Plastering preparation

[SemiDetatched]

I'm having to remove some large areas of old lime plaster from interior brick walls. I plan to put on a bonding coat and then a finishing coat. The brickwork is uneven and there's not enough clearance over the whole area to dot and dab even 9.5mm plasterboard. I need a little advice about preparation of the brickwork.

I'm going to remove all traces of the old lime plaster. Once that's done, should I then seal the wall with a PVA wash or will it be OK to plaster directly over the cleaned surface with bonding?

Secondly, can I/should I put the finishing coat on before the bonding is totally dried out (say a day or so) or does it need to be absolutely, totally dried out before the finish coat goes on?

Finally, I've blocked a doorway with a stud wall and plasterboard. Where the board meets the brickwork/bonding coat, should I be using something like scrim tape from the board to the bonding or is it OK just to skim over the join as is?

Many thanks,

Jim

 

[1john]

Pva will help control suction as the lime mortar will suck the hell out of the bonding, you can cover with finish plaster when it's firm enough or leave it to dry out and pva it then skim, the choice is yours.

Scrim will help around the door opening but unless the plasterboard overlaps the brickwork and has been stuck to it with board adhesive then a crack will always occur from the difference in expansion between the timber framework, the plasterboard and the brickwork. Two of three layer of scrim before the bonding coat and two or three after the bonding coat may add a bit of damage limitation.

 

[SemiDetatched]

Pva will help control suction as the lime mortar will suck the hell out of the bonding, you can cover with finish plaster when it's firm enough or leave it to dry out and pva it then skim, the choice is yours.

Scrim will help around the door opening but unless the plasterboard overlaps the brickwork and has been stuck to it with board adhesive then a crack will always occur from the difference in expansion between the timber framework, the plasterboard and the brickwork. Two of three layer of scrim before the bonding coat and two or three after the bonding coat may add a bit of damage limitation.

That's brilliant John, many thanks. There's no reason why I can't plasterboard over the old door, fixing to the frame with screws and onto the brickwork pb adhesive. I just don't think 9.5mm would go right over to the new door opening.