This is the slow-speed option of the three available catalyst speeds (fast, medium, slow) for use with House of Kolor UC21 Universal Acrylic Urethane Klear. It’s a hardener for UC21 clear, mixed at a 2:1 ratio (clear to catalyst), and is best suited for hot weather or larger jobs requiring extra working time. House of Kolor catalyst is for use with House of Kolor paints only — due to their unique chemistry, House of Kolor Catalyst should never be substituted with other brands of catalysts.