sand and cement render on top of finish plaster

[Albumen]

in my bathroom I'm rendering around the bath/shower area.

Too complicated to explain, but there's a small section, a 3 inch wide strip about 4 feet long, where I'll need to put a thin coat of sand and cement on top of some finish plaster. It'll have homelux membrane, then tiles, on top of it eventually.

Do I need to PVA the plaster or anything?

Thanks

 

[troweladdict]

oooow can you not just knock it out and float it up iv never tryed to render over plaster maybee if you WBA THE NIGHT BEFORE or can you not just float up to it then use bonding over the plaster

 

[Albumen]

Bit complicated, but the narrow strip of plaster is right at a window corner, so if I take it off I'll end up messing up the angle bead. But it turns in a bit along the wall I'm rendering, so the reason for the thin layer of s/c is to bring that wall square.

If that makes any kind of sense.

I guess I could actually do it in sand and cement to get that wall square, then once it's firm just scrape that thin coat of s/c that's on top of the plaster off, then skim it later.

 

[troweladdict]

id just do it proper m8te knock it off set a new bead in place render it up and skim as you want m8te can you not use tile backer board m8te

 

[Richard C]

How thick is a thin coat? I don’t fancy the idea of render over Finish either; at best you could get reaction problems between the cement & Gypsum unless you prime & at worst it may not stick well at all. I would not advise Bonding or other base plasters either; it's not suitable as a tile base & I'm not sure how the Homelux membrane will take to it either.

Your going to need a highly modified cement powder based adhesive for fixing the membrane anyway;
http://www.bal-adhesives.co.uk/products/rapidset
so just use some of the addy as a render to fill out before applying the membrane.

If not something like this but it’s expensive;
http://www.bal-adhesives.co.uk/products/quickset-render

You must prime plaster or plaster board before using cement based addy.

 

[roy c]

Don't render over plaster for a start, I would "score" up the plaster and get some good quality tile adhesive and bring it out with tile off-cuts ,then use that as your starting base

 

[Albumen]

It's goes from about 4mm to nothing.

 

[Richard C]

Use powder cement tile addy as I said, you need it anyway for the Homelux membrane; you can use bits of tile to pack the deeper bits out but prime the Gypsum or you could get a reaction.

 

[Albumen]

Prime with PVA?

 

[Richard C]

Prime with PVA?

NOOOOO not with cement based addy.

 

[Richard C]

Sorry, should have added use an Acrylic APD primer for cement over Gypsum

 

[roy c]

Your talking about" 4mm to nothing "

 

[Richard C]

Your talking about" 4mm to nothing "

So it does; misread as 40mm ; no need for the tile bits then I'll blame you for that bit roy

4mm is all but nothing; just put an extra layer of addy to fill it out & then apply the Homelux as per.