"A typical industry standard is between 3 and 4 pounds per 1,000 square feet. Anything that exceeds that you need to deal with appropriately," Anderson says. "If you're anything above that consult the material manufacturer to find out the best way to handle it." Anderson usually recommends a vapor barrier or vapor dissipating epoxy underneath the overlay.
Contractors also need to test how much moisture is in the concrete. This can be done using either a calcium chloride test or a probe in the concrete, Reynolds says. While the calcium chloride test has been used for moisture testing for years, the newer probe test will measure deeper into the concrete. "There are arguments for both the calcium test and the probe. My feeling is you can never be too safe, and doing both certainly wouldn't hurt. And refer back to the manufacturer's recommendations or specifications as to the maximum amount of what moisture vapor transmission should be for their product to work," Reynolds says.
Rules to live by
Every job is different, and the required surface preparation will vary just as much. If you want to avoid overlay problems and call backs, here are some surface prep rules to live by. Do not cut corners. Do not rush. Do the surface prep how it should be done. Be obsessive. A thorough, complete surface preparation process is the best start to a trouble free adhesion.
And when in doubt, call someone who knows more, Lowe adds. Always ask for help before moving on. Talk to the overlay material manufacturer and find out what surface prep they recommend.