I Have a small two block high garden wall that is about a meter long. Previous owner slaped interior paint on it so after a couple of years weathering it looks a mess. I was going to just paint over with white sandtex but think it would look better rendered. Wickes do a just add water render mix, but I already have some cemetone just add water Morter. Presumably render mix differs from normal morter I guess more sticky to adhere to the wall. What do I need to add to the morter mix in order to make render? Also can I get away with a single coat?