Phil Addison wrote:
I [ ... ] have bought a bag of lime, one of Ordinary Portland
Cement, and a couple of bags of sand. I propose to mix 1:1:6
by volume (OPC:Lime:Sand) with no waterproof additive.

To late now, except for discussion, but why no waterproofer?


I'll use this to point and then go straight on to a render
scratch coat, and finish off next day (or maybe the one after)
with a skim of Thistle Finish if I can find some, otherwise
multi-finish. The standard bags of lime and cement are, I am
pretty sure, far more than i need for this 4x2 patch, though
it is quite deep in places, up to 1.5".

If damp penetrates your internal render, you will gey problems
with the plaster. Damp and gypsum plasters don't mix!


J.B.