I have patched a gap in the ceiling plasterboard (where a room divider was removed) with plywood. This was used because the modern plasterboard (we call it Gib-board, but I didn't invent it) is thicker than the stuff they used 35 years ago for ceilings. I'm assuming that there is a way to prep the wood for plastering - what is it?
Hi Gib, Enjoying the World Cup? Or are you not into the Rugga? :) when you say the plasterboard is too thick are you referring to 9mm or 12mm board? because you get both here or is 9mm still to deep? If you're using ply how thick is that - 6mm? It depends how much space you have (thickness). You can heavily PVA the ply but it's still not great to skim over as it will flex more than the surrounding material and could crack at the seams. If really tight for space, remove the ply and pin building paper up there and cover it with EML mesh and then plaster over that... The building paper will stop the plaster from pushing through the mesh into the void.
HTH Deano.
It is a rather narrow strip of ply, 9 mm thick, about 12 cm wide, very securely screwed down onto a joist. Flexing is not an issue. I just want to know what to do to the ply to make the plaster stick. Primer?
The rugby is starting to get more interesting, Oz vs Ireland, SA vs Fiji, and Samoa vs Wales in the weekend.
A good 2 coats of PVA probably - 2nd one should be tacky, not dry when the skim goes on.
HTH
Tim
Thanks Tim. I've never used PVA - how long does it take to dry/become tacky?
Seems to be standard now when plastering anything that hasn't just gone on.
1st coat - diluted (1:3 or 1:4 IIRC). Let that dry (overnight). 2nd coat, 1:2 or thereabouts. If you put that on it will be ready to accept plaster in about 1/2 hour - 1 hour depending how hot/cold/damp the environment is.If it's too wet, the plaster slides off. If it's bone dry, you lose the benefit of having it. Tacky allows the plaster to get a bond to the substrate by slight intermixing of the bondary layer.
HTH
Tim
I've proved (to my own satisfaction at least :-) ) that pva tacky is no different to pva dry (or pva mixed with the plaster for that matter). Plaster initially slides off a sealed surface but, once suction takes over, it hangs on well and dries better than had it been only partially sealed.
When I wrote 'flex' I meant expand and contract at different rates to the surround. If the ply is 9mm why can't you just use 9mm plasterboard? if you have it already in and don't want to remove it then just go with the ply PVA'd. Just put it on with a little water in it, I sometimes dip the brush in neat water then neat PVA and let it mix that way. Wait until the PVA is almost dry (sticky to the touch) then plaster as normal. If it cracks at the edges in the future just fine surface fill and paint over... Scrim tape will help here as suggested in the thread elsewhere.
D.
Just to be sure - by 1:2 you do mean 1 part PVA to 2 parts water?
Yes - but it's not a precise art. Also, some bulk PVA is more diluted to start with (do not buy at B&Q).
The general idea is the first one is very watery to sink in and the second one should be a good deal thinner than pure PVA but no where near as watery as water, if that makes any sense -
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