Coatings for building products and dewatering aid for use with same

A dewatering aid for dewatering a cementitious slurry coating on a product, said dewatering aid comprising a particulate material in an effective quantity and particle size to maintain porosity in the slurry and the product to be coated during dewatering and thereby permit dewatering of the slurry through the product to be coated, wherein said dewatering aid comprises about 25-60 wt % silica, about 10-30 wt % Al2O3, about 5-25 wt % Fe2O3, about 0-20 wt % CaO, about 0-5 wt % MgO, wherein a first portion of the particulate material has a larger particle size of about a 100 micron maximum size in the amount of about 10 to 60 wt % of the cementitious slurry based on total dry ingredients and a second portion of the particulate material that is a smaller particle size of about a 10 micron maximum size in the amount of 5 to 30 wt. % of the formulation based on total dry ingredients, and wherein the slurry is up to 50% water, wherein the water is based on percent by total weight of solids.