Provided herein are an aqueous wax emulsion, comprising water; a paraffinic hydrocarbon; polyvinyl alcohol and a wax component comprising synthetic olefin wax component. The synthetic olefin wax component may be selected from the group consisting of (i) a synthetic normal .alpha.-olefin wax; (ii) a synthetic olefin wax of a carbon chain length of about 20 or more carbon atoms, that is modified by oxidizing and/or by refining through distillation or stripping; and (iii) combinations thereof. Such emulsions are also useful for and disclosed herein are settable gypsum compositions and water-resistant wallboard formed therefrom. Also included herein is a montan wax substitute for use in an aqueous montan-based wax emulsion having paraffinic hydrocarbon, a wax component, water and polyvinyl alcohol wherein the wax component includes the montan wax substitute in place of use of a montan wax in the wax component such that the montan wax substitute is about 1 part to about 100 percent of the wax component and includes a synthetic olefin wax.