Backup waterproofing for waterproof concrete walls
I’m considering using a crystalline waterproofing admixture* in my foundation walls. Would you install backup waterproofing for this? Small cracking is self healing, but it seems like larger cracks in the concrete could lead to waterproofing failure. I’m planning a finished basement, with interior rigid foam, so the concrete won’t be readily accessible for repair. (Rochester, NY area)
–John
*For those not familiar, these are concrete admixtures that react with water and calcium to form crystals in the capillaries in the concrete. The crystals block the flow of water through the concrete. When small cracks form, water entering the cracks causes new crystal growth, sealing the cracks and healing the waterproofing. KIM and Xypex are well know brands.
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The best waterproofing for basements is a good drainage system. Place the white PVC drainage pipes even with the bottom of the footings in a bed of washed stone, cover with washed stone and filter fabric to keep the sand out of the drains, then backfill with good drainage material - clean sand or gravel with no large stones which can damage a green foundation. Near the top of the wall install a finish of washed stone. Run the drainage ditch to daylight.
Skimping on drainage details is a losing proposition no matter what materials you use.
John,
I'm assuming this is in addition to the perimeter drains that Bob writes about, but as a substitute for the exterior damp-proofing?
i've had very good results using Xypex, but I guess it depends on how large cracks you anticipate in your walls. It can seal small ones (to 4mm I think?). Xypex has other products that work on larger ones or holes, but that's after the fact. For all the work that's involved, I'd still be tempted to use a more elastometric product on the exterior as a belt and suspenders approach. That said, I wouldn't lose any sleep just relying on the Xypex admixture.
I'm planning a full system with proper grading, washed stone, perforated pipes, geotextile fabric, a sump if needed, etc. I'll insist on good quality concrete and proper control joints. I'm just wondering if the xypex needs additional exterior damp-proofing. It's self healing for cracks up to 0.4mm (1/64").
John,
No. it's an either/or choice. The only reason I suggested using damp-proofing too was that it is so cheap and quick to install. The Xypex is a permanent, reliable solution.