Stopping dribbles of rusty coffee coming through concrete wall

August 1, 2012 3:46 PM

We have tiny but ugly drops of rusty coffee coloured water seeping through our toilet wall. The toilet is a tiny U shaped room with water coming through the two walls that are external. The thick layers of existing paint were holding it back but gradually peeling up in a few places. I hacked back the old paint and put on three layers of oil-based concrete sealant paint but the seepage is coming through that like it's not even there. What's the next step? I'm not sure that stopping the water coming is an option, since the walls are structural and thick concrete.
posted by Sebmojo to home & garden (11 answers total)

Water is the universal solvent. If it's there, it will get through eventually. If you don't figure out where the water is coming from, you could run the risk over major structural damage in the future. The best way to keep water out is to have it not be there.
posted by The Light Fantastic at 3:58 PM on August 1, 2012

You need to figure out where the water is coming from and fix it pronto. And by fix, I mean at the source, not trying to seal it into your walls with paint. Else it could turn into a Very Bad (and expensive) Thing (if it hasn't already).
posted by violetk at 4:11 PM on August 1, 2012 [1 favorite]

Based on the little information here, it appears that whatever waterproofing there used to be on the exterior of this wall has failed. You need to repair/replace the waterproofing at the outside of this wall before the water gets into the wall, not on the interior surface after it has already come through the wall. Because of how you have described it, I suspect these walls are below-grade? And what you are seeing is hydrostatic pressure forcing water through the wall.

A temporary measure that may help is also to go outside and confirm that any rainwater/gutters/etc. are not all of a sudden discharging water right against the wall (run the rain leaders out 6 feet+ from the face of the building before allowing them to discharge)
posted by misterbrandt at 4:25 PM on August 1, 2012 [1 favorite]

Is this your house? Can you give us pictures? Please?
posted by TomMelee at 4:42 PM on August 1, 2012

I'll post some photos tonight, I'm at work at the moment.

The building is a 3 story 1940s concrete apartment block, we own one of the six apartments (the middle floor).

The external stairs wind past the external wall that's on the other side of the leaking wall. The stairs and that external wall are covered by a roof that's in very good condition and recently had a new membrane applied.

Because it's covered by the roof, the outside portion of the external wall that's leaking never gets wet from rain. The paint on the outside is also in perfect condition.

I guess there could be a leaking pipe inside the wall upstairs?
posted by Sebmojo at 5:33 PM on August 1, 2012

The stairs and that external wall [that's opposite the leak] are covered by a roof that's in very good condition and recently had a new membrane applied.

Are you saying that the leaking walls are not covered by any roof, or not by a roof that was recently repaired? The leak could be from the apartment above, or from the roof. Does it correspond with rainfall?
posted by slidell at 6:19 PM on August 1, 2012

The leaking walls are covered by a roof. The leaking doesn't coincide with rainfall, AFAICT.
posted by Sebmojo at 6:57 PM on August 1, 2012

Might be worth eyeballing the sewer vent in the roof; if the flashing is loose around it, water could travel down the outside of the pipe and into the wall space.
posted by jenkinsEar at 7:57 PM on August 1, 2012

Huh. Yes, that's a good point. I'll have a look when I get home.
posted by Sebmojo at 8:37 PM on August 1, 2012

It might be worth checking to see whether this newly-installed roof membrane is ducting water into the wall somehow. I've lost track of the number of times someone I know has discovered water coming into their house due to flashing being installed backwards or things like that.
posted by hattifattener at 11:35 PM on August 1, 2012

You said you renewed the paint -- I'd say it's not coming through the paint.

You have a leak in the roof or in the wall, and it's seeping down and out. And it's going to be difficult to trace, because if it's a pipe and you turn the mains off, you'll still get seepage for... days, maybe.

Does it lag rainfall? Begin leaking say two days after the rain? Or does it leak year-round? That could help you figure out whether it's a pipe... Or it could be a drain... try to correlate with when the people above you take a shower or run a bath or whatever. I'd guess their bathroom is directly above your bathroom.
posted by wrm at 6:35 AM on August 3, 2012