- Bad structural design. Insufficient rebar quantity or improper rebar placement can result in wall cracking.
In my opinion, the best method of ensuring a waterproof wall is to use a subsurface drain system on the outside of the wall. This intercepts groundwater before it hits the wall. Either drain rock backfill or a proprietary fabric-polyethylene sheet system works well. In each case, a perforated drain pipe must be installed at the bottom of the footing to collect and transport groundwater away.
Membrane systems adhering to the outside of the wall can also work well, as long as they’re applied correctly and no damage occurs to them during construction — a tall order, generally.
Waterproofing admixtures are great; however, because concrete is by itself waterproof, they tend to be redundant. Also, improper design or construction (see above bullet points) can trump any benefits this system might provide.
I was once involved as an expert witness in a leaking basement wall case. The house was situated on a clayey hillside — an indicator that migrating groundwater would be likely. The walls were built in the winter; rain had transformed the excavation into a muck pit. It was obvious the contractor was in a hurry. He did many things wrong, but here are the ones that caused leakage:
- He did not mechanically vibrate the concrete, leaving voids and rock pocket conduits for groundwater to get through.
- His perforated pipe drain system was installed in the slop of his excavation, causing it to foul and plug.
- Rather than backfilling with washed drain rock, he used a sand-gravel mix, which in the mucky conditions was not porous enough to ensure groundwater would go down rather than sideways.
- His stick-on membrane was punctured and was not properly overlapped.
In short, this contractor was begging for the lawsuit and judicial spanking he ultimately got. Even the best expert witness could not bail him out!
Tim K. Garrison, P.E., M.S.C.E., of ConstructionCalc.com has authored a book and several short courses and lectures on topics relevant to builders. He can be reached by e-mail.
The views expressed in this article represent the personal views, statements and opinions of the author and do not necessarily represent the views, statements, opinions or policies of the National Association of Home Builders. NAHB does not necessarily endorse any of the views expressed by the author and NAHB is not responsible for any direct or indirect consequences arising out of the views expressed in this article.
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