The AL-HARD rigidizer/hardener is used to increase the hardness of Zircar refractory sheet products. It consists of aluminum oxide and phosphoric acid in a water base. Refractory sheet products treated with AL-HARD are ready to use after drying. When a chemical bond forms, it hardens the fibrous material. The degree of hardening depends on the amount of AL-HARD used. It is nonflammable and is not affected by freezing. It can be applied by immersing, spraying, brushing or sponging on many of the refractory sheet products.