Sanding is a process which uses abrasive sandpaper to effectively scratch the surface of the wood clean. Within that process there are a number of procedures which follow in certain order, generally starting with rough grit sandpaper (sometimes 24 abrasive pieces per square centimetre) and following through to smooth grit sandpaper (up to 120 on a belt sander) with the aim to clean the floor surface from any previous sealant, indentations, scratches and stains. Sanding takes timber back to its raw, natural state in which almost all wooden species look lighter than they would when sealed.
The equipment used ranges from aggressive large belt sanders, capable of deep sanding and flattening undulations of up to 5mm, to polishing sanders used mostly to achieve a smooth finish immediately before sealing.
The type of sanding performed is almost invariably a question of a judgment on the spot by a trained operative. It would depend mostly on what the previous sealant was and therefore how aggressive the sanding needs to be to clear it. It also will vary according to the general level of the floor and the discrepancies between the individual planks or blocks.
Uneven floors would require the use of a belt sander in order to achieve a flat surface, whereas floors that are level may be sanded with a polishing/cleaning sander.
Older and delicate floors, like Antique floor, although undulated should still be sanding with a polishing sander so as to protect their often brittle edges and to prolong their lives without reducing the thickness.