Sealing, Painting and Insulating a Crawlspace

February 25th 2006
Sealing, Painting and Insulating a Crawlspace

Q:  I have a question about sealing, painting and insulating a crawlspace. We have purchased a 17-year old townhouse. The building inspector we hired made us aware of some minor dampness emanating from the concrete floor and foundation walls in the crawlspace. There was some dampness on the crawlspace walls and floor and a musty odor. There has not been any pooling of water. Fortunately the inspector found no wood rot in the floor sills or joists above the concrete. We also intend to use the crawlspace for storage. We were advised to seal and insulate the interior crawlspace walls. I would also like to paint the floor with Alkyd paint to facilitate periodic cleaning of the crawlspace floor. A paint store employee told us to first etch the concrete with Muriatic Acid before priming and painting. Is this really necessary? I have previously painted concrete floors and porches with good results without using Muriatic Acid.

I would also like to know the best method to seal the walls. I have heard about two methods, one is to glue poly sheets to the walls and the other is to apply a liquid sealer. Which would you recommend?

We planned on attaching Styrofoam insulation to the walls. Can this be applied to the poly sheet?

Should we also insulate below the sub floor? Again I have heard about different methods involving foil sheeting, Styrofoam and fiberglass. Which is best for this application?



Dear Ken,

A:  Crawlspaces become a forgotten area in many homes, as they are normally dark and smelly.

Here is what to do:

1.  Consider installing a Humidex crawl space ventilation device to control odours and high humidity levels. You can find out more about the Humidex products and the location of a dealer near you by visiting their website at or by calling their toll free number at 1-800-416-9111 (home owners in B.C. or Alberta should call: 1-888-215-9023)

2.  Wash the entire area using the Shell Busey Home cleaning formula, rinse well and allow it to dry.

3.  Apply Aqua Seal concrete sealer (Available from Cloverdale Paint and Windsor Plywood Stores) to entire floor and concrete walls. Apply by puddling it out onto the floor allowing it to really seep into the concrete and rolling with a heavy nap roller, allow it to dry.

4.  Apply 1 1/2" inch rigid foam insulation to all walls from the underside of the floor joists 24 inches below outside ground grade level, this has an adhesive for this application to make the job nice and easy.

5.  Insulate using batt insulation and vapour barrier between joists over top of concrete foundation wall and seal with acoustical caulking. Roxul Insulation is an excellent choice for this area, available at all Building Supply Centers.

6.  Apply Reflectix foil insulation to the underside of floor joists Staple to the floor joists and where ever there is a seam, be sure to tape it with the recommended tape for the Reflectix product.

It's Just That Easy!