Cementitious article comprising hydrophobic finish

A mat-faced gypsum board comprising:

• (a) cementitious core;
• (b) fibrous mat comprising polymer or mineral fiber, wherein the mat has an inner surface facing at least one face of the gypsum-based core, and an opposite outer surface;
• and
• (c) hydrophobic finish facing the outer surface of the fibrous mat, the finish consisting essentially of:
• (i) hydraulic component comprising Class C fly ash,
• (ii) one or more of the following film-forming polymers:
• acrylic polymers and copolymers, rubber-based polymers and copolymers such as styrene-butadiene rubber, copolymers of styrene and acrylic, copolymers of vinyl acetate and ethylene, copolymers of vinyl chloride and ethylene, copolymers of vinyl acetate and VeoVa (vinyl ester of versatic acid), copolymers of vinyl laurate and ethylene, terpolymers of vinyl acetate, ethylene and methylmethaacrylate, terpolymers of vinyl acetate, ethylene and vinyl laurate, terpolymers of vinyl acetate, ethylene and VeoVa (vinyl ester of versatic acid), and any combination thereof, wherein the film-forming polymer is in an amount from about 5% to about 25% by weight of the wet finish, and
• (iii) alkyl alkoxysilane in an amount from about 0.1% to about 5% by weight of the wet finish.

A mat-faced gypsum board comprising:

• (a) gypsum-based core;
• (b) fibrous mat having an inner surface facing at least one face of the gypsum-based core and an opposite outer surface;
• and
• (c) hydrophobic finish facing the outer surface of the fibrous mat, the finish comprising
• (i) Class C fly ash,
• (ii) film-forming polymer, and
• (iii) silane compound having a molecular weight of at least about 150.

An article comprising:

• cementitious core material;
• and
• finish composition facing the cementitious core, wherein the finish composition comprises Class C fly ash, film-forming polymer, and silane compound of the general formula:
• (RO)3—Si—X,
• where RO is an alkoxy group and X is an organofunctional group.