Clay plaster advice

[goldfinch]

Hello - I'm looking into clay plaster and I had a question about substrates. I like clay plaster for its attractiveness and perhaps to buffer humidity (although I don't know how much difference this will make in the grand scheme with a good ventilation system). Breathability isn't an issue for the ceiling or these walls as they're modern cavity.

The ideal substrate sounds to be wood wool board, at it's meant to give a very good key and work with the clay's moisture buffering. However, for a whole house it's going to get expensive.

Can I clay plaster on to plasterboard? It's meant to be possible with a PVA and sand primer. It would save a lot on my already stretched budget so if it would be fine then it would really help. However, I wondered if plasterboard might absorb moisture but not release it, and so partnering it with heavy clay might not be a good combination. I don't fancy redoing everything if it will start sagging or delaminating because of a poor key.

Thank you for any advice you can give.

 

[jamest]

I can't say that I've ever used clay plaster over plasterboard, but I have lime plastered/skimmed over plasterboard which would seem to raise the same issues. With lime, what I did was to use bluegrit stuff to seal the plasterboard and provide an adequate key for the lime plaster - it's very cheap and seems to work fine and I can't see that it would be any different for clay plasters. The other thing that could be relevant given that you've mentioned 'heavy clay', is that you don't want to exceed the carrying capacity of the plasterboard else the paper will tear off. It would take a pretty thick layer of plaster to exceed this as I think it's in excess of 30kg/sqm.

 

[ContraryMan]

Hello - I'm looking into clay plaster and I had a question about substrates. I like clay plaster for its attractiveness and perhaps to buffer humidity (although I don't know how much difference this will make in the grand scheme with a good ventilation system). Breathability isn't an issue for the ceiling or these walls as they're modern cavity.

The ideal substrate sounds to be wood wool board, at it's meant to give a very good key and work with the clay's moisture buffering. However, for a whole house it's going to get expensive.

Can I clay plaster on to plasterboard? It's meant to be possible with a PVA and sand primer. It would save a lot on my already stretched budget so if it would be fine then it would really help. However, I wondered if plasterboard might absorb moisture but not release it, and so partnering it with heavy clay might not be a good combination. I don't fancy redoing everything if it will start sagging or delaminating because of a poor key.

Thank you for any advice you can give.

Clay Boards are available and you can definitely skim clay onto these.
I am thinking of using them on my ceilings when I get round to insulating walls with woodfibre and all lime skimmed.
Need to look into clay for the bathroom.