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

 

[Michael Rosen]

Out of curiosity I already have a pot of BIN Aqua. Is this the same as Guards and could be used for this? Or should I use Guardz? Thanks

 

[Wayners]

Bin aqua will seal in stain but any damp behind will push it off with blisters and bubbles.
Might last a few weeks or months though.
That don't look like paint/filler failure.

Guess no harm in trying so carry on

 

[Michael Rosen]

Thanks. So I'll buy the Guards then as I just want to be sure it will work

 

[michealangelo]

Thanks. So I'll buy the Guards then as I just want to be sure it will work

 

[michealangelo]

I think to be safe I would use guardz first .....if there is a reaction between plaster primer and paint then the alkali resistant paint ...guardz ....should prevent the problem happening again

Putting the water based zinser plus on top of this alkali primer is OK and if you do I wouldn't worry about thinning out your emulsion as the zinser plus will act as a final primer .....if you didn't put the zinser plus on then go ahead and just very slightly thin your emulsion

I think warners is right and you are covering all options

 

[michealangelo]

Looking again it's definitely a lime reaction with the emulsion , it got that classic pattern

 

[Michael Rosen]

Thank you for your advice

 

[Michael Rosen]

So I stripped back the paint yesterday to apply a coat of Guards and this is what lies behind the blistered paint. There seems to be a darker spot within the plaster. Does this confirm the view above that this is a lime reaction with the emulsion in this particular patch?

 

[michealangelo]

So I stripped back the paint yesterday to apply a coat of Guards and this is what lies behind the blistered paint. There seems to be a darker spot within the plaster. Does this confirm the view above that this is a lime reaction with the emulsion in this particular patch?

Yes

Apply two coats of the alkali resisting primer

 

[Michael Rosen]

Thank you