ARDEX E655 is a water dispersion primer and additive designed to improve shear and tensile bond of sand/cement screeds, plasters, render mortars and tile adhesives. It is used for treating porous substrates and materials. Thus, it can be used as a primer and additive to prevent gypsum substrates from breaking off from the chemical reaction between gypsum and cement aluminates; and to improve strength of cement/sand, mortar/screed.