Identification

• Inspect the fiberglass pool thoroughly to determine the location of the crack or leak. If it is not visible, add drops of food coloring into the water and watch the color flow toward the crack and then out. If it appears the color is not moving, give it some time. Drain the pool so the water level lies below the crack.
  
  

Preparation

• Sand the surface around the crack to remove debris. Extend the length and depth of the crack slightly using a saw with a diamond blade. Add fiberglass repair filler to a bucket along with the required amount of catalyst according to the manufacturer's directions. Mix them together to a workable consistency.
  
  

Procedure

• Scoop some prepared filler from the bucket and insert it into the crack with a putty knife. Rub the repaired section with a 200-grit sandpaper, paying special attention to the edges, so they blend with the surrounding fiberglass surface.
  
  

Finishing Touches

• Spread fiberglass cloth strips over the repaired area and coat with an even layer of gel coat. Roll the gel with a roller to remove trapped air and leave it to dry thoroughly.