Description J-B Weld pro-size is the original cold-weld two-part epoxy system that provides strong, lasting repairs to metal and multiple surfaces. Mixed at a ratio of 1:1, it forms a permanent bond and can be shaped, tapped, filed, sanded and drilled after curing. At room temperatures, J-B Weld sets in 4-6 hours to a dark grey color. A full cure is reached in 15-24 hours. J-B Weld has a tensile strength of 5020 psi and sets to a hard bond overnight. It can withstand temperatures up to 550ÂF when fully cured.