Localised crumbling on an interior wall with no internal pipes -
September 28, 2021 2:05 AM   Subscribe

An interior wall has a few spots where the paint has come away and the underneath is crumbling (see images on Imgur). The wall doesn't have any pipework or anything behind it. Feels dry to the touch and there's no water damage visible anywhere around the wall. Is this a localised issue that I can sand, polyfil and repaint? Or is something more disturbing afoot? The building is an ex-local authority maisonette, built in the 70s.
posted by Cantdosleepy to Home & Garden (6 answers total)
Best answer: Looks to me like efflorescence, either from rising damp or perhaps due to the cumulative effect of repeated slight dampenings from leaf spraying or transpiration from that rather magnificent houseplant.

If it's from rising damp I'd expect to see some sign of it manifesting on the other side of that wall as well.
posted by flabdablet at 2:24 AM on September 28, 2021 [1 favorite]

Response by poster: Thanks! The other side of the wall is dry and undamaged.

So could I scrub and sand, then prime and paint the area, or will it require some kind of more involved process?
posted by Cantdosleepy at 3:46 AM on September 28, 2021

I'd guess your proposed solution will work just fine, although if the source is dampness from the houseplant, you may have to figure out what you need to change about that in order to prevent it happening again.
posted by restless_nomad at 4:44 AM on September 28, 2021

Best answer: If that was my wall, I'd hit it with an orbital sander loaded with very rough (40 grit) paper until I'd got all the crumbly bits out, then dampen it slightly with a spray bottle, then apply filler in coats no more than say 4mm thick, allowing it at least a day to set up between coats, until the filler stood slightly proud of the rest of the surface; then I'd sand it back to level using a steel straightedge to check, then prime with a water-resisting primer/sealer/undercoat, then topcoat.

In a few years that would tell me for sure whether the issue was surface dampening from houseplant or houseplant care, or whether it was rising damp; in the latter case I'd expect to see crumbling around but not inside the repaired zone as damp from behind the waterproof undercoat made its way out to the edges.
posted by flabdablet at 5:29 AM on September 28, 2021 [2 favorites]

Best answer: I'd agree with the other posters that it appears to be efflorescence, and unlikely to be houseplant related unless that plant had been positioned right in front of where this is happening. I think your proposed course of action seems fine. If it solves the issue completely great, if the issue reoccurs in a year or three you will have learned that it requires some more serious remediation of some sort, which you can do then. If there are no pipes or anything likely to cause condensation inside the wall, I'd guess your odds of this never happening again are pretty good.
posted by lhputtgrass at 1:59 PM on September 28, 2021 [1 favorite]

unlikely to be houseplant related unless that plant had been positioned right in front of where this is happening

Yeah, when I floated that possibility I was assuming that the plant had been moved aside in order to take the photos; the effect on the wall does seem to be at about the same height as some of that plant's leaves.
posted by flabdablet at 11:35 AM on September 29, 2021

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