Paint bubbling on ceiling

Dvnfermling

My son has been painting his ceiling with crown emulsion and the original paint looks like it is bubbling under the new coat. We think this is the first time the ceiling has been repainted since first build. I have googled this problem online and a solution appears to be giving it a coat of pva first.
My question is would the screwfix no nonsense product do this job and if so should it be diluted first ie 1.1 mix with water.
https://www.screwfix.com/p/no-nonsense-pva-5ltr/57248?tc=XB3&ds_kid=92700058024393114&ds_rl=1249407&ds_rl=1241687&ds_rl=1245250&ds_rl=1245250&gclid=Cj0KCQjw0K-HBhDDARIsAFJ6UGgmO980JHf_O8YE48yimX8HA6kDY5cIfnXt29KLv7XA4f-2eFUoBzUaAlQuEALw_wcB&gclsrc=aw.ds#BVQAWidgetID

Grenage

No PVA on any surface you plan to paint; it's the worst thing you could do.

Sand the affected areas and repaint; bubbling is usually down to dirty/oily surfaces or trapped moisture.

NSG666

If it's happening as he applies it I recently watched some youtube videos by a user Painting & Decorating (could have been called something like 'overcoming problems with emulsion'). In it they basically say to go as quick as you can with the first coat and don't go back over the same area.

Painting and Decorating - YouTube

Jeepers_Creepers

As said above - if the water in the new coat is softening and lifting the layer underneath, then apply that first coat sparingly and quickly - don't keep rollering over it.

NO to PVA! If you think what you have now is bad, wait until you try and emulsion over PVA - a rough sticky mess...

I have used stabilising solution before on troublesome surfaces - Everbuild 406 is cheap and effective. Roll on a coat - it's watery stuff - but check it too doesn't lift the paint before it dries. If you get that on successfully, you should be fine.

Dvnfermling

Thank you all for the replies, I'm so glad now I asked the question before going to buy this tomorrow. The ceilings are in a bedroom and living room so not dirty or oily as may be expected in a kitchen. But the issue is probably with the repeated rollering over the same spot.
I will clean off the bubbled parts and apply filler and then smooth off before sparingly painting it until we get an even finish.

dcfc67

If you are going back to show bare plaster then don't apply filler on the bare plaster. use a thinned down (20% water) coat of matt emulsion which will absorb into the plaster and provide a sound surface to fill any imperfections.

I find one time to be a great filler as its minimal filling and virtually dust free

Jeepers_Creepers

If it's not a typically troublesome room, Dvn..., like a bathroom or kitchen (ie steamy, greasy), then it's likely that the original paint just wasn't applied properly - eg slightly thinned so's it soaks in to the plaster - called a 'mist' coat. Or the plaster wasn't cleaned up or perhaps keyed before painting - eg it was too dusty or 'polished' to allow the paint to soak in.

Anyhoo, give it a light sanding - 120 to 180 grit - just to get rid of the wee bubbles, and then try (say on a 2m2 test area) a fresh coat applied fairly briskly and without too much over-rollering. See if that dries ok.

If it still reacts/bubbles, then lightly sand again(!) to remove bubbles when dry, and try rolling on a coat of 406 (again, try a test area first). Let it fully dry. If it looks ok, then chances are it'll be fine to take paint from now on.

The good news is that, being the only coat applied, the 'problem' paint on there will be thin, so once the bubbles are sanded down - should be peasy - it's unlikely that the revealed paint layer 'steps' will be all that obvious, and fresh paint will likely cover it without it needing filler. (Using filler for such jobs is a 'mare - try and avoid...)

Any chance of a photo to show the issue, and size of bubbles?

Dvnfermling

Any chance of a photo to show the issue, and size of bubbles?

I'll be heading back to his house tomorrow to help paint his fence and will have a look at the ceiling to see if the bubbling is still there.
Thanks again for advice.