The disclosure provides a coating composition for improving the sag resistance of a fibrous panel, the composition including 10 to 100 wt. % inorganic binder, based on the total weight of the dry coating, wherein the inorganic binder includes a borate salt and at least one of an alkali metal silicate or an alkaline earth metal silicate, and the inorganic binder is water soluble. Further provided are fibrous panels having a backing side and an opposing facing side including the coating of the disclosure, and methods of preparing same.