An emulsion comprising water as the continuous phase, a wax as the discontinuous phase, an emulsifier and a preservative having the general structure: ##STR00001## wherein R.sup.1 can be a heterocycle containing nitrogen and sulfur, such as thiazolyl, isothiazolyl, or thiadiazolyl, which can optionally be substituted with C.sub.1 C.sub.6 alkyl; R.sup.2 can be hydrogen or C.sub.1 C.sub.6 alkyl, specifically hydrogen; n is 0, 1, 2, or 3; each instance of R.sup.3 can independently be hydrogen, C.sub.1 C.sub.6 alkyl, phenoxy, C.sub.1 C.sub.6 alkoxy, halo, amino, C.sub.1 C.sub.6 alkylamino, di C.sub.1 C.sub.6 alkyl amino, imidazolyl, thiazolyl, isothiazolyl, thiadiazolyl, thienyl, furyl, pyrryl, naphthyl, phenyl, halophenyl, C.sub.1 C.sub.6 alkyl phenyl, or C.sub.1 C.sub.6 alkoxyphenyl. The preservative may be added to the emulsion after the emulsion is formed. The emulsion can be incorporated into a gypsum product such as gypsum board or gypsum wood fiber board. The gypsum product may be made by forming a slurry containing gypsum, water, and the emulsion into a solid product. A method for improving the water resistance of a lignocellulosic composite product prepared by mixing lignocellulosic material with a binder to form a mixture and solidifying the mixture in a selected configuration to form the composite product may include adding to the mixture an emulsion as described above.