I'm about to have a go at rendering the outside wall of a new extension, I've built. I've had a look at my local builders merchant and they have 3 different sands in stock. Building sand -- very smooth texture. Plastering sand-- slightly gritty and sharp sand--very gritty. Which sand do I use or do you mix them. Thanks for any information
for areas of extreme exposure i'd suggest using a sharp sand mortar,
you can blend these with other sand but generally the coarser the mix the better. The render should be about 20mm thick and be applied in two coats. Also remember to put a bell-drip at dpc level to kick away water from wall.
A bell drip also known as Render Stop Bead forms and protects the lower edge of external render. It is designed to deliver a gentle gradient at the base of the render, it is used above doors, windows and at DPC level to allow rainwater to drain clear of the underlying substrate.