This invention relates to a timber preservative solution, to a method of treating timber using the preservative solution and to timber so treated. Boron based timber preservatives are common in the art. However, the ability of boron to diffuse in this manner results in a commensurate propensity to leach from the timber fairly quickly. The timber preserving solution comprises a timber preserving water soluble inorganic salt solute, such as boric acid, borax, boric oxides or, preferably, Disodium Octaborate Tetrahydrate (D.O.T.), dissolved in an aqueous polymer solvent, such as commercially available aqueous polymer products. The boron compound is preferably mixed with the aqueous polymer solvent in a range of concentrations of from about 20 g/l BAE (boric acid equivalent) to about 300 g/l BAE.