Sag in ceiling tiles is reduced by the present coated ceiling tile and method which decreases sag in the coated ceiling tiles. Calcined gypsum and water are combined to form a coating which is applied to the back side of a base ceiling tile in a thin layer of about 100 micrometer to about 1000 micrometers. The coating optionally includes a set time modifier. This method makes a coated ceiling tile from a base ceiling tile having a front side and a back side opposing the front side. The coating is applied to the back side of the base ceiling tile, the coating comprising an interlocking matrix of calcium sulfate dihydrate. Optionally, remnants of the set time modifier are present within interstices in the gypsum matrix. The remnants of the set time molecule include ions, molecules, particles or combinations thereof.