Strange circles/ stains appearing in plaster (NOT damp tho)

[SeaSpirit]

Hi All,
I've got a really strange problem and was wondering if anyone knew the answer. About 2 years ago I began a full conversion of a house into two flats. I'm fairly competent at most DIY and did everything (bar gas and electrics) myself. Obviously it takes much longer this way, but I was on a really tight budget. Anyway I skimmed over an existing wall approx. 20 months ago and fitted a kitchen in the room. About 6 months ago, a few random circles appeared in the wall, where the paint (which had been pva sealed) flaked off in a really fine dust. The circles varied in size (typically about 4inches across) and were mostly in the middle of the wall. I dug out the plaster where these had appeared and found in some cases an old rawl plug in the wall. I removed the plugs, pva'd the area, filled and skimmed this time with easi-fill, left to dry and sealed/ painted. Now 6 months later a few more have appeared some in different places and one in the original(where there are definitely no rawl plugs). I have also noticed the same flaking with a light brown staining coming up around where the edges of where the plug sockets are. After the sockets were chased out, I filled the edges flat with easi-fill and now this dark stain/flaking seems to be spreading from those too. The wall itself was an internal wall joining to next door. It was brick originally but was rendered with a solid type of cement render (but very hard to chip off) and none of the external walls have any problems (they were plaster-boarded with the foam-backed board for building regs). The rest of the project is at last finished, but I don't want to rent it out with these patches. I also don't really want to strip the whole wall back to brick and start again as obviously that means gutting the new kitchen. I thought first time maybe it was a reaction with some form of salt from the brickwork, but the truth is I don't really have a clue. Any ideas? All feedback, even if only on how to cover it permanently would be much appreciated.

 

[JohnD]

1) photographs please.

2)

the paint (which had been pva sealed)

Paint on PVA? Oh dear. Why did you do that?

3) How do you know there is no damp?

4) Some paragraphs will make it easier to read.

 

[SeaSpirit]

Please find photo's attached - I haven't included the random circles, because they are faint on a picture and so difficult to make out (but obvious when you look with human eyes). I have included where it has happened near the plug sockets. The effect is the same though - paint that almost 'fizzes' and flakes off (I haven't touched it - it just falls off naturally), in some cases changing to a brownish colour, but mostly just reacting with something forming a roundish shape and flaking off. I just suddenly find a pile of paint dust sitting on the top of the tiles (which I haven't grouted yet in case there was a problem).

When I say paint on pva, I mean I sealed the plaster skim coat with a watered-down pva, prior to painting, which I thought was the correct procedure to 'seal' the fresh plaster.

I assume it is not damp because - a) the marks are mostly in the middle of the wall, b) the wall adjoins to next doors' kitchen which doesn't have damp C) none of the outside facing walls have any damp, d) Most of the patches I dug out and patched have not come back (though others have emerged) and e) The worst areas on this occasion are around the plug sockets. I may of course be incorrect as I'm not an expert, but that is my reasoning.

Please take a look and let me know what you think, many thanks

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• SeaSpirit
• 3 Jul 2013
• 1

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• SeaSpirit
• 3 Jul 2013
• 1

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• SeaSpirit
• 3 Jul 2013
• 1

 

[Alastairreid]

Condensation!

The exact same as i get in my porch in winter

I keep meaning to install a couple of vents.

 

[JohnD]

When I say paint on pva, I mean I sealed the plaster skim coat with a watered-down pva, prior to painting, which I thought was the correct procedure to 'seal' the fresh plaster.

no, pva is water soluble, and it prevents the paint from soaking into the wall and adhering to it.

emulsion is liable to bubble and come away when it is lying on glue.

if there is any damp the glue will soften and the paint will become loose.

The correct procdure is to prime the wall with mists coats of emulsion thinned with water, which soaks into bare plaster and enables subsequent coats to adhere.

there are still a few plasterers who recommend putting glue onto plaster, but most of them have been killed by angry decorators.

 

[Alastairreid]

there are still a few plasterers who recommend putting glue onto plaster, but most of them have been killed by angry decorators.