Most 3/4” floors can be sanded 3-5 times depending on how aggressive each sanding is. Almost every site finished floor is sanded immediately after being installed which counts toward one of the sandings it can handle. Indicators that a floor has become thin are exposed nail heads that used to be covered by the top of the tongue and groove system, splintering, creaking, and gapping. Once the flooring becomes thin, any repairs needed become difficult or futile. That’s because replacing a split or stained board in a 1/4” floor with new 3/4” board will require that new board to be sanded to the same thickness in order to be flush. Doing so will essentially ruin the new board and the process may damage boards around it beyond repair. Sometimes it still makes sense to sand a thin floor but clients must understand that doing so will likely cause additional splintering, increased squeaking, as well as exposing nail heads Exposed nail heads can oxidize and cause staining when using water based finish or water popping for stain. If we feel a floor is too thin to sand we will let you know.