What to plaster my walls with?

Mostly just checking - I tend to get quite nervous when embarking on the next job.

I have quite a bit of plastering to do onto bear rubble/mud built walls. They did have a layer of mud and straw covered with lime plaster, but the mud and straw daub has given up adhering to the walls. I'm left with very rough walls, which present about 1/3rd mud facing, which isn't particularly strong. Unless someone stops me, I'm going to apply a 1:2.5 mix of Castle hydraulic lime and "plastering sand".

I am toying with the idea of spraying the walls with some pva fist?

If it all goes horribly wrong, what's the best type of plaster to use?

T
Reply to
tom.harrigan
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If it's mud wall then I'd expect you to need a breathable plaster such as lime

AWEM

Reply to
Andrew Mawson

rubble and mud walls? - the house must be 500 years old? - isn't there a preservation order on it?

If there is only a room or two to do, and assuming you want to preserve the walls intact for posterity, this would be my plan of attack:

vapour barrier entire wall(s) build studding tight up to wall(s) insulate with fibreglass plasterboard and skim

this makes for a warmer, straighter and condensation free wall, and if needs be, in the future you can take down the stud walls and there are the mud/rubble walls intact.

I don't think sand & lime will stick to mud

Reply to
Phil L

No I dont think thats a good idea

I find it interesting that straighter is considered to be an advantage. You are not the only person to think so - straight walls have been desired since the neoclassical revival of c1780 but before then people didnt think straightness important. In an old house which originally had no pretensions to classicism it is more characterful and of its time if the walls wander around a bit and you aim for continuous but not straight walls (easier to DIY too)

Yes that would work I expect, I have never tried but it counts as a good conservation method if it leaves the walls intact

Yes it will. My house is just that. Well no its clay not mud but I expect thats what the OP has too. So long as the clay is dry it will be fine

Dont make the common mistake that strong = good

The rule to follow is that each layer should be weaker than the one underneath. Your daub wall is not strong so whatever goes on to it should be as weak as possible so if you decide to use lime then use the weakest lime mortar you can get which is lime putty mortar not hydraulic lime mortar

Any daub which is actually falling off can be removed first but dont go poking around to see if any more will come away because it all will. If you want to be economical of lime and time* then mix up some more daub and use it to level up the walls not forgetting to scratch the surface to give the lime mortar a good key

  • Daub just dries so you can blast heat at it if you want to dry it PDQ. Lime has to be built up in 10mm layers and each layer has to set before you add the next. To be on the safe side leave 3 weeks between layers

Dont forget to damp down the wall before adding the next layer

Lime needs CO2 and water to set so keep the room cool/warm (not hot - water will evaporate, not cold - it will take forever to set) and add a fan heater to blow the air around

Anna

Reply to
Anna Kettle

It sounds like the OP could really do with doing some basic reading on historic properties before doing anything. Maybe ask on the

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forum.

NT

Reply to
meow2222

Any particular reason?

It has stuck, and the walls have no clay in them. The "mortar" is in fact the local subsoil.

What do you mean by "strong"?

Unfortunately the original builders didn't take your advice and put a weak, soft, topsoil+straw mixture on before the relatively "strong" lime plaster.

Where does one get daub from, and how do you mix it into a consistency that is both workable and will produce a durable layer? Are you suggesting I dig up my garden?

Alternatively a cement render will do a perfect job in a fraction of the time for a fraction of the price. There are sections of wall that have been repaired that way, and they are in perfect condition.

Your clients are obviously the sort who have an excess of money and patience. Unfortunately, I'm just an average person with the usual time and financial constraints.

In all the excitement I did forget to dampen the first area of wall I rendered. It did result in a few cracks, but they just close up with a trowel. Dampening the other areas didn't make any difference.

Very impressive! Your amazing work would look totally out of place in my house though...

T
Reply to
tom.harrigan

Not a good idea: in the winter the VB is on the cold side of the insulation and you'll get condensation on its inside surface rotting the new studwork. In summer if the outside wall gets a soaking in a shower and then the sun comes out you could get condensation of the outside surface of the VB, rotting the old wall.

Reply to
Andy Wade

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