window board on top of plasterboard

[mk2phil]

When using plasterboard to level the window reveals before fitting a window board on top, do you need to seal the underneath of the plasterboard that will be facing the cavity?

I've read that you need to seal the bottom face of the windowboard if you were sticking it straight to the brickwork reveals, but if you're using the plasterboard method to level the reveals beforehand - after which you then gripfill the windowboard to the plasterboard - do you need to seal the plasterboard in the same way?

I'm just thinking that as plasterboard is porous surely you need to seal it?

If so, what would you use? On my windowboards I've used primer, undercoat and then a final coat of gloss, but with the plasterboard would you use PVA????

Please advise as I want to get it right.

Thanks in advance, Phil

 

[noseall]

you do not need to seal the plasterboard.