The present disclosure relates to a wood preservative formulation comprising a biocidal agent which is a copper or zinc ion complexed with an amino compound selected from the group consisting of ammonia, a water soluble amine or aikanoiamine and an aminocarboxyiic acid and a cationic polymer, as well as to aqueous treatment solutions comprising such a formulation and methods of treating wood or other cellulosic material utilising said formulation. Examples of a cationic polymer include compounds of formula (I), (II) and (III).
