A.Carl Hagstrom responds: There are plenty of
ways to detail such a joint. I recommend using a backer rod and
urethane caulk. If possible, it’s best to apply this
after the concrete has had about six months to cure and shrink
back. But this is just a band-aid, not a lasting solution to
the problem. You have to deal with draining the water first.
Then you can worry about sealing the joint to keep out radon
gas, if necessary.
Here in northeastern Pennsylvania we have high seasonal
water tables, so on all foundations we pour, we have to use an
interior perimeter drain to deal with the water. Most builders
think in terms of an exterior drain. But if you have a high
water table, the water will rise inside the foundation. Unless
you have an interior drain, the footings essentially act like a
dam, preventing the water from reaching the exterior drain and
forcing it to rise through the slab.
We typically form and pour our footings and lay drain line
around the inside and outside perimeters (see
illustration, below). The drains must run to daylight or to a
sump pump connected to a storm drain.
Apply a standard asphalt-based foundation coating to the
exterior of the foundation, then backfill with plenty of
gravel. Water is predictable stuff. It will take the path of
least resistance and usually goes just one way — down.
This means if you backfill the outside of the foundation with
enough gravel and provide a daylight drain, the water
shouldn’t rise along the foundation wall and won’t
have enough pressure to leak in through the joint.
Carl Hagstrom, a mason and builder for 20 years, owns
Hagstrom Contracting in Montrose, Pa.