Water-resistant gypsum compositions and emulsion for making same

A gypsum composition settable by hydration to form a water-resistant gypsum product comprising a mixture of:

• a) 100 parts by weight of gypsum, and
• b) 0.5 to 20 parts, by weight, of emulsion solids, per 100 parts, by weight, of gypsum, of an aqueous emulsion comprising water and:
• i) a paraffin hydrocarbon having a melting point of 40.degree.-80.degree. C.,
• ii) montan wax in an amount of about 1 to 200 parts, by weight, per 100 parts of said paraffin hydrocarbon, and
• iii) polyvinyl alcohol in an amount of about 1 to 50 parts, by weight, per 100 parts of said paraffin hydrocarbon.

A method of manufacturing a water-resistant gypsum board comprising:

• I) forming a mixture of:
• a) 100 parts by weight of gypsum, and
• b) 0.5 to 20 parts, by weight, of emulsion solids, per 100 parts, by weight, of the gypsum, of an aqueous emulsion comprising water and:
• i) a paraffin hydrocarbon having a melting point of 40.degree.-80.degree. C.,
• ii) montan wax in an amount of about 1 to 200 parts, by weight, per 100 parts of said paraffin hydrocarbon,
• iii) polyvinyl alcohol in an amount of about 1 to 50 parts, by weight, per 100 parts of said paraffin hydro carbon,
• II) forming a layer of said mixture on a first liner,
• III) disposing a second liner on said layer in opposed relationship with said first liner to form an assembly of said liners with said layer sandwiched therebetween, and
• IV) drying said assembly while permitting hydration of said gypsum, to form said board.