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Foundation waterproofing

James Stufano | Posted in General Questions on

Foundation 10 inch by 8 foot cement walls are about to be poured and I  am looking for thoughts on using a liquid membrane to waterproof the exterior basement walls below grade. I was looking at Polywall where I would seal the cold joint between the footing and wall with a Polywall joint sealer, then roll on the Polywall liquid membrane. The land is on a slope, where we had to blast into the slope for 1/2 of the foundation area. A blend of ledge and soil make up the high side and backyard sides of the foundation and there is around 5 feet of space between the foundation and the sides to work in. The excavator said the soil is nice and dry, but I would expect that this time of year.  I am not sure if I am using the right product for a liquid membrane in the Northeast Zone 5 and what is the best way to protect the membrane before backfilling?  I was thinking of a foam board product like XPS or if Rockwool could be used below grade. I read some had complaints that foam board attracts ants and termites so then I started thinking maybe a dimple layer product. I don’t like the idea of hammering into the cement wall to attach the product. I’ve seen peel and stick membranes where you have to add a primer first, and it seems like a lot of work to roll or spray primer, then peel and stick. I know I’m rambling, but am I going down the right path and suggestions are welcomed. I did not want to add the Arroyo drain board and there will be a Schedule 40 – 4 inch drain, gravel and fabric around the footing. Thanks

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi James.

    I think you are off to a good start. A capillary break between the footing and foundation wall is a necessary and often overlooked aspect of a waterproof foundation. So is a footing drain. Make sure that the footing drain is properly located. This is another detail that is often installed wrong, specifically in the wrong location.

    Beyond these details, how you proceed with waterproofing the foundation depends on your site and your comfort level. You can insulate and protect the membrane with rigid foam, install a dimple mat or other membrane, etc. Here are some articles that should be helpfull:

    https://www.greenbuildingadvisor.com/article/capillary-breaks-above-footings
    https://www.greenbuildingadvisor.com/article/using-a-dimple-mat-to-keep-a-basement-wall-dry
    https://www.greenbuildingadvisor.com/article/how-to-install-a-foundation-drain

  2. Zdesign | | #2

    I used the Delta MS dimple mat on the outside of my foundation along with footing drains, and Dryloc Extreme for a capillary break on the footings. I highly recommend the Delta Dimple mat. It's very easy to install. I used a Ramset for the fasteners but any masonry pneumatic nailer will work quite well. The plastic is very durable and we had no issues during backfill. The only thing I ran into is make sure you unroll the material in the proper direction so you don't have to unroll the whole thing.

  3. James Stufano | | #3

    The Delta MS looks like it comes in 65 foot rolls so I would need 3 to 4 rolls. My quess is to overlap where a new roll starts. Do you put an adhesive or liquid membrane where the two rolls overlap?
    Is it best to still have a liquid roll or spray on product like polywall first even though the Delta MS prevents water from going against the wall, it would seem maybe something like Polywall 2200 joint filler on the top of the membrane and cement wall would close it in. PS - I am not a rep for Polywall - It's what I am looking at. I priced out GCP Bituthene 3000 Waterproofing Membrane last night after my post, and if I get install this with all the drains, glue roll on, etc, I am looking at $6000. I know it important to do it right as it is more expensive to go back, and I agree, just $6000 is a lot and I figure there are other options. Thanks for the links Brian - I will review tonight as they are pouring walls today and have to run.

  4. Zdesign | | #4

    I overlaped the Delta MS a good 6" and installed additional clips/nails every 1' vertical along the seam. The top edge they have a closure strip and tar that goes with it. I tacked the closure strip with tar behind it to start and will go back later and seal the top edge properly when I get a free chance. I have roughly $500 in material for the Delta MS setup which was (2) 8' rolls, a full box of clips which I only used a 1/4 of and maybe $40 worth of ramset nails and charges. I didn't put any additional coatings behind the dimple mat and checked the whole thing over for a rips/tears prior to backfill.

  5. Roger Berry | | #5

    Having faced a somewhat similar setting for my foundation, I would like to add that it is equally important to consider water control for the area inside the foundation. You indicated that you have about half of the foundation blasted into rock. Mine sits entirely on sandstone bedrock, which is somewhat porous and layered. Spring melt that sinks into the soil layer above the bedrock is known to travel along the sandstone surface and lower layers. I have many hundreds of feet of upslope grade that absorbs water and slides it down hill at me. Have you considered whether the rock type and profile will be a potential source of water tracking inside the foundation perimeter.

    While I do have a very robust perimeter drain assembly set beside my footing edge (well below slab height) to grab water from the soil layer, I also protected against pooling water inside the foundation perimeter. The sandstone layering allows water to track under the footings and any wall treatments, so I created a "to daylight" exit point drain at the lowest step down on the footers. I also power washed the entire rock face because I did not want the film of mud left behind to slowly clog the drain line. Overkill maybe.

    All fill used to bring the grade back to level over the irregular rock face was washed stone. This provides three valuable features. Installing "before need" radon pipes was a snap and the rock will allow each pipe to pull over larger areas, the capillary break under the sub-slab foam insulation is provided, and most important, the washed rock will not hold water that weeps out of the sandstone inside my perimeter.

    The contractor doing the foundation work would have used pit run to fill/level most of the depth created by the slope and only a 3" layer of rock to provide a capillary break. Since the pit run would have needed compaction work before the stone layer was added, I asked what the cost difference would be for all washed rock. It was only a few hundred dollars if I recall correctly, since the rock would not need compaction.

    If I had used pit run, many feet of my stepped footings would be sitting in soil that would soak and hold any water tracking through the sandstone. In many places the soil level inside the foundation would be above the footing tops which would defeat any capillary breaks applied in an effort to keep the walls from wicking.

    I am quite sure that I could have faced a soggy pool under my slab. I put in a 4" pipe with cap "witness hole" through the floor slab to monitor conditions. We have had a very wet spring this year and despite my drain to daylight provision, the water level in the low corner did rise to 10" or so. That is still some 15" below the slab foam so I do not see any ill effects. That may also be due to having put Xypex additive in the entire pour, footings and walls. I have been very pleased with the walls performance at not transferring moisture up from the ground or footing despite not having a formal capillary break between them.

    I also placed 3" of (used)XPS on the outside of the foundation and covered that with Grace Bituthene down and over the footings, so perhaps that is a major help. In any case, the basement is quite dry and secure. I do not hesitate to put cardboard boxes directly on the floor and my lumber doesn't warp if placed against the walls. It is a delightfully dry basement compared to the last one I suffered with.

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