LESLIE: Now we’ve got John in Missouri on the line. John, what’s going on?
JOHN: Well, I live in an old house built in 1892 and it has plastered walls. And I’ve got a – I had a leak this spring. I had a gutter overflow and it got behind some flashing and created what I call "plaster cancer," which is this sort of crystalline stuff that grows out of the plaster.
JOHN: I mean it didn’t make the whole thing fall down. It just is crystal. And I got the leak fixed and I tried – I scraped all that stuff off and put a sealer on it – quick sealer paint – one of those alcohol-based things.
JOHN: And the cancer keeps going. Now it’s blown that paint off. It’s not as much but it tends to continue. And I wondered if there was something you can do to stop that from happening short of tearing that whole plaster down.
TOM: So the plaster, when it gets wet, there are sort of fingers, so to speak, that wrap around the lath behind it. And when it gets wet, it loosens up.
JOHN: This plaster is actually on brick.
TOM: Oh, it’s on brick? OK. Alright. Strike that. So what else could be happening is if it’s on brick and the brick got wet – the bricks are very hydroscopic, so you could be continually pulling more moisture through there. Are you absolutely certain that you’ve addressed the leak completely? Because it doesn’t sound that way. It sounds like you’ve still got some moisture in there.
JOHN: There could still be some moisture in the brick, I suppose, but it’s been super dry here in St. Louis since the end of July. And this – I got the thing fixed about the middle of July: all the flashing on the – it’s on a bay window. All the flashing above that was redone and – but it hasn’t rained pretty much at all since then.
TOM: How big is the patched area?
JOHN: It’s, oh, I don’t know, maybe 10 square feet. It’s not huge.
TOM: And that whole area is breaking up and forming these crystals?
JOHN: Yeah. Well, it’s doing this crystal-growth thing, which blows off whatever paint you put on the surface on it.
TOM: I wonder if part of what you’re seeing is the paint basically disconnecting or delaminating from the plaster itself.
JOHN: Well, yeah. This cancer sort of grows below the paint. But it’s – my problem is it’s dried up now. It hasn’t rained, so it couldn’t possibly leak; it hasn’t rained. And also, the thing is repaired.
TOM: What I would do here is this: is I would try to strip out all the paint that I could and I would probably use a paint stripper to get whatever is left behind. Maybe a gel-based stripper. And then I would put another skim coat of plaster over it. Let it dry really, really well. And then I would prime it with an oil-based paint and then repaint it.
But I think the plaster is basically disintegrated, in some respects, and I think you’re going to have to do some partial rebuilding of that surface.
JOHN: Yeah. OK. Well, because it’s – yeah, the plaster is this two-layer plaster. It’s got kind of a – looks like cement at the base layer and then it’s got a real fine, white layer that’s the finish layer. So just reapply that, huh?
TOM: That’s right. After you get rid of any loose material that’s there. You really want to make sure you have a solid base and then you can put a new skim coat on it.
JOHN: OK. Alright. I’ll give that a try.
TOM: Alright. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.