Choosing a Vapor Barrier
- Bottom line: If you want to make sure your slab on ground gets dry and stays dry, use a vapor barrier.
- Cure with waterproof sheets rather than with water or curing compounds.
- All vapor barriers should conform to ASTM E-1745; but consider going with a barrier that has water vapor permeance less than 0.3 perms.
- A 10-mil barrier is probably OK for residential construction if you're careful not to puncture it during construction.
- If laser screeds or heavy placing equipment will be on the barrier, go with 15 mils.
- Starting with lower water-cement ratio concrete will let the slab dry faster. Keep w/c at or below 0.5.
- Vapor barriers also block gases, such as methane or radon. Radon is the second leading cause of lung cancer in the U.S., according to the American Lung Association.
- Typical 8-mil polyethylene sheeting costs 5 to 7 cents per square foot. A 15-mil vapor barrier can be about 25 cents per square foot. Sure, that's an increase, but it's better than a damp, discolored slab.
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