Retrofit addition of footing at foundation base; capillary break?
We’re finally addressing our wet gravel-floored utilities basement – we’re putting in a slab floor. In digging down around the inside of the foundation wall to lower the floor and make room for the slab etc., we discovered that there is no footing under the formed concrete foundation wall! (This wood-frame house was built in 1936, has 2 stories above the basement, and is in Maine, zone 4-5). Argh. The wall sits on hard dense clay. And guess what? Water trickles in underneath. Contractor suggests forming a footing to the inside of the existing wall. This footing would sit above and below the bottom edge of the wall, and have a small (2″ or so) lip under it. Imagine a fat lower-case “h” shape. We’re drilling into that wall 6″ deep, along a line about 3″ above the bottom, every 2′, to insert 6″ of a 12″ long, 1/2″ rebar, the other end of which will be incorporated into the new concrete footing.
If this is a bad idea for a solution for the missing footing, please tell me!!
Now, about the capillary break. I know there’s supposed to be a capillary break between the footing and the concrete foundation wall. That would be, say, a layer of 6mil plastic, or TenoArm, or Tu-Tuf#4, right? However, the usual scenario is that the foundation wall sits square on top of that nice slippery layer. But how about in this scenario, where the footing is kinda on the side? The capillary break layer would surely cancel any holding power of the concrete. But maybe the puny 1/2″ rebar is enough, and the perceived adhesion between the new and old concrete wouldn’t deal with the shear anyway, so just count on the rebar and the 2″ lip, and install the plastic capillary break? Man, I’m not very confident about all this…
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