Switching to 80

When to switch grits? First, a great filler is 3M platinum select. I do more blocking with 80 grit than anything. I just get the rough shape in the filler with 36 grit before it's dry. Once it's drier, I switch to 80 grit, and do all the fine tuning. With the right filler, 80 grit cuts the filler great, and you won't have deep scratches left over from the 36 or 40 grit. Also, 80 grit gets the filler a lot more dialed in than 36 or 40 grit does.