Did you know that 2.4 billion dollars is spent annually on moisture issues in concrete floors?
There has been much discussion about what the acceptable moisture emission (ME) or moisture vapor emission rate (MVER) should be prior to installing a floor finish. ASTM E1907 notes in the appendix that most flooring product manufacturers require a moisture emission rate of less than 3#’s/1000sf in a 24 hour period.
Some manufacturers published requirements can be higher depending on the material, for example, some carpet and resilient floors can tolerate a reading as high as 5#’s. Almost all resinous epoxy floor products fall into the first category.
There are two principal sources of moisture that influence the level of moisture within a concrete sub-floor. For slabs on metal deck, free-water is the principle source of moisture in the concrete. For slabs-on-ground, the initial source of moisture is free-water within the concrete.
All conventional concrete contains water of convenience, or free-water that is necessary to produce a workable mixture. Free-water, as the term implies, is water that is not consumed in the process of cement hydration and remains as nonchemically bound water in the concrete. Time and suitable drying conditions are required to reduce the amount of free-water in a concrete slab to a level acceptable for a flooring installation.
The second major source of moisture in a slab-on-ground is that which originates below the slab. When an effective vapor barrier/retarder material has not been properly installed directly beneath the concrete, moisture vapor from below the slab will migrate upward to, and into the concrete. This natural process of water-vapor diffusion occurs beneath a concrete slab-on-ground regardless of the depth of the water table or presence of a capillary break.
Unfortunately it is prevalent in today’s world to ignore the potential problem created by excess moisture vapor transmission until after the new flooring has been installed and osmotic blistering has already occurred. This can take up to 3-5 months by which time the flooring contractor has more than likely already been paid.
Some flooring contractor’s prefer not to discuss or bring up the subject of potential moisture problems for fear of loosing work. The other reason is that this problem is not that prevalent and chances are you may never have this problem.
But what if you do?
How can this potential problem be prevented?
How can I remedy a floor with high moisture vapor transmission issues beforehand?
One simple method would be to install a topical moisture mitigation system prior to the application of any resinous flooring material.
A topical moisture and pH suppression system is a surface-applied treatment intended to mitigate a high moisture condition within a concrete sub-floor either before or after a flooring problem develops.
What type and how thick a system is needed would be determined by testing. A responsible flooring contractor would routinely test every concrete floor prior to the application of an epoxy coating or resurfacer for high levels of moisture vapor transmission in accordance with ASTM F2170 (Internal Relative Humidity Testing). In the event that the readings exceed 87% they should also perform calcium chloride testing in accordance with ASTM F1869. These tests sometimes require 60 – 72 hours (undisturbed) to provide accurate results.
Quite honestly we strongly recommend that the building owner hire an independent outside testing company to perform these tests prior to going out to bid on any flooring project as the results of these tests determine the cost of the moisture mitigation system to be installed. He can then provide this information to all bidders.
The good news is that some of these systems come with a 10 year warranty against any moisture related issues for the entire installation.
Another good idea would be to avoid doing business with any product manufacturer or applicator that does not discuss the subject at all.
Mike Smedley, Contract Manager