Thule boxes are mounted to the roofs of vehicles and used for storage. The units sometimes take a beating because they are exposed to the elements, stray rocks and debris. If your Thule box has seen better days, it can be repaired with items easily found at most hardware or home-improvement stores. Repairing a cracked Thule box is a project most people can achieve in one afternoon or less.
Sand the area around the crack inside the Thule box. Use only coarse-grit sandpaper, instead of fine-grit, so fiberglass will adhere better.
Cut at least two sections of fiberglass cloth. Each section should be at least two inches beyond the edge of the crack in all directions.
Mix the epoxy using the ratios specified on the package. Put mixed epoxy on a disposable paper plate.
Apply a layer of epoxy to the sanded area on the Thule box.
Place the fiberglass fabric over the crack. Remove air bubbles from the applied fiberglass with a squeegee.
Repeat this process with epoxy and your second layer of fiberglass. If you choose to use more than two layers, continue to repeat this process until all layers are used.
Apply another thin layer on top of your final piece of fiberglass. Squeegee any air bubbles out to seal the fiberglass matting.
