We've recently had exterior waterproofing applied our house. In the process, we removed an old cold room that was underneath our porch. They walled up the entrance to the old cold room, and then removed the walls and floors.

While they were removing the old cold room, they noted that the concrete block walls of that cold room were filled partially with water. We haven't been exposed to heavy rain in the last few months really.

The interior of our unfinished basement concrete block foundation walls were painted with something black many years ago, probably as a waterproofing measure. So now, we have really good waterproofing outside, and some crappy waterproofing inside.

The trouble is, I'm convinced that if there was water in the concrete blocks of the old porch, that its likely that many other spots in the house have water in the foundation. Lots of it.

Is there a good way to find out, and possibly drain this water out? Will a dehumidifier work in this situation?


Should we try to remove the black substance painted on to the inside of the concrete block, to help dry out the walls from the inside now that we have exterior waterproofing? if so, how?

  • 1
    I question your conviction. Water would easily get into concrete blocks from above, sure - and rain on your porch, presuming it leaks (many porches do, mine does) would penetrate the blocks filing the cavity. It won't, however, easily spread to neighboring blocks - thats why it's still in the blocks you found, it doesn't move through concrete easily. Yes, water wicks through it - but not enough to fill its neighbors. Nov 6, 2011 at 0:16

1 Answer 1


Is there a good way to find out, and possibly drain this water out?

A drill with a concrete bit should do the trick.

Will a dehumidifier work in this situation?

A basement in most climates (any place with somewhat humid summers) should likely have a dehumidifier regardless. So it definitely won't hurt.

  • will drilling partway through the foundation like that cause problems?
    – Kyle
    Nov 6, 2011 at 1:01
  • it shouldn't cause any problems. If you don't like the hole afterwords, you can patch it up with hydraulic cement.
    – DA01
    Nov 6, 2011 at 1:45

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