This was a 1/2" thick quartersawn white oak floor that had been sanded at least once before. This doesn't leave much thickness of wear layer and we were worried we'd sand "down to the nails". We were also worried about using a waterborne finish system here because it can sometimes cause even 3/4" flooring to warp or "edge curl", so this floor was finished with Bona's oil drifast sealer and topped with Poloplaz's satin Primero oil-modified urethane, 4 coats in all. As long as they keep up on maintenance and have this floor coated periodically (every 5-10 years) before any spots wear out this should be the last time this floor ever gets sanded.