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F Murtz

On 15/5/20 9:23 am, wrote:
On Thursday, 14 May 2020 14:33:14 UTC+1, Martin Brown wrote:
On 14/05/2020 14:12, R D S wrote:
On 14/05/2020 13:54, newshound wrote:

Old property? Potentially damp wall? Has the plaster been sprayed with
silicone? Does it have to look "good"? If not maybe undercoat with SBA??

It's an old property but was refurbed a few years ago, beyond that I
don't know. There's no damp.

Is the plaster actually plaster or an alkaline lime material. I have had
bother with that in places in my old Victorian building. But it was more
that the paint would cure OK at first and then gradually blister off.

pH test or litmus will show if the surface is strongly alkaline.

It doesn't have to look amazing but needs to not look a bag of..... but
i'm not spending 10 quid per litre on acrylic based paint!

I'll get as much off as I can scrape off and attack it with PVA* before
painting, or would lining paper be better?

* Suggested by a decorator in the family, but I thought that was a no-no?

and red cabbage juice can be used as a pH indicator.

For problem surfaces you can always paint a layer of oil based undercoat on first, solves most problems.

NT

Or try shelac alcohol base as a first coat then ucoat