To fix an exhaust with epoxy, wait until the exhaust has cooled before cleaning the area and applying the epoxy. Let it dry at least overnight, sand and then turn on the vehicle to heat up the exhaust, and check for further leaks.
Use a slightly damp rag when cleaning the area of the exhaust that needs repaired. Use a putty knife to apply the epoxy, and do so generously. Expand the application further than the area of repair. Extend it approximately 3 inches in each direction.
After the overnight waiting period, use sandpaper to smooth the area completely. Wipe any sandy epoxy residue away with a damp cloth before turning on the vehicle's engine. Allow it to heat up. The heat running through the exhaust bonds the epoxy to the surface. Once bonded, examine the exhaust to see if any other leaks occur.
Epoxy is made of mixture of resin and hardener. The hardener acts as a catalyst to cure the resin, and covalent bonds form between the resin and the hardener. This provides the rigid texture for which epoxy is known. By carefully choosing the resin and hardener combination, epoxy can be customized for application to a number of surfaces.