I have a rather large deck area to the side of my apartment...Last year on the advice of a carpenter (duh!) I painted the deck (as it had been untreated) with a wood paint product recommended for fences. Carpenter said it should be fine....As it happens its not fine..During the winter when the deck was wet the surface was dangerously slippy and the finish was unsatisfactory...So it needs to be repainted. Question is do I need to sand it back first to get rid of the stuff I painted it with or will it be ok if I simply use an appropriate deck treatment product? I painted it with a Ronseal wood product recommended for fences.