How do you reduce vapor transmission
Installation of a concrete vapor barrier coating is the best way to control moisture vapor transmission. Most floor covering manufacturers and the ASTM state the maximum allowable moisture vapor emission rate is 4lb/24hr/1000sf for successful flooring installations. The moisture emission rate can be determined through a Calcium Chloride Test. Anything greater and remedial action is recommended to reduce the rate of vapor transmission before flooring installations. Vapor barrier coatings are able to control moisture emission rates up to 20lb/24hr/1000sf.
Calcium chloride test
In order to determine the moisture vapor emission rate of your concrete perform a calcium chloride test. To perform the test, a small amount of calcium chloride (salt) is placed under plastic on a clean piece of concrete. The calcium chloride (salt) absorbs the moisture coming from the concrete slab over a period of about 72 hours. The weight gain of the calcium chloride is then measured and the moisture vapor emission rate MVER is calculated. If a high amount of moisture is present in the concrete (over 3 lb according to a calcium chloride test) it is best to use a moisture vapor barrier coating.