Plaster peeling off.. ?!

This topic was probably mentioned in the past but I would appreciate some advice please.

Our bathroom had 2 layers of tiles bottom to top everywhere for probably last 50 years (ex-council house built in '54). I ripped it off, called a plasterer, he did the plaster & skim it. I waited for it to dry out. I painted with mist coat first. When I finished painting I noticed a slight air bubble in one spot so I took an old putty knife and it went off like a cheese. I called the plaster guy back. He ended up re-doing most of one wall but I was of opinion that everything needs to be ripped out and re-done. He disagreed so I respected it as he's the pro doing for $$. Again I waited 3 days for wall to dry, & painted. Then I noticed *other* wall had the same problem... it's coming off way to easily. See pictures below. And the plaster on wall that he's re-done recently is also coming loose..WTF !!

Why is this happening?? Has the plaster dried to quickly? Terrible job by plaster guy? Walls "cursed" ??

BTW it's rather dry underneath the plaster when I scrape it, most of it goes out like there's no tomorrow. The bathroom work is on hold, wife angry...

Thanks for your help.

More info: the walls are of bricks/concrete blocks with original render in places, where the bigger gaps were I filled in with easy plaster from Wickes (it holds very good). And the ceiling is plasterboard.

I'm not a plasterer, but that appears to be a very thin coat and the face of the original plaster has not been keyed, so the new will struggle to get a grip on the old face.

Harry Bloomfield said:

I'm not a plasterer, but that appears to be a very thin coat and the face of the original plaster has not been keyed, so the new will struggle to get a grip on the old face.

Click to expand...

Looks to be 2-3mm thick so no issues there. Not sure what you mean by plaster and skim, you plaster a wall or just skim it, did he pva the wall prior to skimming

He did plaster on more damaged walls, and skim other walls + skim plaster from prev day the next day if that makes sense.

He used PVA but:
1) first time plastering I noticed his PVA bottle looked very dirty and old. These things have best before date for a reason. He also complained the PVA doesn't dry quick enough (a bit impatient IMO).
2) second time when he came over to fix the peeling off on wall he then used my PVA that's brand new.

Both above cases gave same end-result: the plaster does not hold and can easily be removed. I can take a blunt putty knife and run along any given area and it just pop pop pop. There's only small sections where the plaster needs more work to be removed. The underlying surface (a easy plaster or original painted render) don't have much difference when it comes to adhesion for the plaster.

Sounds like a coating of Bluegrit or sand mixed with PVA prior to skimming would not have gone amiss especially if being applied to painted surfaces but the actual reason it didn't stick??