Unexplained Damp Spot causing Paint Peeling

9 Jan 2011
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United Kingdom
Hi all, I had these kitchen walls re-skimmed at the end of November and left it a couple of weeks to dry before applying a 50% mist coat of contract matt emulsion in December. All has been fine then a few weeks later I did a base coat of Little Greene Intelligent Matt Emulsion. Roll on about a month later and I noticed there's a spot in the door reveal where the paint and bubbled up. The walls are solid brick and the other side of this wall is a another thick garage wall. There's no real exposure to elements from the other side because of this.

The plaster had thoroughly dried before I did the mist coat, and it was 2 or 3 months before I proceeded with the rest, so plenty of time to breath, etc.



After seeing the damp spot I took my scraper and removed the blistered paint, sanded with some 120 grit mesh ready to paint again. The following day the spot is still a little damp and has lifted further:




Anyone know what's going on here and how I can paint it so that it doesn't lift again? I have some Zinsser Bulls Eye 1-2-3 Primer I can use, but suspect that's not the solution. I can't see where the moisure has come from though:



Inside of the garage, on the other side of the kitchen wall, which is also dry:


Can anyone suggest a way forward? Thanks!
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Can anyone suggest a way forward? Thanks!

In the last photo - what is the large black (white painted) pipe?

My own guess would be a leak in the lean to garage roof, or its flashing. Water is making its way down the cavity and some of it reappearing where your damp spot is.
possibly, but it's a kitchen so there might be a pipe in the wall behind the damp spot, especially if there is a bathroom or cold water tank above.

It looks to small to be water tracking from a leak in the downpipe or soilpipe in the garage.

You could chip off the plaster and have a look.

It would be useful if you put an arrow on the wall in the garage to indicate the spot corresponding to the wet patch.
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As far as I know it's a solid walled detatched house. There is a bathroom directly above, and reason I skimmed and decorated is that about 5 years ago there was a leak upstairs and the kitchen ceiling got ruined. But that was fixed. This damp is a completely isolated spot, not running down the walls from the ceiling. There's also a bit of paint peal you can see that I've rubbed down along the edge of the door frame, but that's not 'wet' as such. I'm guessing drafts through the door gap.

Anyway, here's a picture of the garage, which judging from the picture through the door would make a location where indicated. However this is still about 60cm away from the actual damp spot inside which has a lot of wall to travel down:

Pipe in the wall then. Chip off the plaster and have a look.

Leaking pipe in the wall is what your wet patch looks like.

Might be a nail from the beading in a pipe.

Do you know the route that the water pipe takes, to go up to the bathroom?

And the route the hot pipe takes, to come down to the kitchen?

What about the radiator pipes?
I'm not sure where the pipe runs. There's the cold water stop cock on the right of the door. And on the left of the door is raiator pipe. Here's a couple of pictures before and after romving radiator and skimming the walls:


If I am seeing it properly, that wall certainly looks thick enough to have a cavity. Rather than digging into the plaster to see if there is a pipe, have you a cable and pipe locator (metal detector) you could use? There will obviously be metal on corners of the plaster.
If I am seeing it properly, that wall certainly looks thick enough to have a cavity. Rather than digging into the plaster to see if there is a pipe, have you a cable and pipe locator (metal detector) you could use? There will obviously be metal on corners of the plaster.

No, I don't, but I think I'll have to go and get one.
Here's my take - that bit of the wall has loads of salt in it, possibly from years past with coal fire gases reacting with lime and possibly exacerbated by your leak. The plastering will also have drawn salt out of the wall into the wet plaster. (I have seen this problem in my house). IMHO The damp is now coming out of the air and getting sucked in to the wall by the salts which then grow crystals.

Try this - scrat it back to solid surface and let it dry out as much as possible - heat is good, and fill any dints with 2-part filler. Then paint the whole local area in something like https://www.toolstation.com/ronseal...oxSz03NDIW4ROIxEtJyODcCQfoyd_F74aAl0PEALw_wcB

This seems to prevent the room air getting to the salt, so it can't grow. I seem to be getting on top of a similar problem half way up my chimney breast by doing this.
Thanks, that's very interesting, and sounds no less plausible than the fact that it's a leaking pipe. The only thing is this is a kitchen in a house that has been centrally heated from for at least the last 70 years. Not much coal or smoke. The wall was re-skimmed 3 months ago and completely dried out before I did the mist coat. The only thing is that the weather's been cold and I've had the radiators removed and heating off for a while. It's possible that the cold could have got to the wall, or a draft from through the door frame or key hole. However if that was the case I would want all my paintwork to blister off everytime it gets a bit cold.
You can see the salt crystals growing, so there is def salt there - it doesn't come out the air - it comes out the plaster/brick. The salts are hygroscopic - they attract moisture which then combines with the salts to grow more crystals. As it's near a door, it's also a cold spot, so any condensation is going to increase the moisture in that area, helping salt crystals to grow. You can't get the salt out the wall, but you can stop the water vapour getting to it. That's my theory backed up with what I have seen-done on my own old house.
OK, thanks. So the solution is to dry it out again? What worries me is that as a kitchen there will always be a lot of moisture in the air and combined with the drafty door will be subject to continual condensation and peeling paint. Does that Ronseal Damp Seal really work?

My stairway (along the same wall just above and to the left of this area) is also suffering a similar thing. I put Wallrock Fibreliner on that wall and painted it, but within a couple of weeks it's bubbled up and lifted following hairline cracks in the underlying plaster. I really thought the Fibreliner would contain and conceal, but it looks far worse than before and accentuates the underlying issues. When I prepped the old plasterwork here with filler I'd find that the following day damp salts had just displaced the filler each time. I put a fan heater on it in the end and papered, but it looks hidious now that it's blistered up.

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