Why wont the paint stick to plaster????

ListysDad

To the OP.

As no one has explained what a 'mist coat' actually is and how it came about I will try.

Paint polymers are typically extremely long so consequently sit on top of a surface instead of penetrating - and creating a proper bond. What watering paint down (the mist coat) does is break down those polymers into much shorter lengths. They then have a much better chance of penetrating the surface and giving the subsequent normal coats something to grab hold of.

If the plasterer has left a surface to be painted highly polished to give a better impression of their abilities, you'll need to run some glass paper over it before the mist coat. The reason for this is that a highly polished surface is much more compacted so by sanding it you are opening it up and it's then much more able to receive the modified polymers

If you can be bothered, as previously mentioned, it's better to build up layers to give better and better adhesion. This paint will then last longer in a damp environment like a bathroom but is not really necessary in normal areas.

nickj_2

if you rub the surface where the plaster has come off this will tell you where the problem lies , if it is powdery then the walls should have been pva'd before plaster applied ,it may be the plaster that is powdery or it could be distemper paint which was used before modern emulsions , this should be tottaly removed before plastering . if it is not powdery try putting a drop of emulsion on the bits where the plaster has come away , it may be that the paste was not removed from the wall before being plastered , if paste is still there it will be reactivated by the emulsion and you may see it buuble up a bit ,
what ever the cause , it is not your painters fault , the problem lies on the old wall surface and the new plaster

Lucy_DIY

Thanks chiefgoobster.

The whole lot of plaster is coming away, and revealing the bare wall beneath, which isn't bare brick but a starchy papery surface (which scratches away and probably should have been removed before plastering).

No moisture has got into the wall. The Dulux paint suggests leaving 6 hours to dry between coats, and I think more likely my decorator left 3 hours.

Because it's the plaster falling away and not the paint it makes me think the plasterer is at fault. But maybe I'm wrong.

keystone

I agree with Nickj. I would definitely say that the spread is at fault here.

Cheers

nickj_2

Lucy_DIY wrote: »

Thanks chiefgoobster.

The whole lot of plaster is coming away, and revealing the bare wall beneath, which isn't bare brick but a starchy papery surface (which scratches away and probably should have been removed before plastering).

No moisture has got into the wall. The Dulux paint suggests leaving 6 hours to dry between coats, and I think more likely my decorator left 3 hours.

Because it's the plaster falling away and not the paint it makes me think the plasterer is at fault. But maybe I'm wrong.

is the starchy paper wallpaper? if so this should defiinately be removed
the only paper (ish ) surface that can be plastered is plasterboard

i think what has happened is that the moisture from the plaster has loosened the paper and made it unstable , then if your painter has used a roller then the suction from the roller sleeve would just pull away any unstable plaster .
i cant actually believe a decent plasterer would plaster over paper

keystone

nickj wrote: »

i cant actually believe a decent plasterer would plaster over paper

Neither can I but I looked at a potential job today for a DIYer in trouble on my way home where thats exactly whats happened. Skimmed over woodchip. Don't think a proper spread did it though - its a pigs breakfast.

Cheers

ListysDad

We find that all the time when doing bathrooms. Most of the time tho it's the tight fisted who cannot be bothered to take the paper off and are about to sell leaving the poor sod moving in to pick up the pieces and make good...

chiefgoobster

ListysDad wrote: »

We find that all the time when doing bathrooms. Most of the time tho it's the tight fisted who cannot be bothered to take the paper off and are about to sell leaving the poor sod moving in to pick up the pieces and make good...

exactly !
why don't people do a job properly in the first place ? Do it once so that you (especially the Tradesman) doesn't have to return to the job.

chiefgoobster

LucyDIY

I think in the end it's the plasterers fault. Sorry but someone has got to take the blame.Maybe start again. I know it's aggro but the end result will be worth it. Leave each paint coat for as long as you really can , overnight if poss.

Rome wasn't built in a day.