What do you mean by 'treat'? Are you expecting to leave it uncarpeted? In that case a thick cost of oil-based paint (on primer) is your best bet. Varnish will wear through pretty quickly.Hi I have removed the old carpet from my stairs .The wood underneath is untreated .I have sanded the wood down and filled the edges that connect to the wall/Bannister .What would be best to coat the floor with ? Many thanks John