After the first part of the sanding. I made two big mistakes kere. 1. I sanded across the grain. The score marks showed- and they would have been better going with the grain 2. The floor was laready fairly level- but I started sanding with the coarsest grain sandpaper ("P40")- which was not only rough- it was brittle. I went through 5 sheets sanding just half the floor in one room (at $5 a pop, al of them just broken)- before being completely successful at the next grade ("p80") and not breaking any of them.