Methods for making gypsum boards with polymer coating and gypsum boards made by the method

A method of making a gypsum board, comprising:

• providing a face paper sheet having an inner bond surface and an outer surface and a face paper sheet thickness, the face paper sheet inner bond surface opposed to the face paper sheet outer surface;
• applying a polymer coating to the inner bond surface of the face paper sheet, wherein the polymer coating comprises water and latex polymer selected from the group consisting of acrylics, styrene acrylics, acrylic esters, vinyl acrylics, vinyl chloride acrylic, styrene acetate acrylics, ethylene polyvinyl acetate, polyvinyl acetate, styrene butadiene, and combinations thereof and surfactant, the latex polymer having a glass transition temperature (Tg) of 10° C. to 20° C.;
• depositing a first layer of relatively dense gypsum slurry comprising water and calcium sulfate hemihydrate directly on the polymer coated inner bond surface of the face paper sheet to form a first layer of relatively dense slurry, wherein all of the surface of the face paper sheet which contacts the relatively dense gypsum slurry is coated with the polymer;
• mixing water, calcium sulfate hemihydrate, and air to make a foamed gypsum slurry, wherein a weight ratio of the water to calcium sulfate hemihydrate being mixed is 0.2-1.5:1;
• depositing the foamed gypsum slurry directly on the first layer of relatively dense gypsum slurry to form a foamed gypsum core layer to locate the first layer of relatively dense gypsum layer between the gypsum core layer and the face paper sheet inner bond surface;
• wherein calcium sulfate hemihydrate in the foamed gypsum slurry and calcium sulfate hemihydrate in the relatively dense gypsum slurry convert to calcium sulfate dihydrate, and the foamed gypsum slurry and the relatively dense gypsum slurry set to form the gypsum board,
• wherein a foamed gypsum core layer resulting from the set foamed gypsum slurry has a thickness of 0.25 to 1 inches and a density of 15 to 55 pounds/cubic foot, wherein the foamed gypsum core layer resulting from the set foamed gypsum slurry has a total void volume of 30 to 90 volume percent;
• the relatively dense gypsum slurry having a density greater than that of the foamed gypsum slurry, the first layer of relatively dense gypsum slurry being thinner than the foamed gypsum core layer, wherein the set first layer of relatively dense gypsum resulting from setting the relatively dense gypsum slurry has a total void volume of less than 30 volume percent;
• wherein the polymer coating is at least partially not set at the time the first layer of relatively dense slurry is applied to the polymer coating;
• wherein the polymer coating contacts the face paper sheet and the set first layer of relatively dense gypsum;
• wherein at least a portion of the polymer coating penetrates from the inner bond surface of the face paper sheet through a portion of the face paper sheet, such that the latex polymer migrates through at least 20% of the face paper sheet thickness, but wherein the polymer coating does not uniformly penetrate into the first layer of relatively dense slurry, such that at least 90% of a thickness of the set first relatively dense gypsum layer has an absence of latex polymer;
• wherein the polymer coating applied has an absence of gypsum, wherein the polymer coating applied has an absence of calcium carbonate, wherein the polymer coating applied has an absence of magnesium carbonate, wherein the polymer coating applied has an absence of pigment, wherein the polymer coating applied has an absence of polyurea, and wherein the polymer coating applied has an absence of inorganic particles.