Paint bubbles and comes away when overpainting with new paint - any solutions?

Question

We've been in our newbuild (2017) a while and wanted to redecorate and change the colour in one of the rooms.

We cleaned the walls (drywall/plasterboard that still has the original builders' paint on it) down with sugarsoap etc, and let it dry and started painting using a normal water-based can of Dulux. The walls are dry, there's no damp and the RH is fine.

However when we started rolling into the existing paint, there were one or two places where the existing paint started to bubble and some even came away when I rolled over it using the roller (the photo is what happened).

I guess this is because the original paint that was put on there by the builders is either permeable or they didn't put down a layer of plasterboard sealant. At the moment, I am just spot filling these and overpainting, but I have several rooms to do and don't want to have to spot fill these as well.

Is there any way to seal the paint on the existing walls to stop it doing this, or do I have to completely strip all the existing paint off, and apply sealant, then repaint it again? Having to do that second option is pretty daunting especially as we have several rooms to do - and we also wanted to wall paper a part to, but are afraid that this will screw up as well.

Any recommendations on what I could use to fix this would be appreciated.

Answer 1

The most critical part of any paint job is the prep work. Usually, when you're repainting, it's reasonably obvious that the old paint is failing and you end up scraping and/or sanding the entire area, but in your case, it it isn't obvious, nor, for 4-year-old paint, should it be.

Any sealer you try to apply over the top will end up doing exactly what your paint is doing. Even if you spray it on, it's going to have a tight hold on a spot of paint that's going to come off the wall eventually anyway.

You could scrape all the walls, which would find any loose spots like this, but would take hours of work and you might not find anything that falls off.

I would suggest getting a sanding screen on a handle that will attach to your roller poles. This is the type of screen that the dry-wallers/plaster-boarders would use to sand smooth the joint compound when they're initially installing the plaster board. Use a fine grit of sand paper or sanding screen since your goal isn't really to remove the existing paint, but to break through, tear off, or otherwise identify these spots where the paint isn't well adhered in the first place. It won't hurt to give the whole wall a very light sanding - it will give the old paint a bit of "tooth" to help the new paint create a mechanical bond to it.

Once you've found one of these loose spots, you can scrape it until you've got all the loose paint removed then give it a light sanding to ensure that the edges to the new paint are smoothly feathered in (you don't want any sharp lines - they'll show through the new coat of paint). You'll want to thoroughly vacuum the walls, and maybe even wipe them down with damp cloths to ensure you've got all the dust off - any dust will be a prime spot for the new paint to start letting go. Prime these areas as appropriate (a small tin of primer should do for just the small areas) then apply your new finish coat(s) of paint as desired.

There is, of course, no guarantee that this will find all the loose spots and that you'll continue to peel up the original paint as the new stuff sticks to the loose old coat. In those cases, you're just going to have to go back to what you've been doing.