Paint problems

[Britanicus]

I have patches of paint bubbling no matter what I've tried putting on it. It has zinnser damp block, and one coat satin but still bubbles. Any ideas??

 

[misterhelpful]

It looks to be a small patch of efflorescence which is usually caused by moisture drying out and pushing salts to the surface.
If there is any kind of moisture in the wall it must be allowed to dry out - damp seal won't stop a continuing moisture problem, so it has to be remedied first. Once done, you should dry scrape the area and sand back to a smooth surface. Don't add any form of moisture until you have applied a coat of alkali resisting primer and allowed it to dry thoroughly. Once this is dry, you can surface fill if necessary. Virtually every top name brand of paint will make such a primer, but it can be relatively expensive as it is usually in a 2.5L tin and you should only need a tiny amount, plus it is not a guaranteed cure for efflorescence (although it usually works) because salts can be a problem to cure.

EDIT:
If you or anyone else have any Zinsser Bullseye 1-2-3 Plus lying around, that also acts as an alkali resisting primer (but it must be the Plus version and not just the regular 1-2-3).