plaster: which one?

[Fred]

Hi,

I read here that out-of-date plaster was good for filling chases and B&Q were selling out-of-date BG Thistle universal one coat plaster so I bought that. It did the job but it seemed a bit grainy. Is that a sign that I didn't mix it well or is it a side effect of it being out of date, or is it just supposed to be like that (I was expecting plaster to have a smooth finish?).

The universal one coat goes on white. The British Gypsum site shows pictures of the bags but not the product on a wall.

I would like to try to plaster over a plasterboard. What plaster is best for that? When I have hired a plasterer they have always used a plaster that is almost brown when wet, that goes through various shades of pink as it dries. What would that one be?

TIA

[Tim Watts]

Fred wibbled on Monday 28 June 2010 09:40

"Finishing plaster" would be that one. No good for deep fills (it shrinks and cracks) - which is why they also do the one-coat.

do it in small bags, but seeing as the smaller bags actually cost more in absolute terms (more per bag not just more per kilo) than the 25kg bags on the same shelf, it's a bit pointless (unless you have to carry it home on the bus!).

[Andrew Gabriel]

I've never used one coat plaster, but I've seen same effect when someone else was using it. I suspect it's a compromise by virtue of being one coat.

I use out-of-date finish coat for this. Mix it up initially as a bonding coat (add a little PVA, or use out-of-date bonding coat if you have that too). Apply PVA to back and sides of chase, and fill with bonding coat to within a couple of mm of the surface. It will crack, but that doesn't matter. When that's almost set, mix up just finish coat to do the last 2mm and polish off.

Board finish or Multi finish plaster.

If the board is already decorated or sealed, you'll need to PVA it first so the plaster sticks. Search back in google for articles on how to plaster finish coat - there have been plenty of them.

[<me9]

Board finishing plaster. The colour depends on which factory(mine) it is from. Some is grey, others are pink/brown.

[John Rumm]

One coat is a compromise between a backing plaster and a top coat, neither as rough as one or as smooth as the other.

I tend to buy multifinish - it goes over backing plaster or plasterboard. Board finish may be slightly cheaper if just doing boards.

[js.b1]

Rather variable.

Fresh, particularly big bags, can be excellent. Old, damp weather & stored in damp outlet, particularly small bags, can be "like oatmeal & special k".

The larger bags, perhaps by virtue of their bulk or higher turnover, seem to survive poor storage better.

[Fred]

Thanks for everyone's replies. So board finish can only be used with new boards then? If I wanted to skim over some already plastered walls or boards would it not work as well? I was looking only to skim some new boards but thought I might have skimmed an already plastered wall if I didn't do too badly.

[John Rumm]

In which case multifinish would be a better bet...