Painted over plastered walls which seemed dry but now have wet patches

Brigmeister30

Its been three weeks since we had our plastering done. We then began with a mist coat which went on fine and dried nicely then the next two coats and we ended up with some of the plaster peeling away. The plasterer has been to fix it but now we also have wet patches in the corners of the room from the paint. I feel like we have well and truly messed this up!! Any advice which will stop the plaster peeling away again once we attempt to repaint in a few weeks time! 

FreeBear

Plaster should never "peel away". Assuming it is a skim coat, what was on the wall originally ?

Brigmeister30

FreeBear said:

Plaster should never "peel away". Assuming it is a skim coat, what was on the wall originally ?

It was taken back to brick and fully replastered when it came off the plaster underneath was wet still but dry on the outside. Plasterer hinted that it hadnt bonded correctly but that also it could be our fault for not have the heating on all the time

grumbler

IMO, if a thick layer of plaster didn't stick to the wall, it was the plasterer's fault, not yours.

Jeepers_Creepers

This plasterer stripped off all the old plaster to expose the bare brick? Was all of that brick wall bone dry underneath?

He then applied a bonding coat and the finishing skim layer over that? That was 3 weeks ago, and the skim coat had dried out fully, going pale pink?

When you say the 'plaster is peeling away', which layers of the above are you referring to? And when you say 'peeling' rather than, say, flaking or lifting, are you saying that this layer is flexible like a soft sheet? How thick is it?

Brigmeister30

Jeepers_Creepers said:

This plasterer stripped off all the old plaster to expose the bare brick? Was all of that brick wall bone dry underneath?

He then applied a bonding coat and the finishing skim layer over that? That was 3 weeks ago, and the skim coat had dried out fully, going pale pink?

When you say the 'plaster is peeling away', which layers of the above are you referring to? And when you say 'peeling' rather than, say, flaking or lifting, are you saying that this layer is flexible like a soft sheet? How thick is it?

it was taken back to brick and the wall was dry there was then some kind of boards put on as you can tell i am no expert!  It was unibonded and pva’d? Then plastered. It came off with the roller the whole plaster in one area and was damp underneath the plaster but completely dry on the outside

FreeBear

Sounds like a dot'n'dab application of plasterboard to the bare brick and then skimmed over the top. One does not slap PVA (or Unibond) on fresh plasterboard.

Putting PVA on a questionable surface helps to stabilise it if it is friable and also limits the suction (i.e. how quickly the wall sucks moisture out of the plaster). Letting the PVA dry gives you a reasonably waterproof coating that fresh plaster will have difficulty sticking to. Skimming should be done whilst the PVA is still tacky.

Brigmeister30

FreeBear said:

Sounds like a dot'n'dab application of plasterboard to the bare brick and then skimmed over the top. One does not slap PVA (or Unibond) on fresh plasterboard.

Putting PVA on a questionable surface helps to stabilise it if it is friable and also limits the suction (i.e. how quickly the wall sucks moisture out of the plaster). Letting the PVA dry gives you a reasonably waterproof coating that fresh plaster will have difficulty sticking to. Skimming should be done whilst the PVA is still tacky.

Thanks any advice on what to do in my situation?

FreeBear

Brigmeister30 said: Thanks any advice on what to do in my situation?

Cross your fingers and hope that the plasterer has done a "proper job" this time.

If the plaster flakes off again, he will need to use something like FeBond Blue Grit after roughing up the surface to give a decent key. But be rest assured, not having the heating on is not the cause of the problem - A slower drying time reduces the chances of the plaster cracking as long as you don't let it get too cold (anything under 5°C is a problem).

Brigmeister30

FreeBear said:

Brigmeister30 said: Thanks any advice on what to do in my situation?

Cross your fingers and hope that the plasterer has done a "proper job" this time.

If the plaster flakes off again, he will need to use something like FeBond Blue Grit after roughing up the surface to give a decent key. But be rest assured, not having the heating on is not the cause of the problem - A slower drying time reduces the chances of the plaster cracking as long as you don't let it get too cold (anything under 5°C is a problem).

Thank you so much for the advice! You read so many things and people say having too much heating on can lead to cracking of plaster which is why it confused me when the plasterer tried to insinuate it was our fault! 

Jeepers_Creepers

Brigmeister30 said:

it was taken back to brick and the wall was dry there was then some kind of boards put on as you can tell i am no expert!  It was unibonded and pva’d? Then plastered. It came off with the roller the whole plaster in one area and was damp underneath the plaster but completely dry on the outside

As FB says, that sounds like D&D - plasterboard sheets stuck to the wall using drywall adhesive 'Dot and Dabbed'. That's fine - it's a quick way of achieving a good surface ready for skimming.

A bit concerned by the 'unibonded and PVAd' bit, tho'. (Unibond is a 'make', and includes PVA in its range). The attached plasterboards sheets do not - absolutely not - require PVAing or anything else prior to being skimmed - it is already the perfect surface for skimming. PVA is only used for 'problem' surfaces - dusty, flaky, variant.

So, if he did use PVA, the question is 'why'? I can't think of any 'valid' reason, but wonder if he thought this would speed up the whole process? Eg, when you apply these dabs of drywall adhesive (a powder mixed up with water for use), the multiple points where they make contact with the plasterboard will likely be damp for a few days or more - plasterboard is porous. Did they think they'd be evening-out the surface by coating it with PVA first? If so, that's a poor call, I think. The PVA would simply slow down the dab drying process, and just not dry where it's in contact with dampish surfaces; it would remain 'active' - ie not 'set' -  where there is damp still coming through the boards from these 'dabs'. It wouldn't be a surprise, then, that on multiple spots on these boards, the skim simply did not adhere as it was applied to wet PVA.

It's hard to know what went on for sure, but if they really did PVA the boards, they need a good slap.

I'd certainly say that their reasoning doesn't hold water. Plaster skim sets chemically, and not by drying out. Even if it's still looking dark pink and clearly damp after a couple of days, it is still fully adhered to the surface below. Applying paint to this should not lift it or cause it to peel; the worst that'll happen is that the paint itself won't stick, and the paint peels off - leaving the plaster still on the wall. That fact that it's the plaster skim wot's come away suggests a strange process was followed, and the skim never adhered properly to the boards.

Anyhoo, as long as they fixed it, that's fine - but I can only conclude it's their issue, and not anything you've done. As for the remaining damp patches, leave these alone until they fully dry out before applying a second coat.