Fiberglass sinks are durable but can become cracked or fractured over time. Fiberglass is easy to work with and often can be repaired to original strength no matter what the failure is. Fiberglass filler commonly is used to fill small cracks in fiberglass. Filler is basically fiberglass resin that has additives which turn the resin into a thick consistency. Filler requires a catalyst to harden and is applied with a putty knife. All the supplies needed to fix a fiberglass sink can be found at your local marine supply store.
Things You'll Need
Coarse grit sandpaper
Methyl ethyl ketone peroxide (hardener)
Fine grit sandpaper
Fiberglass gel coat
Sand the crack using coarse grit sandpaper until it is no longer visible. Don't go through the fiberglass but remove the entire crack until the fiberglass is smooth. This might form a groove were the crack was. Gradually taper the edges of the groove to give the filler more surface area to bond to.
Clean the surface of the repair using a rag and acetone. Remove any dust or grease that may be on the surface.
Mix the filler and hardener as directed on the containers. Use a small bucket and stir stick to thoroughly mix the filler. When the filler is one consistent color apply it to the repair. Use a putty knife and smooth the filler out. Let the filler cure until it is hard and cool to the touch.
Sand the filler smooth using fine grit sandpaper. Scuff an extra 2 to 3 inches around the repair.
Mask off the sink up to the edge of the scuffed area. The gel coat will only bond to scuffed surfaces.
Mix the gel coat and hardener as directed on the containers using a small bucket and a stir stick. When the gel coat is thoroughly mixed, apply it to the repair using a paint brush. Let the gel coat harden for at least 24 hours before running the water.