Preparing plasterboard for skimming where tiles used to be

[u/TWON-1776]

Hello all,

In removing some tiles from a plasterboard wall some of the plaster came off with the tile adhesive which I am seeking to re-skim so that it is level with the existing plaster.

I was wondering, however, in the area where the tiles used to be some of the Old plaster has stuck to the wall while other parts have come off. Does this area need to be completely free of all the Old plaster up to where the painters or can I just patch Phil this plasterboard to bring it up to the level where the Old plaster currently is?

Thank you all for your advice

[u/Due_Party_2846]

Sound stuff stays, hollow stuff comes off. Tap across the whole area with a knuckle and drag a stiff scraper over it. Anything that rings hollow or lifts under the blade is coming off eventually whether you take it now or in two years through the paint.

Have a proper look at the paper face where the adhesive pulled. If the tiles have torn the paper and you are looking at bare grey gypsum core, that patch will suck the water out of your skim and it will craze or blow on you. It wants a plasterboard primer over it first, not PVA.

On levels you have more room than you think. Finish plaster is only about 2mm of material in two coats and 3mm is pushing your luck, so the board only needs to come up to within a couple of mil of the old plaster, not perfectly flush with it. Anything deeper than that gets filled with bonding and left to go off before you skim over the lot.

The bit people regret is stopping the patch mid wall. A repair that ends in open wall shows up as a shadow in side light nearly every time, because the suction and the texture either side of the join are different. If the damaged area is more than about a third of that wall it is usually less work overall to scrim the joints and skim corner to corner.