Render over Damp Proof Course in Pre WW2 Bungalow


Postby ChrisTB » Wed Oct 21, 2015 3:18 pm

This pre WW2 bungalow has all exterior walls rendered -smoothed sand and cement. This old rendering is taken over and below the dpc of the outer skin of the wall. It is now cracked and I am concerned that moisture can now track up the walls and may be the cause of damp within the bungalow. The cavity has, at some time, been filled with blown in insulation. I have re-rendered one wall sealing the slate dpc with a suitable mastic and fitted a bell shaped stainless steal trim along the line of the dpc making (I hope!) a barrier to damp rising through the render. I also added a waterproofing additive to the second coat of render.
Any thoughts please on the wisdom of this before I do any other walls.
Thanks.
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Postby rap12 » Sat Oct 24, 2015 2:04 pm

The waterproof additive is mixed in the water of the first coat.

You dont "seal" DPC's with mastic.

Blown with what kind of cav insulation?

Cav insulation can cause endless damp difficulties - do you actually have any interior damp signs?
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Postby ChrisTB » Tue Oct 27, 2015 11:52 am

Thanks for your reply. Right, I didn't "seal" the dpc (sorry - wrong word!) I raked out the loose mortar above and below the dpc and filled the gap left with mastic. The cavity wall insulation is, I believe, blown mineral wool and the only damp within the bungalow at present is caused by condensation which we control. Why add waterproofing to the first coat of render? Wouldn't this stop the second coat from adhering properly and wouldn't rain penetrate the second coat?. The wall I treated now seems to be dry. Comments much appreciated.
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