15 J-B Weld is a remarkable two-part epoxy resin, cold-weld compound designed to bond or fill. Use it on pitted iron or aluminum surfaces, then work smooth once it cures. J-B Weld has even been successfully used on cracked blocks and heads by following instructions to the letter. Use J-B Weld to salvage damaged castings. It is waterproof, heat resistant (up to 500-degrees F), chemical tolerant, workable for 30 minutes, and will cure fully in 15-24 hours.