Roughcast rendering

[nielsc]

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?

 

[Moz]

That sounds ok to me ,

yes use lime chips...

 

[nielsc]

Thanks Moz.

I think I will go ahead now.

Will put waterproofer in both coats, better safe than sorry.

 

[JohnD]

If you are doong a patch, I take it a small section in an existing wall? it can be difficult to get a match, but if you sweep under the old wall you will probably find plenty of the stones or chippings that were used before and have fallen off. You might be able to incorporate them in the final layer.