Methods for rendering a cellulosic substrate hydrophobic include providing a plurality of halosilane compounds comprising at least a first halosilane compound and a second halosilane compound different from the first halosilane compound, wherein the plurality of halosilane compounds comprises a total halosilane concentration comprising 20 mole percent or less of monohalosilanes, 70 mole percent or less of monohalosilanes and dihalosilanes and at least 30 percent of trihalosilanes and tetrahalosilanes, and, treating the cellulosic substrate with the plurality of halosilane compounds, wherein the plurality of halosilane compounds are applied as one or more liquids.