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| MOISTURE VAPOR EMISSION MYTHS |
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- Hydrostatic pressure causes failure.
Simply defined, hydrostatic pressure is the pressure or force exerted by water upon a below grade concrete surface. The body of water (the ground water in this case) MUST be higher than the concrete slab. It (hydrostatic pressure) cannot be applicable to a slab on grade.
- Vapor pressure can build up, causing flooring failures.
Not true, though alkaline salts can accumulate beneath a concrete surface and actually contribute to erosion of the concrete and breakdown of the adhesive.
- Osmotic pressure is the cause.
Osmotic pressure does not affect adhesive bonded floorcovering systems. It can sometimes occur with epoxy or urethane poured flooring.
- Latex based adhesives are more moisture-sensitive than the older solvent-based adhesives.
Latex based adhesives, though somewhat less moisture resistant than solvent based adhesives, are definitely more susceptible to alkaline attack.
- Moisture vapor can't occur in a 30-year old concrete slab.
Depending on the vapor barrier in place, the structure of the concrete, the design of the base materials and the placement of the concrete, older, pre-existing concrete can often times emit high levels of moisture emissions.
- Water vapor moves from colder to warmer.
The opposite is in fact true.
- Moisture induced flooring failures can't happen on a suspended slab.
Quite the contrary, some of the industry's greatest problems occur in slabs above grade with a non-perforated steel pan construction. The water of convenience in the concrete mix has no place to escape, and is contained by a curing/sealing compound applied to the surface. The water of convenience is released via the action of the flooring contractor troweling the adhesive on the concrete. The escaping moisture can and will affect the adhesive bond line.
- Once the building is acclimated, the "moisture problem" will go away.
As a building is acclimated and brought under HVAC control, the moisture vapor emission levels will actually increase. This is a fundamental nature of concrete and pressure and the relationship between temperature and humidity within the building. Without acclimation of the interior space, a building's concrete slab will not exhibit any moisture vapor emission transmission. The space must be acclimated under HVAC control and then the concrete can be tested for moisture emissions. With a properly placed vapor barrier in place, moisture emissions through the concrete will reduce with time.
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