Preparing To Plaster????

Kelkiwi

I am in the process of stripping the walls in a bedroom as it will need a skim and some patchwork done on some holes, one of the walls is painted straight onto the plaster do I need to strip this off so a skim can be put on or can I just sand it with coarse sandpaper to provide a key for the skim to adhere to?

Cheers

madeane

If the paint is emulsion and in a good, sound condition, it can be plastered straight onto, a skim coat of multi finish plaster will need 1 or 2 coats of diluted PVA glue for it to adhere to the wall. I would only sand it if the paint finish was silk or gloss.

adaze

I think there are ways to "prepare" the walls whatever the paint, could be wrong though. Otherwise I'd agree with madeane.

Kelkiwi

Bump where is Nelly or Jase when you need them? :j

jason_s_2

Hi kel, If the walls have been painted in silk then it is best to give it a bit of a key (ie, sanding),as when the plasterer comes to put the pva on 1, it takes ages to dry and 2, the pva runs down the wall. If its matt,then you should be ok to pva over the top without sanding.

Jase

Kelkiwi

jason_s wrote: »

Hi kel, If the walls have been painted in silk then it is best to give it a bit of a key (ie, sanding),as when the plasterer comes to put the pva on 1, it takes ages to dry and 2, the pva runs down the wall. If its matt,then you should be ok to pva over the top without sanding.

Jase

Jase cheers mate exactly the info answer I was after :beer:

agent_orange_2

My mate who is plasterer, recently skimmed a room for me. He gave me this sort of green coloured paint which had something like sand or grit in it. He asked if I would paint the walls with this stuff. I know it is proper industrial sort of stuff and quite expensive. Could you just put sand in a cheap tin of emulsion for the same effect?
I've had a room skimmed before where the plasterer just used pva.

diamond_dave

Agent orange is correct about the sand - what I do is to give the whole area a coat of PVA then dust the area with fine sand and allow to dry. The sand provides a brilliant key for the plaster. Many times I have been to places where people have just plastered without keying the original surface and the plaster eventually comes off in sheets. If you think about a cement rendered wall which is then skimmed you'll see what I mean.

owls

plastering over paint is bad news if you dont key the surface first.
the green stuff as described is Thistle bond it ,made by the same people as who make the plaster -british gypsum.
its green in colour and the bits as described is silicone sand and is designed so that a skim coat will adhere to the wall correctly, and also kills the suction of the background so it is better to plaster to.

I wouldnt advise just using pva as diamond dave rightly says as the plaster drops of in sheets as ive seen on a number of occassions down the years.

pva is fine if the existing wall is a bit rough, but for a smooth wall you require a key, pva with sand also does the job, but for thirty quid a tub for thistle bond it that will cover a lot of area, a good 50 square meter, why take the gamble.

cargo

I am sorry for this and don't mean to confuse even more.
There is a lot of posts on different forums about this bonding agent (wickes and thistlle brand)
I am a plasterer and have been for the past 25 years.
I have used gallons and gallons of pva over the years, especially the last 10 years as the trend is to skim everything so you can paint the walls.I get my work via recommends (don't advertise).
I have yet to get a phone call saying the skim as fell of in a sheet.I bought a tub of the Wickes stuff a couple of jobs back to check the stuff out.
Impressed with the key it gave and would consider using it on a gloss type finish.
The only other thing a may add is don't use B&Q own brand pva "or if you do" add very little water as it is very weak.

Ps: owls n jas.
I know you guys are in the trade and know what you are talking about and agree with all you say but in my experiance pva is fine for most surfaces.

home_alone

cargo wrote: »

I am sorry for this and don't mean to confuse even more.
There is a lot of posts on different forums about this bonding agent (wickes and thistlle brand)
I am a plasterer and have been for the past 25 years.
I have used gallons and gallons of pva over the years, especially the last 10 years as the trend is to skim everything so you can paint the walls.I get my work via recommends (don't advertise).
I have yet to get a phone call saying the skim as fell of in a sheet.I bought a tub of the Wickes stuff a couple of jobs back to check the stuff out.
Impressed with the key it gave and would consider using it on a gloss type finish.
The only other thing a may add is don't use B&Q own brand pva "or if you do" add very little water as it is very weak.

Ps: owls n jas.
I know you guys are in the trade and know what you are talking about and agree with all you say but in my experiance pva is fine for most surfaces.

agree with you cargo my son has his own plastering firm and swears by wickes pva would not touch B & Q pva.

gary