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Concrete Slab waterproofing

jonrossen's picture

OK, first off, what I'm asking about is a 'hack' fo keep water from seeping up into an old concrete basement slab.  I realize this is more than likely the result of pouring the slab incorrectly in the first place.  The slab was installed a long long time ago and I'm not interested in re-doing it. So there is no need for a discussion of proper slab on grade techniques at this point...

The house (> 100 years old)  has an excellent perimeter foundation drainage system. (Installed with the new foundation 7 years ago)  Underneath the house has been bone dry and no moisture seems to be getting underneath from outside the footprint of the house.

The exception to this is a concrete slab in a basement that is about 30% of the footprint of the house.  It is well inside the perimeter of the house. It is accessed via a set of exterior concrete steps hidden behind two cellar doors right off the driveway.  The basement area is separated from the crawlspace by retaining walls that go around it's entire perimeter.  There is no signs of moisture coming in from the surrounding retaining walls; as I stated earlier the perimeter drainage has been 100% efficient.

After a period of heavy rain a small part of the concrete floor is wet.  I'm assuming it's the result of ground water pressure coming up from directly underneath.  It's really not much of a problem but would like to see if I can fix it; we do have a sump + pump if the water total after a wet winter gets to be too much.  I'm not interested in replacing the slab and would like a decent 'band-aid' approach if possible.

Does anyone know of a fairly reliable concrete waterproofing material that I can apply to the surface of the slab in the problem areas?

thx for any tips!  jonR

I doubt that waterproofing (post #214540, reply #2 of 2)

I doubt that waterproofing would be very effective -- water would force its way up along the edges and through any cracks, regardless.

Your best bet is probably to trench the concrete and install tile, draining into your sump.

You might, however, try simply boring holes near the bottom of the sump.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville