Truing up painted plaster

[Nigel Watts]

I have a plaster arch in a dividing wall on my second floor landing which looks wonky. The problem is less with the curved part than the verticals, which need to be trued up. The plaster all seems to be modern gypsum rather than lime and has been painted with several layers of modern emulsion paint (if it had been original I am sure the arch would have been done properly).

I am wondering how best to fix it. I think the easiest thing would be to fix a couple of battens, one on each side of the dividing wall, then plaster in between using the battens as guides for a straightedge to get it true. The question is how to get the new plaster to adhere to the old. I would rather not have to cut out all the existing plaster, but plastering on top of emulsion paint does not feel right to me.

 

[Feltwell]

If you're going to use Gypsum again Nigel - you may as well - then personally I'd score the existing surface in a criss-cross pattern to break the paint and give a key through to the underlying plaster, then PVA the whole surface before plastering. What thickness are you going to have to apply?

That or scrape the paint off, as it doesn't matter if you damage the underlying plaster. I'd still use PVA though, even if you do this.

 

[MdB]

If you're going to use Gypsum again Nigel - you may as well - then personally I'd score the existing surface in a criss-cross pattern to break the paint and give a key through to the underlying plaster, then PVA the whole surface before plastering. What thickness are you going to have to apply?

That or scrape the paint off, as it doesn't matter if you damage the underlying plaster. I'd still use PVA though, even if you do this.

I've done similar to a bathroom ceiling and that worked well.