Small cracks in the bottom of rubber sole shoes appear naturally over time. The simple motion of walking is often enough to create small cracks. Other cracks can appear from the shoe ageing, or by repeatedly walking on rocky or rough surfaces that can crack the shoe's sole. Repairing small cracks is a very simple process. A tube of silicone caulk can hold the rubber sole together, while creating a waterproof barrier that prevents the shoes from taking in water. This repair can help extend the life of rubber soled-shoes by several months, or even years.
Wash the bottom of the soles with mild soap and a dish rag. Use a soft brush to scrape away any dirt or other objects from the bottom of the shoe, such as chewing gum. Dry the rubber sole with an old towel.
Inspect the bottom of the shoe for small cracks. Note where the cracks are located on the bottom of the shoe. Make sure you have enough caulk to fit between all of the cracks. It usually doesn't take much caulk, and one tube should be enough to repair both shoes.
Sand the bottom of the shoe lightly. Pay special attention to the cracks themselves. Pull apart the crack and sand each side of the crack, if possible. This helps roughen the surface of the rubber and helps it adhere to the caulk. Wipe the shoe with a damp rag to remove any rubber particles.
Work in a well-ventilated area. Apply a small line of silicone sealant between each crack in the shoe. Spread the silicone caulk inside the crack to create an even surface. Use the putty knife to apply a small amount of caulk outside the crack; feather it over both sides of the crack. Use a damp rag to wipe away any unwanted caulk from the bottom or sides of the shoes.
Place the shoe upside down on a flat surface. If the cracks do not hold together on their own, use a large clamp to hold the sole of the shoe in place. Wash your hands quickly to remove all traces of caulk from your fingers before it dries.