miah said:
For out side plastering do you just simply use sand&cement?
NO !!
Outside rendering mix consists of 5 parts Washed sand to 1 part cement and 1 part hydrolised LIME.
The use of lime allows render to breathe slightly, which reduces the possibility of cracking. It also enables a better float or sponge finish.
The use of lime is also incorporated in the mix for pebble, and wet dash though considerably more in the latter.
On occasion I have used washed sand and compo' ( Flooring sand) roughly 50/50 together with 1 cement and lime, as a scratch coat, to obtain a solid base for the fining coat ... especially where ornamental moulds are to be run afterwards.
It seems the biggest problem is the misconception that more cement makes for stronger render ... where the truth is it makes bigger cracks and causes separation between the wall surface and the render.