Compositions and methods are provided for treating products containing wood fibers to provide protection against wood destroying organisms and fire, and resistance against leaching of the preservative from the wood fibers by water in exposed environments such as exterior applications. The methods involve applying to a substrate an aqueous preservative composition containing a boron compound, a source of zinc, an aqueous silicate, a source of alkalinity, and an amino acid. The compositions may be applied by vacuum and/or pressure treatment or dip treatment under atmospheric pressure.