Some advice please. I am about to decorate the outside walls of my bungalow and it is part brick to window cill level and rendered above. On the south facing side there are a number of cracks in the render which follow the line of the blockwork under the render. It is not major, but what is the best way of making good the surface before repainting. Do I have to rake out and paint PVA to the exposed surface, and what sort of mix should I use?