Dampproofing and waterproofing

Concrete Construction, Oct, 2004

Q. I am building a new home with the help of a builder. I like to have my foundation sprayed with a dampproofing sealant and wrapped with a polyethylene, dimpled wrap. The house is being built where there is a high water table and high clay soil. The builder tells me that the spray is not necessary with the wrap, but I would like both (weeping tile is standard). My research tells me that the wrap does not protect the concrete from moisture, but the sealant will. The wrap protects from hydrostatic pressure, whereas the sealant does not. So I concluded to have both is best. What is your opinion?

A. The short answer is you're on the right track. The basic problem is that water vapor and liquid water behave differently. Also, the type of product that best stops water vapor is not necessarily effective against liquid water, and the products that stop liquid water won't entirely prevent the passage of water vapor. Particularly with your concerns about the soil conditions, a "belt and suspenders" approach may be just the thing on this project.

Because you're doing something additional (rather than omitting something), and because it's your money, you should be able to call the shots on this one. And it's much easier to do it during initial construction and avoid a problem than to come back later and correct it. The other consideration, of course, is that not all products perform equally well. That might be something to investigate further and work on with your builder.