36 D+D AUGUST 2014

By Jayson L. Helsel, P.E., KTA-Tator Inc.

Clues to a Coating Failure

A Case of HazingA mysterious white film discolors an architectural block building.

oped and increased following rain.

In some areas the white discoloration faded or disappeared in

dry weather, but overall, much of the building remained discol-

ored.

By early winter, the building had widespread white discoloration

varying in severity. The block wall in a sheltered area at a building

entrance, for instance, had a lesser degree of white staining than

exposed areas. On another part of the building, where the anti-

graffiti coating had not been applied, the red block wasn’t discol-

ored at all.

Close examination revealed that heavier discoloration appeared

to correspond with areas of heavier application, evidenced by runs

in the coating. The consultant applied a few drops of 50 percent

hydrochloric acid on some of the heaviest discoloration, but saw no

reaction. That indicated the white discoloration wasn’t cementi-

tious or caused by efflorescence from the concrete block.

Because of the block’s irregular surface, the consultant couldn’t

perform other typical field tests such as thickness measurement

and adhesion testing. He took sample scrapings of the coating for

laboratory analysis, as well as some uncoated, unsealed split-faced

block left from the recent construction.

Laboratory Examination and TestingMicroscopic examination of samples determined that the thickness

of the coating layers ranged from approximately 1 to 2.3 mils. That

s a new transit station in a Midwestern city

neared completion in fall 2010, a whitish haze

bloomed across the building’s red, split-faced

concrete block walls.

The stains covered the walls to a height of

about 18 to 20 feet (5 to 6 meters) — the height

of the station’s recently applied anti-graffiti coating.

The coating manufacturer had recently acquired the anti-graf-

fiti product from another company, and with little experience of

the product to go on, called on an outside coatings consultant to

solve the mystery of the white haze, which appeared to be re-

lated to the coating.

Field Examination and TestingThe investigator, arriving in early winter, found that the anti-

graffiti coating wasn’t the only protective treatment on the build-

ing. Before it went on, workers had covered the entire masonry

fabric with a water-based silane sealer from the same company

that originated the anti-graffiti coating. The two products were

said to be compatible and were meant to be used together.

After the sealer cured, the consultant learned, applicators in-

stalled three coats of the water-based acrylic, non-sacrificial anti-

graffiti coating on the block walls.

The white discoloration or hazing soon appeared where the

anti-graffiti coating had been applied. The discoloration devel-

A

37

was less than expected for three coats of the anti-graffiti coating.

Based on the manufacturer’s published coverage rate of 200

square feet (19 square meters) per gallon for split-faced block and

40 percent solids by volume, one coat of the material theoretically

should yield a dry-film thickness of 3.2 mils. However, the lab

noted that it was difficult to estimate how much coating the

porous block surface might absorb.

Since the hazing and discoloration seemed to occur during wet

conditions, the consultant began with moisture-sensitivity testing.

Clues to a Coating Failure

An unknown white stain, not efflorescence, blooms uniformly across thelower reaches of an architectural block building, where an anti-graffiticoating is newly installed. Photos courtesy of KTA-Tator Inc.

This close-up photo shows the split-faced block’s irregular surface, which pre-cluded field tests of the anti-graffiti coating’s adhesion and thickness. Laboratoryexamination, however, revealed the coating to be much thinner than expected.

First he applied the silane sealer and let it dry per manufacturer’s

instructions. Then he coated the sealed block with one, two and

three coats of the anti-graffiti coating and let it cure 72 hours. He

misted the cured block with water. The block turned white imme-

diately after misting in the section with three anti-graffiti coats. It

developed a milky appearance in the section with two coats, while

the section with one coat remained mostly clear.

After the block samples dried, the consultant found that the

area with one coat, mostly clear at first, had developed minor hazi-

ness. The areas with two and three coats showed more areas with

a white or milky appearance, especially concentrated in low areas

where the coating collected during application. A nearly consis-

tent white film covered the surface of the block with three coats.

The consultant re-misted the block after another 72 hours, with

similar results. Most of the section with two coats discolored, and

those areas appeared wet, but were dry to the touch. The white

hazy film covered the three-coating section, and the entire sur-

face, though dry, looked wet.

A coated block sample that was not misted with water also ex-

hibited a hazy, but less pronounced, discoloration where the con-

sultant applied two and three coats. The section with two coats

exhibited haziness in certain areas, and the section with three

coats had a slight milky appearance. The section with one coat ex-

hibited no hazy discoloration. The discolored areas were predomi-

nant in the low sections of the block surface, where the coating

collected during application. Although these un-misted samples

38 D+D AUGUST 2014

He applied one, two and three coats of

the anti-graffiti coating to glass panels.

This method helped the investigator iso-

late the coating so he could see its per-

formance free from other factors. The

single-applied coat dried clear and ap-

peared to be in good condition. After 72

hours, a sufficient cure time according to

the product data information, he misted

the coating with water. The water ap-

peared to cause the coating to immedi-

ately wrinkle. After drying, it developed a

white, hazy discoloration. Panels with two

and three coats reacted the same way, al-

though the three-coat panel exhibited

more severe wrinkling than the other two.

This testing clearly showed that the

coating was sensitive to moisture after ap-

plication.

Next, the consultant tested the coating

on the leftover block from the project site.

A concrete block sample treated with a suspect anti-graffiti coating develops hazing shortly after beingmisted with water, then drying. Note how the milky haze develops in low spots where coating is thickest.

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did discolor and were hazy, it was far less severe than the milky

white film on the block sample with three coats that the consult-

ant misted with water.

FindingsThe laboratory testing clearly showed that the anti-graffiti coating

was sensitive to moisture. It absorbed and trapped moisture, and

turned white as a result, even after proper curing following the

product data information. Laboratory application of the system to

split-faced block samples followed by water-misting replicated

the white hazy appearance at the building site.

Additionally, by applying the coating to glass panels, the con-

sultant showed that the coating by itself quickly turned from

nearly clear to white and hazy upon moisture exposure.

The testing also demonstrated that the coating only needed

to get wet from environmental exposure to develop discol-

oration or hazing. Though there was no suggestion that coating

application occurred in wet conditions, the weather history for

39Clues to a Coating Failure

Heavier discoloration appears to correspond with areas of heavier application, evidenced here by runs in the coating.

applied silane sealer, and the porous

block’s absorption of the anti-graffiti coat-

ing, did not appear to be factors.

The investigation found that the discol-

oration and hazing resulted from applica-

tion of what appeared to be a product

unsuited to the environment in which it

was expected to function.

RecommendationsDue to the inherent problem with the anti-

graffiti coating’s moisture sensitivity, the

consultant recommended removing the

coating. He recommended methods includ-

ing dry abrasive blast cleaning with mild

abrasives, pressurized water cleaning with

hot water, and chemical stripping.

Dry abrasive blast cleaning with mild

abrasives appeared to be the most practical

method to effectively remove the coating

without damaging the block. Mild abrasives

expected to work included soft crushed

glass and glass bead media, and organic

media such as corncobs or walnut shells.

The consultant recommended low pres-

sure and increased blast distance to further

minimize chances for damage to the block

substrate.

Since the building’s owner still wanted an

anti-graffiti coating, the consultant recom-

mended another product with a successful

history in similar projects — along with tests

on representative block wall sections to ver-

ify that surface preparation and product ap-

plication would work as intended.

About the AuthorJayson Helsel is a sen-

ior coatings consultant

with KTA-Tator Inc. He

is a registered profes-

sional engineer, an

SSPC protective coat-

ings specialist, an

SSPC-certified concrete

coatings inspector and a NACE-certified

coatings inspector. At KTA, Helsel manages

coating projects, performs failure investiga-

tions and coating surveys, writes coating

specifications and is a regular instructor for

coating inspection courses. He holds a mas-

ter’s degree in chemical engineering from

the University of Michigan. D+D

40 D+D AUGUST 2014

the two fall months when application oc-

curred showed that rain fell eight days in

each month. It was likely that the coatings

got wet soon after application, if not dur-

ing.

Thicker areas of the coating developed

heavier hazing simply because more coat-

ing absorbed more water. The previously

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