Interior render: lime mortar or waterproofed cement mortar?

Postby Gingerirvin » Fri Jan 28, 2011 10:06 pm

I've got a stone built house without any damproofing. In the ground floor room I'm doing up the walls are plastered with a cement based render, the bottom 750mm of which has been made powdery and weak due to damp and there's lot's of efflorescence. I intend to hack this 750mm strip off, rake out the joints and reapply... what? The room has concrete floors which are bone dry despite the lack of DPM. There is no heating at present, though when I knock through it will be heated by a wood burning stove. The damp in the walls isn't great at all despite the condition of the existing render.

Option 1: I've got some bags of St. Astier hydraulic lime (powder). I've mixed this 1:2 (lime:sharp sand) and applied 2 coats to interior 1st floor walls with surprising ease and with pleasing results. Is this a good option for the ground floor? Can I apply a masonary paint over the lime or should I decorate with a specialist breathable paint?

Option 2: Cement based render with waterproofing admixture.

Which option should I go for? Is there a third more suitable option? Cheers.
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Simply Build It

Postby stoneyboy » Sun Jan 30, 2011 8:45 pm

If there are lots of cracks in the existing render replacing it with the same again will end with the same result.
You could try the lime mortar option but you will need to add some binding eg horsehair and the wall must be able to breath.
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Postby Gingerirvin » Sun Jan 30, 2011 10:38 pm

Thanks for the advice. There are no cracks. My gut feeling was the lime render. So that's what I'll use. A friend has given me a recipe for distemper today, so I reckon there will be no problems re the wall breathing with a finish of that. Cheers.
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