I am just about to take on the task of rendering the outside of my house. I have good knowledge of plastering but just wondered on the mix and what additive i should put in. i been told by the lad in the local builders merchants to use 4 parts sharp sand, one part cement and a bit of Renda mix (from screw fix)is that correct. Also what do i need to put around the windows, doors and the top of the engineering bricks where the render is going to stop. If anybody can help please reply!!!!!!!!!!!