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Bubbling Supermatt on new plaster


 
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iceburging

from United Kingdom

Joined: 20 Apr 2012
Posts: 3
Location: Oxford,
United Kingdom

PostPosted: Fri Apr 20, 2012 7:03 pm Reply with quote

Hi all,

I have recently had aground floor room plastered and I am having trouble painting it (would you believe!).

To start at the beginning the wall in question is an old rubble filled rough stone wall. We hacked all the plaster off and have had it re-plastered. As far as I know the plasters first stabilised the wall with PVA then they applied a 3:1 washed sand cement mix with water-proofer and followed up with two coats of plaster and a skim coat to finish.

Now the nature of the wall is such that the depth of material could be approaching 6" in fact I'd say the total depth of material could be anything between 1" and 6" depending upon the profile of the wall.

Having read up on how to treat fresh plaster we first left the walls to dry out for 8 weeks. I also realise that with this depth of material it could take months if not years for the walls to dry properly so we decided to hold off with the fancy coloured paint and just go with a few coats of white Dulux Supermatt.

I have applied and initial coat of Supermatt diluted to 1:3 water to paint with a roller and this seemed to take to some areas better than others. I waited a day for this to dry and then set about the next coat this time diluted to 1:5 water to paint. This time I noticed small areas of the base coat lifting off as I ran the roller over the surface. Upon closer inspection I could see small regions < 1cm2 where the paint was bubbling. These then lifted off when I ran the roller back and forth over them.

Now the paint has dried most of the bubbles are no longer visible although some have cracked and started to peel. I have however noticed that there are small areas on the wall where the back of my finger nail will cause the paint to simply peel off the wall in these small areas of paint seem to be particularly soft whereas in others it seems perfectly hard!

Does anyone have any suggestions as to what may be going wrong and how to go about fixing it?
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joe-90

from United Kingdom

Joined: 28 Oct 2005
Posts: 29255
Location: United Kingdom
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PostPosted: Fri Apr 20, 2012 7:08 pm Reply with quote

Well it sounds to me like you did everything right. My guess is that the plasterer wasn't too hot and he's used too much PVA which had contaminated the plaster skim.
If I'm right then you'll nee oil undercoat to stabilise it.

Have a listen to what the others say first though as I can only guess from here.
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iceburging

from United Kingdom

Joined: 20 Apr 2012
Posts: 3
Location: Oxford,
United Kingdom

PostPosted: Fri Apr 20, 2012 7:20 pm Reply with quote

Thanks Joe.

Guess it could be contamination but the PVA application is under a good inch of material minimum and the skim was put on 5 days after the PVA was applied.
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joe-90

from United Kingdom

Joined: 28 Oct 2005
Posts: 29255
Location: United Kingdom
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PostPosted: Fri Apr 20, 2012 7:25 pm Reply with quote

You use PVA to control the suction when skimming - it's not the old stuff I'm talking about. Was the wall pale pink when painted? When you say it didn't take - did you mean it seemed a bit waterproof?
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iceburging

from United Kingdom

Joined: 20 Apr 2012
Posts: 3
Location: Oxford,
United Kingdom

PostPosted: Fri Apr 20, 2012 10:15 pm Reply with quote

Ah right. OK. Yeah the wall was pale pink. Not entirely uniform though there was the odd slightly darker swirl which seemed to match the patterns they made on the base coats (presumably to provide a key). Also yes you are spot on the bits that didn't take did seem a bit waterproof. I thought perhaps they had been over polished but you think this could be PVA contamination instead?
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joe-90

from United Kingdom

Joined: 28 Oct 2005
Posts: 29255
Location: United Kingdom
Thanked: 855 times

PostPosted: Sat Apr 21, 2012 10:09 am Reply with quote

Sounds like it to me. Oil undercoat is the best way if that's the case.
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