<p>A method of introducing boron as a boron ester into timber via a non-aqueous liquid medium. The borate ester may have the formula I: (RO)<SUB>3</SUB>B where Rl may be a C3-C20 alkyl or alkenyl group, R2 may be a C3-C20 alkyl or alkenyl group and R3 may be a C3- C20 alkyl or alkenyl group. The R2 and R3 groups may form of a four or five membered ring structures with diols o aminoalcohols to give completely substituted monomeric borates.</p>
