36-grit is, hands-down, the most commonly used grit in floor sanding. In our entire time in the floor sander rental business, we have never seen anyone sand an old, finished floor without it.
Many customers test a small spot on their floor with a palm sander and 60-grit and make a little spot of bare wood, then they come in and insist that they can start at 60-grit on the drum sander. It sounds reasonable, but it never works when they scale up to the big sander – over the larger areas that drum sanders must cover, even small amounts of finish cause 60-grit to glaze over quickly.
And 60 grit is not strong enough to sand down the high spots in the wood. 36-grit is your friend because it sands wood fiber like the biggest boss. 36 grit is also calibrated to soften scratches from any 24 grit sanding that may have come before it. 36 grit doesn't remove 24 grit scratch completely; it shrinks it down and gets it ready to 60 grit to do her magic.
If you floor is newer with a thinner finish, sometimes you can start with just this grit. Many brand-new, bare floors need to start sanding at this grit because the lippage or overwood from board to board takes a coarse grit to make it level. Just about every rental customer leaves the store with 36-grit, and they rarely bring it back.
Allow one belt for every 250-300sqft
Silicon Carbide mineral