An under counter mount sink sealing surface and method of making that provides a watertight interface between an under counter mount sink and a laminate counter as well as a simplified and more dimensionally accurate method of field installing the sink below the counter. The water impervious seal is tightly chemically bonded to the cutout lip of the laminate as well as to the entire area on the bottom face of the laminate countertop that contacts the entire profile of the top face of the under counter mount sink. The seal also aligns the sink into the correct location and contacts the entire surface of the as it is deck aligned or completely parallel to the sink top flange.