Redecorating wall that has peeling emulsion on slightly damp grey plaster


A bedroom I want to redecorate is in an extension which was built about 20 years ago. I started stripping the old wallpaper off and underneath, I find that the previous owner plastered the walls with grey plaster and then painted emulsion directly onto the plaster. Unfortunately one of the walls is very slightly damp, i.e., the grey plaster looks noticeably darker in the slightly damp areas than the really dry areas. And in the slightly damp areas, the emulsion is blistering (perhaps due to me pulling the old wallpaper off) and in those places, the emulsion is fairly easy to peel off.
What would be the best way to approach redecorating this room? Should I attempt to get all of the old emulsion off? I hope I can avoid that extremely arduous chore.
Could I just peel the loosest of the emulsion off, and then paint the slightly damp areas with damp block, and then repaint the whole room in emulsion?
I'd prefer to end up with painted walls rather than papered walls.
I recall a similar situation in my previous house, and a builder commented that "they used the wrong plaster" (i.e., it was absorbing moisture more than if they'd used the correct plaster). I think I painted the walls with damp block and then top-coated with emulsion, and the result was surprisingly satisfactory. I didn't get any blistering or mildew appearing even ten years later when I sold the house. So perhaps I should use the same approach in this house. I'd appreciate your comments.
It's is verry difficult to determine the cause of the dampness. It could be penetrating damp, althought the walls do have cavities. I don't want to go to any great lengths to find the cause; I'd rather just paint over it and seal it in!
Al
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AL_n wrote:

Is it your house or someone else's?
If it's yours, you are better finding the cause, rather than just sticking an elastoplast over it and hoping for the best. As you've already pointed out, it's got a cavity, and as it's only 20 years old, I'm presuming an intact plastic DPC, which doesn't leave many possibilities for what's causing the damp.
My guess (without seeing it obviously) is a leaking gutter and/or downpipe on the outside - whatever is causing this damp is outside, so get your jacket on and go and have a look, report back when you find out.
A small dehumidifier will dry it out in a few days once the cause has been rectified and then you can decorate it however you like.
I can't understand why people look for the 'easy fix' in situations like this, I remember years ago being called out to re-plaster someone's wall at the side of the back door.
It had been re-plastered half a dozen times in the past, and also had tinfoil glued on it, painted with bitumen and all manner of damp-stopping chemicals applied to it, and in all that time, the owner had never thought to fix the leaking pipe outside - he must have spent almost a grand over the years patching this bit of wall up and watching it bubble and flake off, when all it took was for me to drill one hole and insert 1 screw and he never had damp again.
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Phil L
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...Thanks for the reply. I own the house. It is true that the guttering is missing *near* the damp rea, but actually the dampest part of the wall is on the gable end which doesn't (and never did) have guttering.
The dampness could also be caused by a window that has a lot of condensation dripping off the pane and onto the sill, probably because I'm heating the house with the gas cooker downstairs, to save money (as money is *extremely* tight indeed at present).
The dampness really is only slight. One can only just sense it by touching the wall, so It's not a really major worry. In fact, it alread seems to have almost dried out where I have peeled the emulsion away yesterday.
Relacing the window and fixing the guttering are on the agenda for the Spring, along with dozens of other major repair jobs. I bought the house 9 months ago and it needs a lot of work.
Al
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On 04/01/11 23:56, AL_n wrote:

aha , lots of condensation from a gas cooker, which will condense on the coldest areas, so a bit of insulation on the wall would warm it and the condensation would happen elsewhere...
i know people sho used to heat their caravans with gas, then had to leave the windows oven cos of all the condensation.
get a woodburner? that will warm and ventilate.
I'm just heating one room with electricity.
[g]
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2 typos corrected.. On 08/01/11 23:30, george [dicegeorge] wrote:

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Just leave it exposed fora bit and the damp should dry off. Damp block would stop that, not really whats wanted.
You're left with an uneven surface. You could paint it, but it wont look good, better to put lining paper up first. You do need to remove anything loose, sorry.
NT
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Thanks, NT.
I wondered about the "seal it in, or not" issue. I wonder if there is some kind of porous emulsion, that lets moisture pass through and evaporate..
I rmember years ago, finding some "breathable" (supposedly, at least) paint for painting wood. The advertising stated that the paint would allow moisture from the substrate to evaporate out, but rain would not penetrate (a bit like "Goretex" fabric, in that respect).
Al
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Use of the term breathable on paints by manufacturers is close to meaningless. The question is how breathable. Simple lime paints are very breathable, emulsion less so, oil based paints much less so.
Lime paints also have a slight filing effect, and would thus reduce the amount of unevenness if you chose not to paper line or skim. Much better to line it though.
NT
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I wondered about lining. That would nicely cover up all signs that some of the emulsion had been peeld away.
On top of the lining paper, what would you suggest? Lime-based paint? Or matt emulsion? I'm concerned about the substrate becoming damp so that the lining paper ceases to remain stuck down well.
Or maybe I should line with a pourous, but finished wallpaper, so that no painting is necessary....
Thanks,
Al
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Both would work. By now I've forgotten what the construction type was. If its a pre-dpc non-cavity wall, lime is a lot more porous than emulsion, aiding evaporation, but you need to dilute it thin and use a few coats to get a good finish to rival modern paints.
http://wiki.diyfaq.org.uk/index.php?title=Limewash
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