Disclosed herein is a preservative formulation for use in treating wood or other cellulosic materials, said formulation comprising: at least one biocidal metal compound at least one preservative and an aqueous carrier, wherein the preservative formulation has an uptake in the sapwood of less than about 220 L/m3 yet achieves substantially full penetration of the sapwood. In a preferred embodiment, the preservative formulation is copper/tebuconazole in a ratio of about 25/1 w/w. The treatment is suitable for wood less than 25 mm in thickness and is suitable for residential applications such as decking.
