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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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