We have started seeing staining on the k rend that's running off the end of the window sills, new upvc windows, 150mm sills, render is a cracking job, someone has mentioned that we could have upstand put on the sills, what exactly do they mean in upstands, I was thinking of just running a bead of silicone along the upper outside edges of the sills to channel any rain run off to the front of the sill, what's people's thoughts cheers