1 lb. of boric acid (U.S.P.) was dissolved in 11 lbs. of 28 wt. percent aqua ammonia. 50 lbs. of water are added and then 2.2 lbs. of polyvinyl acetate homopolymer aqueous dispersion (emulsion) containing 55 wt. percent solids (du Pont Elvacet). 3 lbs. finely ground ZnSO -7H O are then dissolved in the solution and it is made up with water to a total weight of 100 lbs. Then 170 lbs. of finely ground steam calcined plaster of Paris are thoroughly stirred into the solution and the slurry is coated upon gauze as in Example 1. The slurry coated gauze was dried at 240 F. as before. The final, dry product showed a setting-time of 3% minutes by the method of Example 1 and otherwise met the Federal Specification cited.