Xtra Bond Additive is a resin additive that prepares the surface to be bonded which increases the adhesive bond of the resin to the glass. To use, add 1 drop additive to 4-5 drops of resin into your injector and mix with a toothpick. Then complete the repair. One bottle will do 60 stone-breaks. Recommended for Star and Combination breaks in the defroster area.