I think it would help a lot of folks here if you would elaborate on this
Here is the scenario!
Concrete is a mineral/salt rich, porous material full of tiny channels and voids.
These pathways are used for migration of fluids and vapors. Migration is due to simple physics - forces working to achieve temperature, humidity, concentration, or pressure (hydrostatic) equilibrium.
Additionally, dissolved metal salts in the migrating water can form relatively large calcium/potassium silicates upon reaching the concrete surface. This ‘swelling' can result in pressure build-ups of 1000 pounds.
That's a lot of pressure for any coating bond to resist.
Added to this situation! Most coatings lose bond strength, or simply will not adhere at all, when applied to a damp, wet, or saturated surface.
Consider the following prior to construction and/or building or prior to installing a new floor system! How dry is my concrete surface? Can it contain more moisture than the coating manufacturer would recommend for optimum adhesion?
Possible solutions!
VAPOR BARRIERS
The pre-construction solution is to use a vapor barrier under the concrete. This vapor barrier is nothing more than a heavy plastic sheet. Use caution not to damage the plastic sheeting or tear it during installation as this will lessen the effect. Older buildings and garages often do not have a vapor barrier.
Sometimes it's easy to tell if you're lacking a much needed vapor barrier. There could be water ( smelly water) under the carpet or rug sitting directly on the concrete. If the surface is painted, there might be water filled blisters in the paint.If the concrete is not covered, it could be covered with tiny crystals, the result of mineral salts being left behind by the migrating moisture.
One way to test the exposed concrete for moisture migration is to tape a sheet of plastic (several square feet in area) to the floor and see if water condenses under the plastic. however, moisture migration might occur only after rainstorms, spring thaws and etc..
SOLUTIONS FOR A VAPOR BARRIERLESS FLOOR
There are lots of partial solutions, but no ‘sure thing' short of pouring new concrete over a new vapor barrier.
A ‘Breathable' floor system is one common solution. These "systems lets the moisture pass through the floor coating and very little impact on coating interference. There are a growing number of porous, coatings, and other products on the market. For garages/warehouses and ect we currently use GP 3460 epoxy primer and GP 4409 polyurethane clear top coats for areas in which we feel moisture is a concern. This is the installation I personally prefer but there are other ways to go.
Next are sealers that soak into the concrete and form crystals within the voids and channels inside the surface of the concrete. This reduces permeability and porosity of the concrete, generally restricting the flow of fluids, but not vapors. This treatment is easy and quick and just might ‘densify' the concrete enough to solve, or greatly reduce, the moisture problem and assist in the bonding of "regular epoxy" which would normally fail, by lessening the amount of mineral salts, etc. that can migrate to the concrete surface causing - coating interface. "pre-primer"
Finally, there are floor epoxies that can bond to wet or damp surfaces directly and resist the pressures (over 1000 pounds) that can build up on the surface of the concrete to minimize coating interface. By sealing the concrete surface, moisture, concentration, and pressure equilibriums would be reached inside the concrete which stop the flow or movement of moisture,
although not its presence.
Bond adhesion, however, is influenced by more than just moisture levels. A good, strong bond
requires careful surface preparation. The surface must be clean, dust free, solid (not deteriorating), and have a good profile (microscopic peaks and valleys) to maximum surface contact. However the presence of pre-existing coatings, sealers or grease/oil spills could preclude a good bond.
Finally, Moisture and salts
can and do migrate through concrete slabs as they seek equilibrium with the environment above the concrete. The resulting pressures and condensing water vapor can ruin a coated floor.
After-the-fact solutions include using a breathable surface coating, reducing the porosity and permeability of the concrete and/or using epoxies that can bond sufficiently well to moisture rich concrete.
Hope this helps!
