Mist coat not adhering to new plaster

[NorthernTom]

I've had a bedroom plastered (ceiling and Walls). Finish didn't look great, but plasterer came back and said it should be fine when painted.

Done a mist coat on all of it today and there are patches everywhere that wouldn't really take the paint.

When I tried a second mist coat later it took whatever paint with it so abandoned that and found in places the paint just comes off in my hand.

I don't think it a case of it not drying out, but at a loss how to fix it/what the issue is.

Pictures below

 

[HERTS P&D]

What was the ratio of the paint-water?

Andy

 

[NorthernTom]

I did about 60/40, but where the patches are I can just scrape it off while other places it is fine.

One wall that was just skimmed is almost perfect, but there are a couple of very small patches that won't take any paint vs the mess in the pictures

 

[NorthernTom]

I only have one picture of pre painted room and it's a bit where the paint has mainly gone on okay - but how wondering if it hadn't dried out fully?

Looks bloody awful this morning. The very thin bit of paint on the patches no longer runs off, but won't take anymore paint

 

[opps]

I can't think of anything other than the plaster still being wet.

Other possible causes such as silicone contamination seem unlikely.

BTW, there is no need to water down the paint that much. The small print on the tin probably recommends something closer to 10%.

 

[ic1927]

Could be pva coming through the plaster or it's just been over trowelled making it glass like and impossible for the emulsion to bond. Try sanding it down and coating the bad areas with alkali resisting primer.

 

[opps]

Could be pva coming through the plaster or it's just been over trowelled making it glass like and impossible for the emulsion to bond. Try sanding it down and coating the bad areas with alkali resisting primer.

I did think about the possibility of over trowelling but it doesn't explain the tiny patches in image number 1.

 

[ic1927]

I did think about the possibility of over trowelling but it doesn't explain the tiny patches in image number 1.

Pva bleeding through is very likely here, either way, a sand down and some ARP will sort it out, done this countless times over the years for this kind of problem. Seen some painters use thinned oil uc but it's not as affective as the ARP, which is designed for problems with plaster.

 

[NorthernTom]

Cheers for the replies all. I've been scraping off some of the patches.

Couple of observations: in some places the plaster has tiny pinprick black dots on it. Fairly sure it isn't mold, but what could it be/does it indicate where a problem might lie?

Also - I discovered that where the paint appears to have gone on okay (not patchy) - it can be wiped off easily with a wet wipe. Im assuming this means the mist coat hasn't gone on properly - but is it not watered down enough/watered down too much/something else.

Thinking of getting a decorator in to sort now, but would like to understand the causes (how much is me/how much is the plasterer at fault).

 

[JohnD]

The black specs may be tiny flies that landed on the wet paint. Wiping with fine sandpaper will remove them, if so. More common if you've had the window open in warm weather, or in a kitchen, but the scent of alcohol or jam also attracts them.

 

[Dutchie007]

Pva bleeding through is very likely here, either way, a sand down and some ARP will sort it out, done this countless times over the years for this kind of problem. Seen some painters use thinned oil uc but it's not as affective as the ARP, which is designed for problems with plaster.

What is ARP? Do you mean would be need to sand the patches right back to the plaster or just sand the current paint over ?

 

[opps]

I suspect that @ic1927 is referring to alkali resistant primer.

Alkali Resisting Primer - Johnstone's Trade Paints

Johnstone's Trade Alkali Resisting Primer is a solvent-based primer and sealer for interior and exterior use on new or bare plaster, concrete, cement, render, or wood and metal surfaces.

www.johnstonestrade.com

I have only ever used it when customers have a light amount of salts being released to the surface.

If the plaster is still wet or damp, ARP will fail. The salts/moisture will often push the arp away from the surface.

I cannot comment on your case, given that you haven't told us anything. I might be prudent to create a new thread given that this one is 5 years old.