I need to do a small patch to a roughcast wall. I have done quite a bit of searching on the web and there has been a lot of advice. I just want to make sure that I am doing the right thing. The patch should consist of two layers 1) a scratch coat (3 sharp sand: 1 cement + waterproofer) 2) the rough cast coat (4 sharp sand: 1 cement +waterproofer? + 6-10mm chips Wet the wall and the put on the scratch coat. 10mm thickness maximum. As it gets drier scratch some horizontal lines in it. Let it dry out. Can I use any kind of 6-10mm chips for the rough cast coat or do they have to be lime chips? What proportion of chips should I use in the mix? Do I need waterproofer in the roughcast coat? Wet the scratch coat and put on the roughcast coat. Does this sound correct?