As I mentioned in my last post, cement-based products like concrete and grout are naturally porous and water passes through them easily. Liquid water in soil can exert a huge amount of hydrostatic pressure, forcing water into the porous foundation wall. And because water vapor always tries to reach equilibrium, it will try to diffuse from moist soil (which is typically at or near 100% humidity) through the wall and into the relatively drier basement air. Water moving through basement walls can create frost problems, encourage mold and mildew growth, and ruin interior finishing. The first line of defense against water intrusion is to create a mechanical barrier on the exterior side of the foundation wall.
Traditionally, builders have “waterproofed” foundation walls with a black tar or asphalt-based spray. This solution meets code and it’s affordable, but it suffers from an ironic flaw: these coatings aren’t actually waterproof. In fact, because they still allow some water to pass through them, they can only be called “dampproofing.” Dampproofing products are also prone to becoming brittle and cracking over time. A second option is to use a peel-and-stick waterproofing membrane. Peel-and-stick membranes work very well but are expensive, harder to find in Alaska, and work better on smooth concrete walls without many irregular shapes. A third option is to use a liquid elastomeric rubber product. These products are more expensive than dampproofing and require multiple coats, but they are fully waterproof, very flexible, and stable as long as they’re protected from UV exposure.
For my foundation I used Ames Bluemax elastomeric rubber coating. I’m a fan: it was easy to apply and dried quickly to a funky, sparkly dark blue. I called Ames several times to ask for advice and they were always responsive and helpful. My only reservation is that because it’s water-based, Bluemax needs to be applied at warmer temperatures to dry and cure properly. Falling temps and rain caused some concern, and if it were even a few degrees colder I think peel-and-stick would have been a better option.
Photos taken October 7, 2019. Posted November 15, 2019.
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Thinking of doing this myself, any tips?
Go for it! Foundation waterproofing is not difficult at all, it just takes time (and willingness to buy a decent product). I had a good experience with Ames Bluemax. If you’re in Alaska, I’d definitely recommend doing this soon, before nighttime temperatures have a chance to dip below freezing. Freezing temps can cause water-based products to develop ice crystals, which compromises their effectiveness.
How about insulating the outside of your cinder blocks if they are below grade? currently The inside and outside of the crawl space is insulated with spray foam. If its insulated on the inside is it still important to insulate the outside?
The outside of my foundation wall is insulated with 5″ of XPS foam (one 2″ layer and one 3″). The layers are all glued and the seams are taped, and the foam is glued to the wall. I believe that assembly should have an R value of about 25, which is far more than most people do in Alaska.
It’s possible to have a block wall either inside your building’s thermal envelope or outside of it. I chose to keep it inside mostly to prevent heat loss from the in-slab hydronic heat. It should also help more heat reach the footings and keep them frost-free.