This document discusses the complex properties of concrete and how to properly paint it. It explains that concrete is an ideal transmitter of moisture due to capillary action, and will try to equalize temperature and humidity on both sides. This can cause issues for paint adhesion and moisture-related problems. The document also summarizes the history of solvent-based and water-based concrete stains, and how more permeable water-based stains can lead to failures from efflorescence. It recommends using a pore-blocking sealer prior to painting to protect the concrete from moisture and efflorescence.

1. 8 SSECONDECOND CCOATOAT — SPRING 2007
Before you can understand the problems associ-
ated with the painting of concrete, you have to un-
derstand the surface itself.
What are precast wall panels?
They are 8’, 10’ or 12’ wide concrete wall panels
that are poured off-site at a factory. Sandwiched in
the concrete is a sheet of expanded polystyrene,
which is a thermal insulation. To give the panel
strength, pre-tensioned wire cables are placed
prior to the pouring of the concrete. The panels are
shipped to the jobsite via truck and erected atop
the building footing. Do not confuse precast with
tilt-up wall panels which are cast on site and re-
quire different painting procedures.
In the ‘70s and ‘80s the product of choice for
painting precast was a methyl methacrylate sol-
vent stain. This product had excellent color reten-
tion, longevity and penetrated concrete for a
tenacious bond. Invariably all precast manufac-
tures recommended the product as it was problem-
free and it enhanced their panels. Soon, most ar-
chitects were specifying the product. Two separate
coats of product provided trouble-free color on the
wall panels for a minimum of 10 years.
But the solvent product was to meet its demise.
On September 11, 1998 the Environmental Protec-
tion Agency passed a final rule that set new stan-
dards for the Volatile Organic Compound Emission
(VOC). This final rule was based on the determina-
tion that emissions from the solvent-based coating
had the potential to cause or contribute negatively
to the ozone levels that violate national air quality
standards.
The on-going regulatory demands for lower VOC
paints have required manufacturers to continually
reformulate or simply let old product lines die. In
the northeastern portion of the country, many sol-
vent-based products have been eliminated because
of ever-tightening regulations.
Sooner or later environmental concerns will
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The Complex Properties
of Concrete
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CONTINUED

2. 9SPRING 2007 — SSECONDECOND CCOATOAT
The following are actual examples of failures investigated
due to efflorescence.
Precast wall panels were
set in the middle of October
and caulked two weeks later.
The panels were painted in
early November before the
roof was installed. The
building was enclosed and
heated by mid-January and
the floor was poured in
February. There was no place
for the moisture to escape, but
through the walls.
One coat of paint
instead of the
required two was
applied. Within
three months
efflorescence was
evident in the
coating.
The irrigation sprinkler system was placed so
the building was constantly drenched every time the
sprinkler system was activated. [Inset photo is a
close up of the problem.]
The roof drained to gutters and downspouts. The
downspouts were left off until after the painter
completed the wall. The problem was isolated to the
area beneath the gutter opening. The rainwater
flooded that area where the eventual downspout was
to be placed. Even though the wall appeared to be
dry, the moisture activated the soluble substances
and eventually migrated to the surface, pushing the
paint off.
No gutters were placeed on the rear of
the building where the roof drained. Prior
to painting, the rear wall was power
washed to remove a tanish substance
(efflorescence). By the following summer,
the coating was peeling in sheets while
the other three elevations did not exhibit
the problem.
Grade Line Wicking —
Moisture will ‘wick up’ inside
the concrete from below grade
and cause failures at the
grade line.
Deep tone colors will show failure before light
tone or white buildings, as the color of the
efflorescence trapped in the paint becomes a
white/tan color.
A building was painted in
late October, and no interior
floor was installed. The
interior was kept at 40o
F
throughout the winter, making
it a literal rainforest.
Areas of solid concrete panel
(no insulation) will typically show
efflorescence prior to insulated
areas due to high amounts of
soluble substance.
Free standing panels (with no
interior warm side) are also subject to
problems.
Bug holes in
the wall panel
will allow rain
and water easy
access to the
interior of the
panel.

3. 10 SSECONDECOND CCOATOAT — SPRING 2007
spell the end of solvent-based products. With this
development, solvent stain manufacturers
switched to a water-based stain.
Spray Specialists began using water-based
stains in 1998, and in time discovered that they
had a life expectancy of only five years at best.
Building owners complained of a ‘leopard spotting’
appearance on the coating.
The major difference between the solvent and
the water-based version was the ability the water
base stain had to breathe or have a higher perme-
ability. Two coats of the solvent applied at 300 sq.
ft. per gallon, per coat, had a perm rating of 6,
while the water based coating applied at the same
rate had a perm rating of 18. The higher the num-
ber the more permeable it is.
If only one coat of the water-based coating was
applied at 300 sq. ft. per gallon, the perm rating
would be 36. Therefore, the higher the perm rating
of the paint, the easier it is for the efflorescence to
pass through (not to be confused with effervescence
which is to show enthusiasm, excitement or liveli-
ness.)
In a low perm-rated coating, a strong drive of
the efflorescence might pop the coating off where
in the higher perm coating it would merely pass
though. What affects the drive? If we have a high
temperature on the interior of the building and a
low temperature on the exterior, the drive will be
greater than if both sides had the same tempera-
ture.
The painting business is in a ‘speed building’
mode. The sooner the job gets completed the bigger
the bonus, and the sooner the owner closes a con-
struction loan, the sooner a tenant gets into the
building. Unfortunately with increased speed of
construction, the building may not have a chance
to dry out before it’s painted.
Let’s talk about concrete!
Concrete is an ideal transmitter of moisture, due to
capillary action. It has a single mission in life — it
always wants the temperature and humidity to be
the same on both sides — no matter where it is.
And will ceaselessly try to achieve its goal.
Have you ever run a dehumidifier in your base-
ment? You know how often it needs to be emptied?
So you have a good idea of how much moisture is
actually coming through the concrete even though
it appears to be dry. An average basement can
transmit several gallons of water through its solid
concrete walls and floor in a 24-hour period.
It is this property that makes it difficult for
paint to adhere and to keep wood floors from warp-
ing. Because of this moisture, mold, mildew and
potentially dangerous toxic fungus are attracted to
“ Concrete is an ideal“ Concrete is an ideal
transmitter of moisture,transmitter of moisture,
due to capillary action.due to capillary action.
It has a single mission in life —It has a single mission in life —
it always wantsit always wants
the temperature and humiditythe temperature and humidity
to be the same on both sides —to be the same on both sides —
no matter where it is.no matter where it is.
And will ceaselessly tryAnd will ceaselessly try
to achieve its goal.to achieve its goal. ““

4. 11SPRING 2007 — SSECONDECOND CCOATOAT
areas where moisture levels are high.
Since moisture travels so readily through con-
crete, the insulation placed in the concrete is not a
vapor barrier. Thus the whole panel is affected on
both sides of the insulation.
The new water-based paints are highly perme-
able. At first it was thought that this factor would
be a plus for water-based products — the fact that
moisture is more readily released than the solvent
counter part.
There is another significant affect that water
has on concrete — efflorescence, the milky sub-
stance that can form on the exterior of a building.
In contrast, a combination of circumstances can
cause efflorescence.
First, a soluble substance must be in the con-
crete. An abundance of calcium hydroxide is al-
ways present in concrete.
Second, moisture must be present to dissolve
these substances.
Third, evaporation or hydrostatic pressure must
cause the solution to move toward the surface.
Fourth, the solution must evaporate to leave
these substances behind as efflorescence. If any
one of these circumstances is eliminated, efflores-
cence will not occur.
How can we stop
the moisture problem?
Spray Specialists has experimented with various
sealers prior to painting. Penetrating sealers are
low viscosity liquids that are capable of penetrat-
ing into concrete surface pores, filling the minor
hairline cracks and voids.
Two types of penetrating sealers include pore
liners and pore blockers. Pore liners ‘line’ the con-
crete pores and enable the concrete surface to be-
come water repellant. Pore blockers penetrate the
pores, reacting with concrete’s consistency. The re-
sulting products are insoluble and hence, block the
concrete pores.
Boiled linseed oil is one of the oldest materials
used to seal concrete surfaces. It is low in cost but
not recommended for sealing wall panels. Silane
sealers penetrate about ½ inch into the concrete
and react chemically with concrete to form a layer
that resists water and chloride penetration. I have
used silane as a pre-sealer but am concerned about
permanency. Silanes are good bond enhancers for
succeeding coats of paint. Siloxane is very similar
to silane although not as effective in reducing
water and chloride penetration. Also, you cannot
paint over siloxane.
A pore blocker I have been using for the last
three years penetrates the concrete up to seven
inches deep and protects the concrete with an in-
ternal hydrogel. When the product is applied, it re-
acts with the free alkali in the concrete.
It permanently anchors itself within the matrix
and will not wash or migrate out. The gel has the
unique property of forming itself in the pores as a
pliable semi-solid that will not expand as do some
liquids at extremely cold temperatures.
This would help to avoid the creation of stresses
that could potentially damage the concrete during
freeze-thaw cycles.
The product also ties up any free reactive alkali
within its gel. [Ask your window glazer how free
alkali can attack aluminum window frames.]
Existing painted buildings have no way to be
pretreated with a water-proofer. The best way to
deal with an existing painted building is to power
wash and then apply two heavy coats of a high
quality 100% acrylic paint. By adding additional
coats of paint, permeability is lowered.
By understanding concrete, efflorescence and
pre-seals, you can provide the building owner with
the knowledge needed to make an informed deci-
sion for a trouble-free, long lasting painted build-
ing that is protected from the problems of
efflorescense.
About the Author
Robert E. Wargaski, president/owner of Spray
Specialists in McHenry, IL since 1972, graduated from
college with a science degree. He worked in research for
the veneer plaster section of U.S. Gypsum. Later
Wargaski served as Quality Supervisor in the
manufacturing of joint compounds and powdered
textures. Wargaski began his own painting business
which specialized in the application of “popcorn” ceiling
textures. In 1974, his firm was contracted to “stain” a
precast wall panel at the Racquetball Club in
Woodstock, IL. Since those early days, Spray Specialists
has stained/painted over 1,000 buildings. Wargaski has
been active in NiPDi and PDCA for several years.