Unlike sanding furniture smoother is not always better when sanding an exterior deck surface. For sanding a deck floor board surface, use a sanding grit of about 60 to 80. For sanding a handrail, use a grit of 80 to 100. Do not use higher than 100 grit. Higher grits of sandpaper will smooth the wood too much begin to close down the pores and may reduce the absorption of the stain or sealer into the wood pores. Use medium pressure on the hand sander checking for evenness of appearance as you go.