Plaster mix for wall?

[AndyDavis]

I've taken all the old plaster off the bedroom walls, down to the brickwork, and want to plaster the whole lot. Is it better to do a multi-coat plaster (how thick each coat?) rather than a single coat with bonding plaster and PVA? I've heard using PVA can result in condensation problems because the walls can't breathe.

 

[TexMex]

If you're back to bare brickwork, you could, technically, use the one coat stuff. If you do you'll probably regret it. This stuff is particularly unforgiving of poor technique.

Bonding is the right stuff for the job. rake out the joints a bit before you apply it, to give it a key. As long as you make sure you have removed all the loose stuff from the wall first, you shouldn't need the PVA. It's worth washing it down, thouroughly with water, to remove all traces of dust, then apply the Bonding about 10mm thick.

Bonding, is not intended to give a finish though. You'll still have to go over it again with finish (at about 2-3mm thick). Although this means that you are going over the whole job twice, it's still easier than using the one coat stuff.

 

[murraysnudge]

That's interesting you say that Tex because I think the opposite. I've used one coat stuff but apart from being expensive I find it takes too long before you can float it. this would be a good point for the beginner to plastering surely? I personally like to cement render with a skim coat. The skim coat requires a bit of experience and if you've got a big wall and doing your own labouring it does get a bit busy.
Each to his own perhaps? Agree pva not required though.

 

[TexMex]

used one coat stuff but apart from being expensive I find it takes too long before you can float it

You've hit the nail on the head. You probably have the experience to know when you can float it, and when you can't. Trouble is, some newbe puts it on the wall, gets it nice and flat, tries to float it, tries to float it, tries to float it, finally two hours later, get's in a panic because they've got little mounds, all over the place, and now it's going off

 

[murraysnudge]

Nice one Tex ; you're probably right.

 

[legs-akimbo]

If you are back to bare brick then I would reccomend a couple of coats of 3:1 p.v.a. not for bonding purposes but simply to reduce the fierce suction you will have on exposed brick. One coat is useless... bonding is a sticky messy pain in the arse and if left more than a day will be impossible to skim ( too dry from a pourous backing) browning is less so but you need to be quick and skim the same day. Sand cement 5:1 is great as you have time and can add to or straight edge off till you get it something right and will hold for a skim the following day you need only a five or six foot 2x1 as a straight edge, nice wet mix b.t.w. best way of all by far is to dot and dab dry line with 9.5mm plasterboards and dryline adhesive, you can also beef up the insulation with shelter boards (insulation backed plasterboards) on the external walls.
To be blunt though plastering is not a job to tackle if a complete novice but on the up side dot and dab is d.i.yable and the best way foward.

 

[AndyDavis]

The cement based plaster sounds interesting, especially as theres a bathroom to be done later, is it a lot better than the Gypsum stuff?

I spoke with the Blue circle people and they suggested a two coat method too. Sand:Cement 3:1 for the first coat (10mm) and 5.5:1 for the second coat (10mm), cure after two days and leave for another five days before the second coat. Sounds good but does each coat really need to be 10mm, also they insisted on using sharp sand instead of plastering sand. Why is that?

 

[legs-akimbo]

Sand cement work : If you can do a bit of plastering then apply a first coat and then as it takes up apply the second.. rule it off .. float it.. devil float it ( nails lightly protruding through the float) all in one gauge. leave as is for the bathroom if tiling, on the bedrooms skim the next day in two coats totalling 3mm.
10 to 12mm on scratch and floating coats a must. Not easy to spred with sharp sand without a dash of plasterciser. I would go for 5 sand 1 cement and 1 hydrated lime. Modern materials may be more readily used and practical theese days but to my way of thinking if its tried and tested and it aint gonna fail untill I am long long gone then its good enough for me. In Ireland we dont use browning everything internally is hardwall (sand/cement) 70,000 house construction last year must mean it works