Yes, varnishing should enhance seems. Have you ever considered to use Oil: Linseed or Flaxseed, Danish will do? Oil requires significant drying time compared to wipe and poly, but it gives a different effect to the wood (not to mention Oil protects timber).Thanks for the tip. That cross my mind, but makes me very nervous. I think I'll experiment on some scrap wood before I dig into the deck. I haven't applied any finish yet (intend to apply wipe on poly). Would that enhance seams between planks?