Whitewashed hardwood floors look better if they are sanded before the application of stain, sealer, or polyurethane. This is because sanding creates and exposes the cracks in the surface of the flooring planks. These pores are filled properly when stain is applied. This helps in deeper absorption of the stain to create a perfect look. If the floor is sanded after the application of stain, during the sanding there is a chance that the stain would get ruptured and cracked from different points. Also, the appearance of the floor plank that is whitewashed, would not be balanced.