preparing walls for plaster

[benpost]

hi just thought id update anyone whos interested on my kitchen. after removing all the tiles i was left with half plaster/ half sand render (dusty). i have spoken to my plasterer and he has advised on what i can do to help him. he has suggested removing any remaining loose plaster and then vacuuming the walls for dust. then mixing up half and half water/pva and applying to the render with a roller so it soaks in and absorbs the sand dust. this should dry quickly then i need to paint a coat of vinyl silk white paint on top. finally apply a coat of neat pva to the walls and ceiling. this should leave the room ready for a final smooth coat of plaster. i will be buying all the stuff and starting tomorrow hopefully get that done in 2 days. just wondered if anyone has any tips as i am very much a diy novice. thanks

[Lobster]

Ben, we're all fascinated... ;-)

I'd go along with all that so far, although would go for more dilute PVA (1:4)

Don't know what all that lot's for - sounds odd to me. Any plasterer I've ever seen working (including any efforts I've done myself) will slap on the dilute PVA then go for it.

David

[Andrew Gabriel]

The painting advice is very strange -- not all paints will stick to a layer of PVA, particularly such a strong PVA mix, which might compromise the bond of the plaster to the new wall. I would double check that.

The advice regarding two coats of PVA is normal, except it's usually diluted more in both cases, and the second one is applied immediately prior to the plaster so it's not completely dry when the plaster is applied. Typically first coat diulted 5:1 so it soaks in to the wall easily, stabilising any remaining dust, and second coat 3:1.

Also can't help thinking he's taking the piss regarding putting it on with a roller -- you'll end up with it everywhere! It's usually applied with a giant distemper/wallpaper brush. Protect the floor from drips.

When diluting PVA, start with the neat PVA and add a tiny amount of water initially and mix until smooth. Repeat again. Finally when it's runny you can ditute down to required concentration. If you put all the water in at once, it's very difficult to mix, and you just get gobs of it floating in clear water. You can buy it ready-diluted and tradesmen whose time is money do, but that's much more expensive if your time is not costed.

[The Natural Philosopher]

I'd agree with all except the vinyl silk paint.

And question the need for a second coat of PVA.

Or the vacuuming bit.

In short i'd slop PVA on all the loose stuff and leave it, and do another coat where it was still crummy.

Then plaster away.

But the extra steps won't do any harm.

[George]

i want to do something similar with the crumbly plaster all over this new old house but can i slap on dilute pva to stablilise the dust ant then leave it for a few months (or years) and only replaster it when i've worked out where the wiring goes etc..

or should i slap on some emulsion?

i want to stop the brick dust in the kitchen soonish.

george

[benpost]

hi thanks for the replies. the advice was to use the diluted pva first which will soak into the wall and settle the dust. then paint next, in order to stop the wall sucking all the moisture from the plaster. he specified good quality vinyl paint, instead of matt. then the neat pva coat to level the surface, as the existing plaster is raised compared to the sand render. i wasnt sure about using a roller either, although the floor isnt a problem as i'm going to replace it once the ceilings and walls are done. no doubt i will be posting about the floor soon...

[mail]

Forget the paint Use SBR in accordance with the instruction on wall and in mix in preference to PVA Chris

[benpost]

what is SBR? never heard of it. i've got the stuff now and i'll let you know how it goes. i'm going to follow his instructions as he will be doing the final plaster so keep him happy. thanks for the posts

[Lobster]

Well do ask him what purpose he considers all the extra steps are for, and let us know! (as it seems pretty unanimous here that they are at best unecessary and at worst harmful).

I'll bet he wouldn't be doing all that if he didn't have you doing it for him - he never be able to compete on price for all the time it will take.

David

[Stuart Noble]

It's a rubbery resin used in tanking cellars and in some self levelling screeds. Totally OTT for reducing suction I would have thought.

[Andrew Gabriel]

It's more waterproof than PVA, and used instead of PVA in mortars which will be subject to frequent immersion. It doesn't work quite as well as PVA, so it's normally only used where its more waterproof properties are required. That's pointless with plaster as plaster is somewhat water soluable anyway.

[benpost]

an update: the kitchen has now been fully plastered, i think he had a bit of a nightmare as the walls weren't very good. there was an area where the old plaster was very thick. he used 4 coats on one wall. anyway pleased with the result and while its drying i need to decide on a kitchen... i'll start a new thread..

[sm_jamieson]

Should be within a plasterers normal remit. Did he look at the job first ? Plasterers I have had always pop round and give a price beforehand. If much undercoating, they sometimes they may come back another day. But generally, I have done the undercoating and they just do the skim. Simon.