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Undercoating and painting over unsightly damp stains


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I need to ask about covering previous damp patches with paint. We have a couple of patches that were once prone to condensation and where new plaster is not drying properly in our new kitchen – they are not wet, just more unsightly due to condensation point. I need to point out that the unsightly patches seem to be not a result from lots of penetrating damp.


I have read about Polycell damp sealer paint and it seems that this can be applied to dampish areas before applying an emulsion layer – any other suggestions will be greatly appreciated. Then I have read stories that some emulsion paints can show up the stained areas quite badly but others don't and it seems it comes down to the type of paint (silk, matt), whether it is water-based or oil-based and the manufacturer (we will go for quality, not cheap). it is also for use in the kitchen so obviously there will be steam and moisture in the air.


Can anyone advise on what sort of pain and/or undercoat we will need. one further minor problem is that my wife is quite particular about the colour of the finished walls but I guess we could get colours mixed anyway.


I have just noticed some fine white mould on the exterior wall in the alleyway and now wondering if this has anything to do with the unsightly areas inside – they do seem to mostly be in the same place yet others have no sign inside.

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Thanks guys,

There is a small damp patch in the corner of the kitchen by the door – no problem with guttering or door seals but is about 25cm high by about 20cm wide. It is not damp any more but used to be a site of condensation. Immediately outside this area in the alleyway, there are a few bricks with white mould on them. Another small patch is about 1 metre from the ground and is two circles of about 5cm diameter. Again, not actually wet to the touch but there are bricks immediately behind in the alleyway that have white mould.

i will try thr spary-on damp proof stuff and an oil based paint as an undercoat. I was just worried that any water-based emulsion over the top of the undercoat would bring through the damp patch.

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  • 3 years later...



I have the same problem around staircase on the internal part of an external wall. The dampness was fixed, new rendering on inside wall but after decorating just 1% of area gets stains back not wet though. I have used damp seal as undercoat several times and then water based paint but didn't help.


I will appreciate if you provide the solution worked for you in the end?


Many thanks

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This sounds like penetrating damp, not condensation. The white mould you describe on the bricks outside is more likely to be the salts coming out of the bricks as they dry out in the summer weather. You need an experienced builder not paint.

I am guessing that both your houses are of the older type and they have what is known as a solid wall not actually solid but with a very small gap in the middle of the double wall construction and a brick laid across the two walls to tie them in (together) at intervals. Sometimes some of the bricks become porous and sometimes the pointing(which is the cement between the bricks)allows water in. This shows as damp patches. You may also have a problem with rising damp.

Do not despair these problems are all curable but they are more expensive to fix than buying a tin or two of paint. Better to get it attended to as soon as you can. You may need to talk to the bank, after you have spoken to at least three builders, best to get some recommendations rather than look in the telephone directory.

Edited by Margarita Ma
Added info.
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