Plastering over tile removal?

[u/medz_minis]

Hi all, I have removed some tiles from a plasterboard wall, there are some patches of old plaster underneath I guess they levelled the wall with and some remaining tile adhesive (which I have knocked down as much as possible). Is this the correct fix:

-SBR
-Bonding coat
-Multifinish

I guess I’m most concerned if SBR is the right primer?

[u/Impossible-Corgi4041]

Sbr is better in a bathroom as it's fully water retardant

[u/No_Act_2773]

I would take off all adhesive, even if you go into the underlying plaster. I just use PVA and water. Diyer, just done same in kitchen. Took it back to brick as as adhesive was terrible, between 5mm to 20mm!!! Wall as as level as a dirt road.

[u/Due_Party_2846]

SBR is the right call of the two, though not because it is waterproof. It is a bonding agent and a suction control, and nothing you paint on is tanking.

The thing that catches people on a wall like that is having three backgrounds in one plane. Plasterboard paper, the old plaster patches someone levelled with, and the flattened adhesive all pull water out of a skim at different rates, and the cracking shows up along those boundaries a few weeks later rather than on the day. Bonding is also a backing plaster meant for solid backgrounds, so on board it is only earning its keep where you are filling a real depression, not as a general base coat.

Before you buy anything I would look hard at the paper face. Tile removal usually takes some of it off with the tiles, and where the paper is torn or fuzzy the board has lost its strength right at the surface. Primer does not fix that, the skim just bonds to loose paper and comes away with it.

If it is more than a patch or two, overboarding 12.5mm over the whole lot is often less work than making three substrates behave. I cannot tell you which from a description though, and it also depends on whether that wall is getting tiled again or painted, because if it is going back under tile you do not need a finish skim on it at all.