Flaking paint on plaster finish

Well, to start it off(there should be plenty of other advice) PVA under paint is one of the biggest no-no's there is.

You need a thinned emulsion undercoat/sealer on fresh plaster, and sometimes you may come across a quite polished part of plaster that doesn't take paint very well. really well thinned emulsion can be useful as a sealing coat here.


Mr. Handyandy - really

 

Problem's likely to be caused by an over-polished skim coat or no mist coat primer.

If the plasterer's worked away at the top skim of plaster until it's "as smooth as glass" then you'll have a similar problem trying to get paints to stick to it as if it really were glass...

I'm just repeating Handy really, but personally I'd sand down any affected areas with 240 grit sandpaper - it's fine enough that the emulsion will cover any sanding marks, but it'll also key the plaster surface and help the paint grip the surface.

Make sure you prime any sanded areas with a mist coat then 2 coats of emulsion and you should be okay.

Hope this helps

 

Philip,

I have sent two messages regarding your problem but neither have appeared. If this message reaches the board then I shall have another go.

 

Well, I tried again but it failed again. I'm obviously doing something wrong. Does the connection 'time out' if you take too long, do you know?

 

Your problem sounds like efflorescence, crystalline deposits which form on the surface of building materials such as bricks and plaster etc..

I would suggest that you scrape back the peeling and flaking areas to the bare plaster and dry brush away the salt deposits very thoroughly, also the same treatment to those deposits on top of the painted surface. Do NOT introduce moisture as this will risk further chemical activation. Now keep the walls under observation for one to two weeks. Should you see further salt deposits then brush them away dry. Keep doing this until you are fully satisfied that it is clear, be patient it may take a while. Coat the bare areas with a thin coat of flat oil paint or alklai resisting primer, lighly pigmented type. When fully dry continue with your wall paint. If it returns then post again.

Sounds like the original building materials may have been contaminated, perhaps the sand was loamy.

 

Thats for the advice Goodwill.

I was trying to think of that word, "efflorescence",
but it wouldn't come to mind, however thats
definatley the problem Ive got.

Efflorescence: literaly "Bursting out into flowers".

After cleaning it down and leaving it for a while to
see if anything comes back, and it doesn't, do I coat
it with normal gloss paint thinned down before
recoating with emulsion?.

Am I reading this right?

Not quite, do NOT apply any gloss paint. It is preferable not to apply any oil based coatings but it may prove helpful regarding your problem. Re-read my post above, I refer to FLAT OIL PAINT and ALKALI RESISTING PRIMER only.

In the first instance I would suggest that you proceed to remove the loose and broken paint back to a firm edge (in serious cases it may prove necessary to remove the paint from the whole of the affected areas). After brushing away the salt deposits you may wipe the bare plaster with a <u>hardly</u> dampened sponge to remove the residue (rinse and wring it often and thoroughly) but never wet these areas again, dry and thorough brushing only. Do the the same where the salts have permeated to the surface without breaking the paint film.

I will send you a further post next week.

 

Philip,

In your original post you said that you had "....tried all sorts from primers to PVA etc.". Exactly what have you applied, in what order, over bare plaster or over the existng emulsion paint or both? Regarding the PVA, was this a PVA emulsion paint or a PVA adhesive e.g., UniBond Super PVA Adhesive & Sealer?

 

Philip,

You cannot expect a coherent paint film if you lay one type of material on top of another like you have been doing. Keep on like that and you can expect additional problems to the efflorescence.

The effloresence, a test: Go to your local chemist and buy some strips of 'red' litmus paper. Strip back to the bare plaster one of the window reveals. Wet the wall thoroughly, wait a couple of minutes then lay the litmus paper on the wet surface. In the presence of alkali the red litmus paper wiil turn blue. Now using a good quality sponge and clean hot water wash this bare reveal very liberally and very thoroughly, three to four times, changing the water between each wash.

After a week has passed the plaster to the reveal should have dried out, now wet the suface liberally, wait a couple of minutes then lay another strip of red litmus paper on the surface and note the result.