On 21 Jun 2004 00:38:51 GMT, (Andrew
Gabriel) wrote:

Cement goes back to roman times. However, prior to Portland cement,
it was more expensive, so it wasn't used for everything like it is
today.

Thanks Andrew for clearing that up. I haven't been able to get up there
on a ladder yet to have a closer look, but last time the sill material
looked pretty recent.

I think the only way the sill will be letting water in is if
there are cracks in the render.

If it IS rendered like yours!

If you stop the water entry and let it all dry out, you can use
pretty much anything (personally, I use bonding coat as the scratch
coat). However, none of the gypsom-based plasters are suitable if
it's damp.

I understand why you can't use these if it is permanently damp, but do
you mean you can't use them if there is still residual damp that is
expected to dry out through the plaster. In other words must it be
completely dry before using plaster as scratch coat?

Is that why cement render often seem to be used after damp treatment, so
that it can be applied straightaway to the still wet brickwork?

I have done a scratch (base) coat of cement (and lime if you like it)
and sand in a 1:1:6 ratio, with waterproofer added. Follow up 24 hours
later with regular plaster finish coat (no PVA required unless you
leave it much longer and the scratch coat has dried). The sand and
cement is very effective at keeping the water away from the plaster
finish coat. However, you'll probably need to let the wall dry out
first, at least so it doesn't feel and look wet.

Are you saying if it is not totally dry I should use that sand and
cement mix rather than bonding plaster as the scratch coat? What is the
problem if it is too wet; won't stick I suppose?

Phil
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