Floor board comprising a decorative surface layer applied to a substrate, wherein said substrate comprises MDF or HDF material at a side edge thereof, wherein said side edge is treated with a sealing agent; wherein the sealing agent is based on a superabsorbing material, said superabsorbing material comprising crystals of polyacrylate, or the sealing agent relates to particles of bentonite clay, amorphous silica or fuller earth, such as palygorskite and/or attapulgite.