Blistering paint mystery

[Michael Rosen]

I have a small patch of blistered paint from where the room was repainted last year. The previous paint ( which was on for about a decade was also blistered in exactly the same way. Can anyone guess what the issue may be and a remedy? This is an interior wall and the plaster is old. Behind the wall is a void which is under the main house floor.( This room is a side room which you have to step down into)

 

[Wayners]

Some kind of bridging behind that spot which is causing damp to blister under emulsion.
Probably lime plaster as old so don't coat with vinyl emulsion as will seal wall. I suspect that the emulsion is a vinyl?

 

[Michael Rosen]

Thank you. Yes it was a Dulux vinyl emulsion paint. What would be the best way to repair this?

 

[michealangelo]

If the painted area with the bubbled flaking etc patch is quite solid to the touch you could abrade it either with fine paper or use a light setting on a hand sander

I would then dust this off

Then I would apply alkali resisting primer as I think that looks like a typical paint on lime reaction

If this problem is small just cover the patch

If it seems to be a bit more widespread cover the whole wall

Alkali resisting primer can be bought from a decent decorators merchants

Dulux do one , Leyland do one , Zinsser Guardz is also used

It's very runny so apply carefully

Take note of drying time

Then once dry I would apply a slightly thinned coat of matt emulsion .......say a half pint glass of water to 2 and a half litres of matt emulsion.....not vinyl matt emulsion as stated above as it will peel off again .....

Once this had dried .....give it a day .....if the area needs filling do so with a general filler ......sand back

Then finish with the rest of your slightly thinned matt emulsion

 

[Michael Rosen]

That's very helpful. Thank you