Replies

1. Expert Member
   Michael Maines | Sep 28, 2019 10:30am | #1

   Paxson, there are a variety of things to consider, but they come down to: how well does your site and backfill drain, and how waterproof does your foundation need to be.

   If you have good drainage, use freely draining backfill, sleeved (and, ideally, redundant) drain tile, capillary breaks, impermeable interior insulation and the above-grade concrete can dry to the exterior, plain old bituminous dampproofing should be enough. If you are unsure about any of those factors you can add a dimple mat and/or use an elastomeric coating. I don't know specific numbers to look for; 8 feet of water column exerts 3.5 psi, but if you're trying to keep all moisture out of the wall then water vapor is also a concern.

   Generally speaking I would trust the spray-on coatings that require a license to install more than something a homeowner can buy and roll on themselves. I've used Rub-R-Wall and Tremco Tough-N-Dri and have not heard of resulting problems, but your mileage may vary.

1. 
   Jon_R | Sep 28, 2019 01:09pm | #2

   Add "sloped, water blocking near surface layer extending well beyond the fill" to the list. My guess is that this makes far more difference than what wall waterproofing you use.

2. 
   paxsonalaska | Oct 02, 2019 02:07am | #3

   Thanks for the reply. To follow up here, I've decided to go with Ames Bluemax, a water-based elastomeric coating that can be rolled or brushed onto the foundation. It was available on Amazon and at a local Ace Hardware at about $200 per 5-gallon container. The total material cost was about $1200. Even though the drainage in my location is very good already (I'm on a moraine of glacial rock and gravel in Alaska), I consider that a small price to pay for a big increase in reliability over conventional asphalt-based coatings.

   Went up to the jobsite and talked to the guys grouting the foundation today--they told me they've repaired plenty of foundations with dampproofing, but never one with elastomeric rubber coating. That pretty much justifies it for me.

2. Expert Member
   Peter Engle | Oct 02, 2019 08:17am | #4

   Make sure your backfill does not contain big rocks. Anything smaller than 3"-4" is probably OK. Bigger rocks can scrape the waterproofing off as they settle. Worst case, big rocks can put enough point load on the foundation to cause damage.

1. 
   paxsonalaska | Oct 02, 2019 12:05pm | #5

   Thanks. The waterproofing layer will be protected by 4 inches of foam insulation everywhere but the footings. Great point about the rocks. I'll take another look at the backfill today but it's basically just sandy gravel, and the biggest rocks are probably 2 or 3 inches across.