Stainblock showing through after painting over with emulsion

9 Oct 2010
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United Kingdom
Any suggestions please? I'm painting newly plastered walls I put stainblock on what I thought might be damp patches coming through. I then painted the walls with two coats of watered down emulsion. The stainblock was still showing through. I then painted on a coat of dulux matt emulsion. The stainblock is still showing through and seems to be stopping the paint soaking in. Would I be better using vinyl matt or vinyl silk instead of matt emulsion to get a better purchase and stop the stain block showing through?
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Were the walls bright pink or still damp?
The walls were pink - plastered 6 or 7 weeks ago. But there were a few dark stains which I thought might be damp coming through from the old plaster
Which stain block did you use?

Regardless, stain block is not designed to cover damp. It is supposed to prevent the water in the emulsion from reactivating old satins from previous damp. Unlike the following

If the wall is still drying then it might be ok in a couple of weeks. That said you could just use oil based undercoat or shellac based paint such as zinsser BIN which will be touch dry in minutes.

The stain block prevents water passing through so the emulsion will not soak in, rather it will sit on the surface (not an problem)- if your emulsion is the DIY dulux (ie doesn't say trade on the tin) then you might just need another coat or two on the problem areas

Btw Vinyl matt and matt emulsion are the same thing.

Both will allow any residual moisture to evaporate where as vinyl silk would trap it.
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Good advice from both Joe and opps here, one point though were the walls subject to damp before they were re-plastered.


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