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Preparation of Concrete
STRONG BY NATURE • HIGH PERFORMANCE INDUSTRIAL FLOOR COATING SYSTEM
Preparation of Concrete
Coating performance is directly affected by surface
preparation. Integrity and service life will be reduced
signicantly if the surface is improperly prepared. Selection
and implementation of the proper surface preparation
ensures coating adhesion to the substrate and prolongs
the life of the coating system. New concrete must be cured
prior to coating. “Cured” is generally dened as, “concrete
poured and aged at a suitable temperature for at least 28
Examine the Surface
Prior to planning a job the contractor should survey of the
concrete surface. If excessive laitance is present, this material
must be removed down to solid concrete. The coating or
overlay will not bond properly to the weak layer of concrete.
The surface should be checked for barriers such as existing
sealers, curing materials, grease, oil, eforescence, and dirt
that must be removed. In short, you want no surprises.
Test the Concrete
A “water drop” test can be used to determine if the surface
is clean. Water beads on surfaces contaminated with sealers,
curing compounds, oil, and grease. Water beads on surfaces
that are too dense to accept a penetrating primer.
Clean Uncoated Concrete
Remove any chemicals, oil, and grease from the
Repair Surface Defects
Grind or chip off from the concrete surface all projections
greater than 1/16”. Remove any loose concrete, then clean
and ll holes, cracks and other surface defects with an
approved method. Determine if the patch surface texture
should be rough or smooth, and how long the patch needs
to cure before being coated.
Previously Painted Surfaces
Examine the existing coating to ensure that it is well bonded
to the concrete. Any loose coating must be completely
removed. Edges should be sanded to a feathered edge.
Clean the entire oor thoroughly with detergent cleaner. The
surface must be free of all dirt, oils, or other contaminants.
After the oor has completely dried, sand the existing coating
until a powdery residue is evident and all gloss is removed.
Sweep or vacuum clean, and wipe with xylene to ensure
good adhesion of the new system. When coating over existing
coatings, a test patch is always recommended to
evaluate compatibility. Moisture Vapor Transmission (MVT)
Moisture Vapor Transmission (MVT), also referred to as
“hydrostatic pressure”, “capillarity” or “vapor pressure”, is caused by
moisture being present underneath the concrete slab. MVT can cause
blisters, bubbles and other effects in a resinous coating. As moisture
rises, it dissolves salts in the concrete and becomes alkaline. This
alkaline water attacks the resin. Damage caused by MVT does not
constitute product failure. We recommend that contractors include a
written MVT disclaimer in all of their contracts before beginning a job.
We also recommend that contractors always test for signs of MVT
problems. This will not ensure that the problem may never
occur. If a problem is suspected, contact your
FlexRockCoatings™ Representative to discuss preventative
All slabs should be tested for MVT. In slabs that exceed the maximum
test results contact your FlexRockCoatings™ Representative for
Acceptable Test Methods for MVT
Calcium Chloride Test: Perform a quantitative
anhydrous calcium chloride test in accordance with ASTM-
F1869 Standard. The maximum acceptable result for this test
method is 3 pounds per 1,000 sf per 24 hours.
Relative Humidity Test: Perform a quantitative Relative Humidity
test in accordance with ASTM F2170 Standard. The
maximum acceptable result for this test method is 75%.
Concrete Preparation Methods
Once a common practice, acid etching is no longer an
approved method of concrete surface preparation.