2009, the joint conference ofSSPC and PDCA, held February 15-18, 2009, inNew Orleans, LA.

Allphotoscourtesyoftheauthors

adequate surface for lining adhesion. It ispossible that like concrete, cementitiousrepair materials form a laitance layerthat could similarly interfere with theadhesion of the lining and the success ofthe complete repair system.

Unfortunately, the presence and thedepth of laitance typically cannot bedetected visually, but must neverthelessbe removed to create a surface profilethat will enhance lining adhesion.

Mechanically Profiled Surfaceand Laitance

The value of a mechanically profiled con-crete surface before applying a liningreflects the prevailing view that theremoval of the laitance is paramount toachieving maximum bond strength of thelining.11,12 Moreover, a recent study by

resurfacing composites for use underhigh-performance protective linings.Specifiers and users of cementitiousrepair materials would clearly benefitfrom information that quantifies thebond zone strength of popular cementi-tious mortars.

Laitance and AdhesionNew concrete—along with other cemen-titious substrates—commonly has aweak surface layer, called laitance, result-ing from use of too high a water/cementratio, drawing of fines to the surface dur-ing surface finishing, the exudation offines with bleed water, or improper cur-ing. Laitance will have a weaker tensilestrength than the rest of the concretesubstrate, and if not removed, will weak-en the concrete’s ability to provide an

is widely accepted that profiling increas-es the surface area available for bondingthe protective lining to the concrete sub-strate. Profiling also enhances themechanical adhesion at the con-crete/coating interface and helps the lin-ing resist peeling and shear forces. (Thispremise excludes the effects of a chemi-cal adhesion bond obtainable by somepolymer-modified repair mortars.) Itseems logical that mechanically profilinga cementitious resurfacing mortar wouldoffer similar benefits to the lining perfor-mance. But because broom finishing isstill common in wastewater repair, thequestion arises: does a broom finish pro-file provide similar adhesive propertiesto those of a blast cleaned (mechanicallyprofiled) surface (a more expensive andtime consuming process)?

Tensile Strength and AdhesionTo be effective in the rehabilitation andprotection of concrete, a protective sys-tem, which includes both the cementi-tious repair mortar and protective lining,must develop and maintain adhesive andcohesive direct tensile strengths greaterthan the surface tensile strength of theparent concrete. This criterion ensuresthat the system is able to withstand thestresses imposed on, and the processesof deterioration associated with, severewastewater environments.

A cementitious resurfacer exhibitingweaker surface tensile strength proper-ties than the parent concrete surfacepotentially compromises the integrity ofthe protective system and is prone tocause the system to fail prematurely. Therepair mortar’s surface tensile strength,or bond zone strength, which refers tothe surface of the mortar that will be incontact with the coating, is not as wellunderstood as it should be. Because ofthe diverse finishing/preparation recom-mendations oftentimes encounteredwithin the wastewater repair industry,there is a need for a more comprehen-sive understanding of the general surfacetensile behavior of the various hydraulic

33www.paintsquare.com J P C L S e p t e m b e r 2 0 0 9

Measuring Bond StrengthIt is well established that the development and maintenance of a sound bond between the coat-ing and the concrete substrate is an essential requirement for heavy-duty, high-performance pro-tective lining systems. Tensile pull-off tests are becoming increasingly favored in laboratory andsite quality control/quality assurance testing. Various industry consensus guidelines recommendthat pull-off adhesion tensile testing should result in substrate (parent) concrete cohesive failureas most desirable for coatings applied to concrete. In this case, the pull-off stress (adhesion) isconsidered exceeding the direct tensile strength of the substrate concrete. There are two popularASTM testing methods describing tensile pull-off testing.ASTM D 7234 Standard Test Method for Pull-Off Adhesion Strength of Coatings on Concrete

Using Portable Pull-Off Adhesion Testers (formerly recommended for coatings on concreteunder ASTM D 4541) stipulates scoring of the coating down to the surface of the substrate. Asreasonably interpreted, the substrate is considered any cementitious material (i.e., cast concretesubstrate, cementitious repair mortar, etc.). This “limited” scoring, however, causes stress non-uniformity due to the concentration of tensile stress at the dolly periphery at its interface with thesubstrate. This leads to a corresponding increase in the substrate stress at this position, whichextends into the concrete (or cementitious mortar) beyond the dolly perimeter. This may providean explanation to the small degree of ‘overbreak’, whereby the tensile stress extends beyond thedolly perimeter and results in higher measured tensile strength of the cementitious repair mor-tars (often exceeding the actual tensile strength values of the concrete substrate).ASTM C 1583/C 1583M Standard Test Method for Tensile Strength of Concrete Surfaces and

the Bond Strength or Tensile Strength of Concrete Repair and Overlay Materials by DirectTension (Pull-off Method), on the other hand, requires partial core drilling through the cementi-tious mortar and into the concrete substrate a minimum one-half inch. Partial coring reducesstress variation and ensures a reasonably uniform distribution of concrete stress over the fulldepth of the coring. Unlike ASTM D 7234, the failure plane is usually located at the end of thedrilling core – reflecting actual direct tensile strength. The failure load (measured tensilestrength) tends to be slightly lower when using this method compared to ASTM D 7234.

the author found that most cementi-tious repair mortars commonly usedfor wastewater rehabilitationincreased their surface tensile proper-ties when externally cured, that is,with a curing membrane applied inaccordance with ACI 308R.13,14 Thestudy further concluded that the adhe-sion of a high-performance protectivelining was maximized when the sur-face of these repair mortars wasmechanically profiled, which removedthe laitance layer and curing com-pound, where present. (Adhesion ofthe lining over a broom-finished sur-face was not addressed in the earlierstudy.)

Broom Finished Surface Profileand Laitance

Research suggests the broom finish pro-file for linings may have originated fromthe concrete repair industry practices(when no lining is involved) to improvethe bond of the mortar to itself. Whenrehabilitating concrete using cementi-tious mortars in multiple lifts, it is com-mon practice to thoroughly roughen,cross hatch, or rake the surface of thefirst lift of the repair mortar to promoteadditional mechanical bond for the sub-sequent lift (Fig. 1).15-18 Despite thecommon use of broom finishing to pro-file repair mortar before lining applica-tion, the authors found no literaturesuggesting whether or not this finish-ing technique categorically alleviatesthe formation of laitance, the weaksurface layer that may affect the bond-ing of a protective lining system.

Objectives of the StudyBecause of the lack of availableresearch on repair mortars and lai-tance, the study described in this arti-cle was undertaken to address the fol-lowing questions. Is it possible that abroom-finished surface eliminates theformation of a laitance layer on cemen-titious repair mortars? And is the sur-face tensile strength of a broom-fin-

properly receive a high-performancelining?

ExperimentalMethodCementitious Mortars

Cementitious mortars using ingredi-ents that most closely match those ofconcrete are the best choices for repairmaterials.17 Based upon this principle,the authors surveyed 100 wastewaterprojects and found the four cementi-tious repair composites most common-ly specified for use in concrete repairunder protective lining systems.19

These cementitious composites aregenerically classified as:• epoxy-modified cementitious mor-tars,• acrylic-modified cementitious mor-tars,• portland-based cementitious mor-


Product Cementitious Minimum Maximum Mfgr’s Recommended Mfgr’s ACIDesignation Mortar Thickness Thickness Finishing External Curing

Type Technique(s) Requirements

Mortar 1 Epoxy-modified 1/16" 1/4" Rubber float, steel Nonetrowel, masons brush

Mortar 2 Epoxy-modified 1/16" 1/8" Rubber float, steel Nonetrowel, masons brush

Mortar 3 Epoxy-modified 1/16" 1" Conventional concrete Nonefinishing tools

Mortar 4A Acrylic-modified 1/4" 2" Wooden or rubber ACI 308float, trowel

Mortar 5 Acrylic-modified 1/4" 3/4" Trowel ACI 308

Mortar 6 Acrylic-modified 1/8" 1.5" Wooden or rubber ACI 308float, trowel

Mortar 7 Portland-based 1/4" 1/2" Broom <5-8 hrs applycoating;>8 hrs ACI

Mortar 8 Portland-based 3/8" 2" Wooden or rubber ACI 308float, trowel

Mortar 9 Portland-based 3/8" 1.5" Wooden or rubber ACI 308float, trowel

Mortar 10 Calcium 1/2" 3" Broom ACI 308Aluminate-based

Mortar 11 Calcium 1/2" 1" Broom <70% R.H.Aluminate-based Curing Required;

>70% None

Mortar 12 Calcium 1/2" 3" Trowel or broom Not listedAluminate-based

Table 1: Cementitious Resurfacing Materials Included in Surface Bond Strength Evaluation

ished surface equal to or greater thanthe surface tensile strength of the par-ent concrete so that the mortar can

Fig. 1: Typical broom-finished surface

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tars, and• calcium aluminate-based cementi-tious mortars

Three commercially available repairmaterials from each generic compositetype were procured for this researchstudy. The mortars vary in their respec-tive surface preparation requirements,minimum application thicknesses, curingrequirements (and durations), surface fin-ishing technique(s), and subsequent sur-face preparation required to receive ahigh-performance coating (Table 1 onp. 34). Testing matrices were developedto compare the surface tensile propertiesof the twelve mortars when applied attheir respective minimum recommendedthickness.

Bond Strength TestingThe surface tensile strength propertiesof the selected repair materials–withand without a high-performance top-coat– were assessed in accordance withASTM D 7234 (Fig. 2).20 This testmethod delineates a procedure for eval-uating the direct tensile strength (com-monly referred to as adhesion) of acoating on concrete (or other cementi-tious substrate). The test determineseither the greatest perpendicular force(normal stress, σ) that a surface areacan bear before a plug of material isdetached.21 The uniaxial testing instru-ment used for this tensile strengthassessment was the self-aligning tensilepull-off adhesion tester using 50-mm (2-in.) diameter dollies. Tension wasapplied until failure was achieved, andthe maximum normal stress and thelocation of the failure were recorded.The peak loading for this instrumentusing 50-mm diameter loading fixtures(dollies) after conversion is 560 psi. (Seesidebar on p. 33)

Failure occurs along the weakestplane within the system. The testresults were reported as determined byobserving the bottom of the dollies withthe following designations:• Concrete substrate: A

• Mortar: B• Epoxy topcoat: C (where applied)• Adhesive (glue): Y• Loading Fixture (Dolly): Z

Cohesive failures and the percent ofeach were denoted as A, B, C, or Y.Adhesive failures by the interfaces atwhich they occur where denoted A/B,B/C, C/Y, etc.• Concrete Substrate Panels: In labora-tory work it is common to produce ahigh strength substrate to maximize thechance of obtaining adhesive bond fail-ure as opposed to a tensile (cohesive)failure of the concrete substrate. Non-reinforced concrete panels were cast 24in. x 24 in. x 2 in. to provide a commonsubstrate for testing. The concrete was ahigh-strength 5,500 psi Portland Type Idesign mix conforming to ASTM C387.22 The top faces of the panels(exposed side) were finished and mem-brane cured per ACI 308R14 using twocoats of an acrylic membrane-curingcompound conforming to the require-ments of ASTM C 309.23 The concretepanels were both cast and cured in acontrolled laboratory environment (72F and 48% RH) and remained in theforms for 7 days; the panels weredemolded and maintained in laboratoryconditions. After a period of 28-days,the concrete panels were prepared bydry-abrasive blasting the top face of thepanels to an SSPC-SP 13/NACE No. 6surface condition,12 and achieving anICRI-CSP5 surface profile.24 The con-


crete substrate panels serve as the par-ent concrete for our study.• Epoxy Coating (EP): A high-build,100% solids, two-component, high-func-tionality amine epoxy was used as a rep-resentative high-performance protectivelining used over cementitious mortars inaggressive environments. The epoxy wasapplied in a single coat to a dry filmthickness (DFT) of 30 mils.

This commercially available high-per-formance lining is recommended for useover concrete and steel in highly corro-sive wastewater and other chemicallyaggressive environments. The suggestedthickness range for this product is30–80 mils DFT. When applied directlyto properly prepared concrete, the tech-nical data sheet indicates that the adhe-sion exceeds the tensile strength of con-crete (cohesive concrete failure).• Concrete Control Panel (CCP): A sin-gle, randomly selected concrete sub-strate panel was withheld for use as acontrol in accordance with the samplingprocedures outlined in ASTM D 3665.25

The concrete panel was 24 in. x 24 in. x2 in., finished, membrane cured, and pre-pared consistent with the panels andmethods described above.

The upper-half of the concrete panel—Section A (Fig. 3 on p. 37)—was desig-nated as the Concrete Control Panel-A(CCP-A) and remained unchanged fromthe surface preparation condition (SSPC-SP 13/NACE No. 6, ICRI-CSP5). CCP-Awas used to determine the tensile

Fig. 2: Tensile strength testing, ASTM D 7234

filed coated mortar test panels wouldbe compared to CCP-B to determinewhether or not the coated cementitiousrepair mortar exhibits properties equalto the coated concrete control, and iffinishing technique affects the sound-ness of the surface of the repair mortarand its ability to properly accept thecoating.

Testing MatricesTwo testing matrices were developed todetermine which surface finishing tech-nique (e.g., blasted surface or broom fin-ish) maximizes adhesion of the protec-tive lining applied to the twelve repairmortars. The results were then com-


strength of the concrete control panel.The lower half of the concrete panelsection—denoted CCP-B—was topcoat-ed with 30 mils’ DFT of the epoxy coat-ing and allowed to cure for 7 days.After the 7-day cure, sections A and Bwere evaluated for bond strength usingmethods outlined in ASTM D 7234using the adhesion tester with 50-mmdiameter dollies (Figs. 4a, 4b, and 4c onp. 38). The CCP-B was used to deter-mine the tensile strength of the repre-sentative parent concrete substrateusing the uniaxial testing instrumentwhen a 100% solids epoxy barrier sys-tem was applied directly to the pre-pared substrate. Both CCP-A and CCP-B serve as the control for this study.The baseline tensile adhesion values areoutlined in Fig. 3. As Fig. 3 shows, inthe tensile strength tests, all failures ofthe lined concrete were cohesive,occurring within the concrete, not with-in the lining or at the lining-concreteinterface. Hence, as indicated in the lin-ing manufacturer’s data sheet, the liningadhesion exceeded the tensile strengthof the concrete substrate. These resultsconfirm that proper preparation andapplication procedures were followed.

After the tests, the bond strength ofbroom-finished and mechanically pro-

pared to the tensile strength of CCP-B,which represents a coating applieddirectly to properly prepared concrete.• Mechanically Profiled SurfaceMatrix: This testing matrix compriseseight quadrants (concrete panel sec-tions) that compare the bond strengthsof the twelve repair mortars by evalu-ating the influences of curing/no cur-ing, mechanical preparation/no prepa-ration, and topcoating/no topcoatingwith a high-performance lining system(Fig. 5 on p. 38). Excerpts from theresearch study on the effects of curingand mechanically profiling thesecementitious repair mortars are pre-sented below.13

Fig. 3: Concrete control panel–tensile strength

Baseline: Concrete Tensile Strength

Baseline: Coating directlyto Concrete

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received no external curing; the righthalf of the panel—Sections D, F, H, J—were cured using two coats of an acryliccuring compound in accordance withACI 308R.

After the proper curing (hydration)period for each respective cementitiousmortar, the lower sections G, H, I, Jwere blasted to an SSPC-SP 13/NACE6, ICRI-CSP3 profile to remove the cur-ing compound (where used) and weaklaitance layer of the mortar (where pre-

sent). The 100% solids epoxy coatingwas immediately applied to the middlesections E, F, G, H of the panel andallowed to cure for an additional 7 days.

Following the 7 days’ cure of theepoxy coating, each panel section wastested for bond strength using ASTM D7234 adhesion tester using 50-mmdiameter dollies. Each section was test-ed in triplicate, and an average valuewas reported for the respective mor-tars.• Broom-Finished Surface Matrix: Atesting matrix composed of four quad-rants (concrete panel sections) wasestablished to assess the effects ofbroom finishing of the 12 repair mor-tars with and without topcoating. Eachpanel section compared the surfacebond strength of the mortar uponreceiving a broom finish by evaluatingboth the influences of curing/not cur-

ing and topcoating/not topcoating witha high-performance lining on therepaired surface (Fig. 6 on p. 40).

Each of the twelve selected cementi-tious mortars was applied to the con-crete substrate panels at their respectiveminimum recommended thickness. Theconcrete panels were first dampenedwith potable water to achieve a saturat-ed surface dry (SSD) condition. A scrubcoat of each mortar was then applied tothe concrete panel followed by the

immediate application using a rubberfloat. The mortars were finished using amason’s brush to produce a broom finishprofile. In order to test the effect of mor-tar hydration with and without externalcuring, an acrylic membrane-curing com-pound was applied to half of the mortar(Fig. 6 on p. 40).

The left half of the concrete panel—Sections K, M—received no external cur-ing; the right half of the panel—SectionsL, N—were cured using two coats of anacrylic curing compound in accordancewith ACI 308R. Upon the proper curing(hydration) period for each respectivecementitious mortar, the 100% solidsepoxy coating was applied directly tothe lower sections M, N of the panel andallowed to cure for an additional 7 days.Following the 7 days’ cure of the epoxycoating, each panel section was tested forbond strength using ASTM D 7234

Each of the twelve selected cementi-tious mortars was applied to the con-crete substrate panels at their respec-tive minimum recommended thickness.The concrete panels were first damp-ened with potable water to achieve asaturated surface dry (SSD) condition.A scrub coat of each mortar was thenapplied to the prepared concrete sub-strate panel followed by the immediateapplication using a rubber float. Themortars were finished using a steeltrowel to obtain a smooth, uniform fin-ish. In order to test the effect of mortarhydration with and without externalcuring, an acrylic membrane-curingcompound was applied to half of themortar (Fig. 5). The left half of the con-crete panel—Sections C, E, G, I—


Fig. 4a: Testing surface tensile strengthproperties using 50-mm-diameter dollies in

accordance with ASTM D 7234

Fig. 4b: Testing surface tensile strengthproperties of Concrete Control Panel A

(SSPC-SP 13/NACE No. 6, ICRI-CSP5 preparedconcrete panel) using 50-mm-diameter dollies in

accordance with ASTM D 7234.

Fig. 4c: Evaluating surface tensile strengthproperties of Concrete Control Panel B.

Fig. 5: Bond strength matrix—trowel finished/mechanically profiled

1Cementitious Resurfacing Mortars, Refer to Table 1.2Mortar surface preparation to produce an ICRI-CSP3 surface profile.

Optimum Adhesion: Concrete Panel Section Hdetermined to yield optimum bond strength

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adhesion tester using 50-mm diameterdollies (Figs. 7a, 7b, and 7c on p. 40).

AnalysisBlasted (Mechanically Profiled)

Surface MatrixOf the mechanically prepared sections,Concrete Panel Section H (membranecured and blasted profile) achieved themaximum bond strength when topcoat-ed with a protective lining system. Thisis not entirely unexpected given that liq-uid membrane-curing compounds pre-vent the loss of moisture from the mor-tar, thereby allowing the development ofsurface tensile strength properties.Membrane curing is the most practicalmethod of curing vertically- and over-head-placed repair mortars common towastewater rehabilitation where job con-ditions are not favorable for wet-curingin accordance with ACI 308R. What’smore, membrane curing compoundsmust be removed prior to the applica-tion of the lining system in accordancewith guidelines of the protective coat-ings industry.12

Broom-Finished Surface MatrixOf the broom-finished sections, theresults for the twelve cementitiousrepair mortars suggest that ConcretePanel Section M (broom-finished profileand no membrane curing) achieved themaximum mortar surface bond strengthwhen topcoated with a protective liningsystem. A few of the mortars actuallyyielded higher adhesion values inConcrete Panel Section N (broom fin-ished and membrane curing compound).Upon closer examination, it is plausiblethat the anomalous improvement in ten-sile strength derived from proper curingexceeded any diminished bonding of thelining system to the mortar by the pres-ence of the membrane “bond breaker.”Nevertheless, when canvassing the can-didate repair mortars used in this study,it appears that a broom-finished surfaceis not recommended to receive a mem-brane curing compound if topcoated


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The results of these testing matricescan now be evaluated to determinewhich surface finish optimizes the adhe-sion of a high-performance lining to acementitious repair mortar. The surfacetensile strengths of Concrete PanelSection H (Prep/Coat) and ConcretePanel Section M (Broom Finish/Coat)have been juxtaposed in Figs. 8–11(p. 42), along with the Concrete ControlPanel B (CCP-B). Recall, the optimumsurface tensile strength (pull-off adhe-sion) value for coatings over mortar testpanels in our study is greater than orequal to the adhesion of a high-perfor-mance protective lining applied directlyto properly prepared concrete (CCP-B).The baseline coating pull-off adhesionfor CCP-B for use in our study, is 538psi (Fig. 3).

Tensile Strength Comparisons ofMortar Panel Sections H vs. M

For each of the four repair compositetypes tested, Figs. 8–11 compare thecoating pull-off adhesion values of PanelH (mechanical preparation) against thoseof Panel M (broom finish). Figures 8–11also show the coating adhesion values ofpanels H and M relative to 538 psi forCCP-B, our baseline coating adhesionvalue.

ConclusionsOur findings indicate that a blasted(mechanically profiled) surface offerssuperior adhesion to that of a broom-fin-ished (profiled) surface when preparingcementitious repair mortars to receivehigh-performance lining systems. In sum,

7 of the 12 mechanically profiled panelshad surface tensile strengths equal to orgreater than that of properly preparedconcrete, as indicated by the coatingpull-off adhesion values in Figs. 8–11.In contrast, 8 of the 12 broom-finishedmortars yielded near-surface tensilestrengths significantly lower than thatof properly prepared concrete..Adhesion of coatings over most broom-finished mortars didn’t even meet thebenchmark surface tensile strength 538psi of CCP-B Control for the optimumbonding of the lining system. Based onthe coating adhesion values, the epoxycementitious composites were the onlymortars that, when broom finished andmechanically profiled, exhibited tensilestrengths comparable to each other andto CCP-B.

Further, it was concluded a broom-fin-ished surface generally forms a weakupper surface (laitance) layer on themajority of the cementitious compositestested in this study. This conclusion wasdrawn from observing a clear pattern ofpreferential failure in this surface zone,which indicates that the repair material,when broom finished, was generally theweakest link in the repair system. (Anexception to this finding was the epoxycementitious composite, possiblybecause the epoxy polymerization pre-vents the formation of the laitance layer.)A laitance layer manifests as a weak-ened or decreased surface tensilestrength compared to properly preparedcementitious mortar, and requiresremoval in accordance with standardsset forth by the protective coatingsindustry.11,12

It should be noted that this study con-trasted mortar surfaces prepared to anICRI-CSP3 profile only to detect a weakupper surface (laitance) layer. Greatersurface rugosity (amplitude) may berequired by the coatings manufacturerfor long-term adhesion performancewithin wastewater environments.

Buyers beware! Beware of exaggerat-ed claims of experience with surface


with protective lining systems. That is,a curing membrane is supposed to beremoved before coating; otherwise, themembrane may form an adhesion “bondbreaker” between the mortar and thetopcoat. The advantages of the broom-finished profile would be lost, however,during the required removal of the cur-ing compound.

Fig. 6: Bond strength matrix—broom finished

Fig. 7c: Surface tensile strength failure planeswere determined by observing the bottom

of the 50-mm dollies.

Fig. 7b: Lining over broom-finished mortar

Fig. 7a: Typical broom finish profile using mason’s brush

1Cementitious Resurfacing Mortars, Refer to Table 1.

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finishing of cementitious repair materials. Beware of anecdotal evi-dence as means of a repair mortar’s capability. Beware of crotchetsor other forms of unorthodox experience as evidence of success.Instead, request that manufacturers submit testing of compatibilityof the entire system in accordance with industry consensus stan-dards. Request that manufacturers provide laboratory testing tosubstantiate surface finishing and preparation requirements whentopcoated with high-performance lining systems. Require manufac-turers to provide clear instructions for curing, finishing, and prepa-ration in application instructions and on component labels ofcementitious repair materials. And lastly, be diligent and performtesting of onsite mock-ups of candidate cementitious repair mortarswhen topcoated with high-performance protective lining systems.

References1. Neville, A.M. Properties of Concrete. Fourth Edition., J. Wiley,

New York, NY 1995. 2. Nixon, R.A., “Deterioration of Wastewater Treatment and

Collection System Assets: Knowing Where and How to Look,”(PACE 2006 Conference Proceedings), February 2006.

3. O’Dea, Vaughn, “Protecting Wastewater Structures FromBiogenic Sulfide Corrosion,” JPCL (October 2007), pp. 52-57.

4. ACI Committee 201, “Guide to Durable Concrete (ACI201.2R-01),” American Concrete Institute, Farmington Hills,MI, 2001, 41 pp.

5. Bowker, Robert P.G., et al. Odor and Corrosion Control inSanitary Sewerage Systems and Treatment Plants. USA: NoyesData Corporation, 1989.

6. Briand, Remi and R. A. Nixon “A Novel Analytical Approachfor Eval-uating Protective Coatings Perform-ance inWastewater Environments,” (WEFTEC 2003 ConferenceProceedings), October 2003.

7. Tnemec Company Inc. “Technical Bulletin 03-41R2: A NovelApproach for Evaluating Protective Coatings Performance inWastewater Environments,” Kansas City: Tnemec Company,Inc., 2006.

Fig. 8: Epoxy-modified cementitious mortars

Fig. 9: Acrylic-modified cementitious mortars

Fig. 10: Portland-based cementitious mortars

Fig. 11: Calcium aluminate-based cementitious mortars

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8. O’Dea, et al, “Assessing Coatings andLinings for Wastewater: AcceleratedTest Evaluates Resistance to SevereExposures,” JPCL, (April 2008), pp.44-57.

9. O’Dea, Vaughn, “Lining PreventsBiogenic Sulfide Corrosion inWastewater Systems,” MP (May2007), pp. 36-40.

10. O’Dea, Vaughn, “Preventing Bughole-Induced Outgassing,” JPCL(January 2007), pp. 86-88.

11. ASTM D4259, “Standard Practice for Abrading Concrete.” (West Conshohocken, PA: ASTM).

12. SSPC-SP13/NACE No. 6, “Surface Preparation of Concrete,” (Pittsburgh, PA: SSPC, and

Houston, TX: NACE).13. O’Dea, Vaughn, “Bond Strength

Testing of Commercially Available Cementitious Resurfacers Used for Thin-Patch Repairs of Concrete in Wastewater Environments,”Presented at the ICRI Fall Convention, Las Vegas, Nevada, USA, (November 2007).

14. ACI Committee 308, “Standard Practice for Curing Concrete (ACI 308R-01),” American Concrete Institute, Farmington Hills, MI, 2001, 31 pp.

15. ACI Committee E 706, “Vertical and Overhead Spall Repair by Hand Application (ACI RAP-06),” American Concrete Institute, Farmington Hills, MI, 2006, 5 pp.

16. ACI Committee 506, “Guide to Shotcrete (ACI 506R-05),” American Concrete Institute, Farmington Hills, MI, 2005, 40 pp.

17. ACI Committee 546, “Concrete Repair Guide (ACI 546R-04),” American Concrete Institute, Farmington Hills, MI, 2004, 53 pp.

18. Emmons, Peter H. Concrete Repair and Maintenance Illustrated: Problem Analysis, Repair Strategy, Techniques. USA: R.S. Means Company, 1994.

19. “Dodge.” McGraw Hill Construction Network. Online. March 2006. Available: www.construction.com.

20. ASTM D 7234-05, “Standard Test Method for Pull-off Strength of Coatings on Concrete Using Portable Adhesion Testers,” (West Conshohocken, PA: ASTM).

21. Koleske, Joseph V., “Mechanical Properties of Solid Coatings,” Encyclopedia of Analytical Chemistry, John Wiley & Sons, 2000.

22. ASTM C 387, “Standard Specification for Packaged, Dry, Combined Materials for Mortar and Concrete” (West Conshohocken, PA: ASTM).

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http://www.PreTox.com

23. ASTM C 309, “Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete” (West Conshohocken, PA: ASTM).

24. ICRI Technical Guideline No. 310.2,“Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays” (Des Plaines, IL: ICRI).

25. ASTM D 3665, “Standard Practice for Random Sampling of Construction Materials” (West Conshohocken, PA: ASTM).

Vaughn O’Dea is

Director of Sales,

Water &

Wastewater, for

Tnemec

Company, Inc.,

where he is

responsible for

strategic sales, marketing, and techni-

cal initiatives. O’Dea joined Tnemec in

2003 as a senior technical service rep-

resentative specializing in epoxy tech-

nology development, product failure

analysis, specification review, and

internal and external technical devel-

opment. He is an SSPC Protective

Coatings Specialist, a NACE-certified

Coatings Inspector, and a NACE-certi-

fied Corrosion Technician. He has writ-

ten numerous technical reports and

articles for various industry journals,

including JPCL. He is active in thetechnical committees of both NACE

International and SSPC: The Society

for Protective Coatings and is a mem-

ber of AWWA, WEF, ACI, ICRI,

NASSCO, and APWA. He is a con-

tributing Editor for JPCL. He won aJPCL Editors’ Award in 2008.

JPCL

J P C L S e p t e m b e r 2 0 0 9 45www.paintsquare.com

Rick Schwab has

35 years of experi-

ence with Tnemec

Company. As

Product Support/

Quality Control

Manager, he is in

charge of the com-

pany’s quality control procedures and

testing laboratory as well as trou-

bleshooting on the production floor. He

has been involved with ASTM for 10

years, including work with the D01.46

industrial coatings committee and the

accelerated testing committee.


http://www.rbwe.com

Jotun Paints, Inc.P. O. Box 159 • Belle Chasse, LA 70037 • USAToll Free: 800.229.3538 • Fax: 504.394.3726

www.jotun.com/us


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