Use CRL Bond Breaker Tape to create proper two-way sealant bonds. This clear, tough plastic tape with a clear polyethylene adhesive backing is eight mils (.2 mm) thick, and has high adhesion to steel or other structural metals. It is important for the sealant to bond to joints in two places so it can expand properly. If the sealant bonds in the wrong areas, it may tear or stretch to the point of failure. For sealing shallow joints Bond Breaker Tape is applied to the bottom of the joint so the sealant will bond only to the walls. For metal butt joints Bond Breaker Tape is applied to metal edges so the sealant can be "buttered" over the joint and can properly expand or contract.