How to repair cracked resin sink basins

Updated February 21, 2017

Sinks that are constructed out of fibreglass resin are very durable and long lasting. Fibreglass is a lightweight material that consists of layers of reinforced fibreglass mat or cloth that are saturated in catalysed resin. Even though fibreglass is a strong material, on pieces like a sink when the fibreglass is very thin it can be brittle in some areas. Commonly sinks will develop small fractures or cracks in weak spots of the sink and will need to be repaired or replaced to avoid water leakage. Repairing a small crack yourself is much cheaper and faster than replacing the sink all together. Fibreglass sink repair materials can be found at your local home improvement store.

Put on a respirator and lightly grind a grove directly on the crack until all the damage fibreglass is smooth using a dye grinder. Gradually taper the edges of the grove to give the fibreglass filler a maximum amount of surface area to bond to.

Clean the surface of the repair area using a rag damp with acetone to remove any contaminants such as grease or oil residue.

Put on a pair of rubber gloves and catalyse a small amount of fibreglass filler using one to two per cent catalyst. Use your hands to mead the catalysed filler until it is one consistent colour the catalyst is completely mixed in.

Fill the grove with the filler and smooth it out with a putty knife. Make the filler as smooth as you want the final surface to be so you don't have too much sanding to do. Let the filler harden for at least an hour or until it's hard and cool to the touch.

Sand the filler completely smooth and level with the surrounding fibreglass using 100-grit sandpaper. Clean the repair with a rag and acetone.

Mix a small amount of gel coat with one to two per cent catalyst and mix it together using a stir stick. Lightly apply the gel coat with a soft bristle paint brush until the repair is smoothly covered. Let the gel coat harden.


Always wear a respirator when working with fibreglass materials.

Things You'll Need

  • Safety glasses
  • Respirator
  • Dye grinder
  • Rubber gloves
  • Small bucket
  • Fibreglass filler
  • Catalyst
  • Putty knife
  • 100-grit sandpaper
  • Gel coat
  • Paint brush
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About the Author

Jason Kurz has been a published writer for and for less than a year now. Kurz attended Kent State University of Ohio for Computer Aided Design.