Sand and Cementing Internal walls of old properties.

9 May 2015
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United Kingdom
My older property is plastered inside and out with lime plaster.

I need to replaster large cubboard in Kitchen with one external wall and 2 internal walls.

The lime render of the exterior of the property is in good condition and my flat has never suffered from damp.

My preferred method of replastering this cubboard is using sand and cement with added waterproof throughout with a finishing plaster on top.

My reasoning is that the external render is doing the job and the property is able to breathe externally. So the sand and cement will seal and waterproof the brickwork internally. The external wall will only therefore be able to breath in one direction only but this should be enough to keep the wall dry.

My question is does my reasoning hold true? Can a wall breathe in one direction only and keep in good condition?

Thanks for any time you can give to this.
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Speaking as a non-expert here...
Normally you'd use lime putty plaster for this, which would be my preference, partly because I find it so easy to use and you can store excess forever. I found Heatree's book The Damp House useful to get my head around things - he talks about walls as being a device to move moisture outwards from the house (it took me a while to get my head around that!). If I remember correctly he recommends a porosity gradient going up as you move outwards through the wall, so that moisture isn't getting into the wall from the room and getting trapped there. So you're better off having any (low porose) cement on the inside than on the outside. I certainly wouldn't add any waterproof though - if you're not going to use lime putty then I would suggest NHL 2 hydraulic lime (use it just like cement).
Lime plaster can also (in theory) regulate the humidity in the room - absorbing water at times of high humidity and releasing them at times of high dryness.
Hopefully you'll also get some replies from actual tradespeople who know what they're talking about!

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