Plastering where tiles were

[reecec]

Hi

I have been finish plastering in a cupboard

One side of the wall was painted and the other had tiles.

When plastering over where the tiles had been the plaster instantly turns into a crumbly cement. When plastering where the paint has been the plaster went on fine. (I probably should have taken the paint off first but im just trying to get it to look ok its only a cupboard)

Is this to do with what has been used for the tiles as i did sand the wall down to remove the lumps where the tiles were.

Should I be adding a base coat plaster first. Or I will just plasterboard it first its only a small wall.

Any Suggestions,

Thanks

Reece

 

[Richard C]

Read through the archive posts & all will be revealed!

 

[reecec]

Anything to do with using PVA ??? to much suction

 

[Richard C]

Anything to do with using PVA ??? to much suction

Well done, you got it in one! Existing unpainted plaster will suck the water out of a new plaster skim coat almost instantly so you will never be able to get it on successfully without first priming the surface to reduce suction. Apply a couple of coats of 5:1 water/PVA first, letting each dry off & then apply a further coat of 3:1, let it go tacky & plaster away; but working time is limited!

The painted wall has less suction why is why it was more successful but you should still apply PVA before plastering. For sound matt emulsion, I apply one coat at 5:1, let it dry then 3:1 directly before plastering as above. If it’s Vinyl or oil based gloss paint, I scratch the surface with a stiff wire brush, or the corner of a scraper, apply a 3:1 PVA coat & leave to fully dry overnight; I then apply a further PVA coat before plastering.

IMO, plastering is one of the most difficult skills to learn so don’t expect too much but, as you say, it’s only a cupboard & that’s as good a place as any to start experimenting.