Plaster types

[Anonymous]

Hi - this is probably going to sound like a very stupid question but I'm new to this whole renovation lark so be gentle with me!

I've been reading all these posts and also in other places about not using normal plaster on an old house as this encourages damp and is generally not good for the house. We have a georgian (non-listed) semi-detached that has a lower ground floor. The plaster on the lower ground floor is very crumbly but in the rest of the house it's fine. I know we're going to have to do some replastering in the next few weeks (as we're taking the roof off) but I don't know how to work out what kind of plaster is up there at the moment. Is there a way of telling whether it's the right or wrong stuff on the walls already?

Also does painting the right kind of plaster with the wrong kind of paint (ie modern emulsion) defeat the object of having the right plaster?

We are using family to do the work (who know what they're doing in the most part but maybe not on a house this old!) and I want to make sure we don't do anything wrong!

Would really appreciate any advice. Many thanks

Rhian

 

[Anonymous]

If the plaster you've got is very crumbly, chances are that it's lime plaster. If you can see little white bits in it, and bits of hair, that makes it more likely to be lime plaster.
If it's pink it's Spam.
Sorry, kneejerk reaction - if it's pink it's more than likely to be a modern gypsum-based plaster. If it's as hard as concrete and doesn't crumble, then it's certainly gypsum-based.
As for repairs, you should try to use like for like; so a lime plaster for repairing a Georgian house. And if you hire a plasterer, make sure he knows how to use lime - very few of them do. If you do it yourself (en famille), prepare for a learning curve that's initially steep but good fun, and welcome to the addictive world of house husbandry.
And as for finishes, ideally you should use a breathable paint, but if you have no signs of damp and it's an internal wall, you could probably cut corners and get away with a modern paint. The plaster won't be able to breathe, but it should still flex and be as tolerant to movement.
Speaking personally, I'd use a breathable paint like a distemper, but if you've got young children and heavy traffic through the room in question I can see the case for washable paint!

 

[Anonymous]

Thank you Gervase - that really helps! the books all tell me what I should be using but doesn't say how to recognise what's already there! I think it does sound like lime but I'll have a good poke around this weekend to be sure.

We will definitely be taking off the emulsion and use a distemper but good to know that if we use emulsion as a temporary measure it's not going to do any harm... especially as that is clearly what has been used for at least the 50 years!

 

[Anonymous]

Original plaster would normally be lime, which is nearly always white. Lime plaster has a long open time, whereas gypsum is short and you have to work quick.

A minority of housing has mud/clay plaster, dark brown.

Theres not much likelihood of it being anything else originally.

Distemper can be washed a few times gently with cold water, but use hot and it comes off. YMMV though as there are different types of distemper.

Emulsion can be washed lots of times. If the wall has been fine for 50 years with emulsion, its not likely it would sudenly become a problem. But if you want original character, distemper has a softer and pleasant character, as well as allowing any slight dampness to evaporate. It is also very cheap to make.

Purists cover your ears now. Distemper and emulsion can be mixed, I did this once to get the right colour. If mixing, note that distemper changes colour as it dries, emulsion doesnt.

NT