Paint bubbling/blistering

badatDIY

Started painting a room with a white basecoat having prepped properly beforehand (sand and wash). Upon putting on the second coat in certain areas blisters stated forming (see images at bottom of post), some of these disappeared after a few hours but others still remain. Out of curiosity I popped one when wet and it would appear the original old coat of paint is lifting from the wall (the inside skin of the bubble is blue).

Two questions: 1) why is this happening? I originally thought too hot (room is very warm as south facing), but the fact the old paint is lifting suggests a very bad paint job by previous occupants? Unlikely to be moisture as no plumbing near there and it's not rained in weeks.

2) what do I do to fix it? Presumably I should scrape/sand any remaining bubbles, fill if necessary then perhaps prime? But which primer? I'm reluctant to use BIN because so expensive and smelly, but don't know whether peel stop, 123 or gardz is most appropriate. Also can I get away with spot priming or should I just suck it up and prime the whole wall?

https://ibb.co/tQcjtWj

https://ibb.co/kB1FV80 

Southend_2

I had this in my house. We thought it was due to old wallpaper paste in the walls. Painted over with PVA to seal it before repainting and all was OK.

FreeBear

Could be the new paint reacting with the old rather than poor adhesion - Short of stripping back to bare plaster, Zinsser 1-2-3 is going to be your best bet. Yes, it is a little expensive, but so is time and the effort to make good on the bad patches.

badatDIY

FreeBear said:

Could be the new paint reacting with the old rather than poor adhesion - Short of stripping back to bare plaster, Zinsser 1-2-3 is going to be your best bet. Yes, it is a little expensive, but so is time and the effort to make good on the bad patches.

Do I need to sand back to original paint then? Fairly simple to do where bubbles are, but if I prime whole wall sanding back will be a right pain in the !!!!!!

Simonon77

It could be a paint reaction. I have had this when using washable paints that seemed to react with something underneath, but only in certain areas 

badatDIY

Simonon77 said:

It could be a paint reaction. I have had this when using washable paints that seemed to react with something underneath, but only in certain areas 

Is there any chance it's a bad batch of the new paint? First coat of white went on fine, but then I had to buy and open a new pot because the old one ran out - it was only then this started happening (same brand and type - Dulux Matt ceilings and walls, which I've used as undercoat in other rooms just fine)

Mr.Generous

Almost nil chance its the new paint. Its either poor prep, a reaction to something on the wall or contamination if you painted from a kettle.

badatDIY

Mr.Generous said:

Almost nil chance its the new paint. Its either poor prep, a reaction to something on the wall or contamination if you painted from a kettle.

Gotta be a reaction then. So same question as above: I'll sand and fill where necessary already existing bubbles then use zinsser 123 on it, but is it worth doing the whole of every wall with primer and, if so, do I need to sand all the way back to the original paint before I started adding mine?

Mr.Generous

I've never encountered a problem bad enough to need all that, I'd just lightly sand the walls again then wash down with a very diluted sugar soap mix. The only time paint has lifted for me (many times because I'm impatient) is when applying a second coat too fast with a roller. Let the room dry completely before applying another coat - tempting though it may be to just start again as it looks dry and I have the roller right here still wet ....

plumb1_2

Are you painting over old silk Emulsion 

badatDIY

Mr.Generous said:

I've never encountered a problem bad enough to need all that, I'd just lightly sand the walls again then wash down with a very diluted sugar soap mix. The only time paint has lifted for me (many times because I'm impatient) is when applying a second coat too fast with a roller. Let the room dry completely before applying another coat - tempting though it may be to just start again as it looks dry and I have the roller right here still wet ....

Think I left it a good 12 hours last time, and in low humidity/high heat (hot weather, using dehumidifier to keep around 50%), but this time maybe I'll leave a whole 24 hours. Would you use primer? If so, which one?

plumb1_2 said:

Are you painting over old silk Emulsion 

Nope, over matt. The original paint job was very bad though, wall was covered in hairline surface level (i.e. just in the paint) cracks, so god knows what they painted onto or how! I assumed cleaning with sugar soap and sanding would be enough but clearly not