How to fix a hairline crack in a fiberglass tub

Written by jay kurz
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Cracks in showers or tubs can cause damage to the floor and surrounding areas. Instead of removing the old tub and buying a new one, you can repair the crack using a fibreglass filler. Fibreglass filler will seal the crack and retain a smooth surface. The repair will last for a long time and be unnoticeable if done correctly. Repairing a tub yourself will save a lot of money and time.

Skill level:

Things you need

  • Respirator
  • Coarse-grit sandpaper
  • Fine-grit sandpaper
  • Super fine-grit wet sandpaper
  • Fibreglass filler
  • Methyl ethyl ketone peroxide (hardener)
  • Putty knife
  • Rags
  • Acetone
  • Painter's tape
  • Gel coat gun
  • Gel coat
  • Boat wax

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  1. 1

    Sand the crack using coarse-grit sandpaper until all rough edges are smooth. Scuff all the way around the repair about 6 inches further than needed.

  2. 2

    Mix the fibreglass filler with the hardener as directed on the product labels. Using a putty knife, apply the filler to the crack. Smooth the filler until it is level with the surrounding fibreglass. Let the filler cure until it is hard and cool to the touch.

  3. 3

    Sand the filler and surrounding area smooth using a coarse-grit sandpaper followed by a fine-grit sandpaper.

  4. 4

    Clean the repair area using a rag and acetone. Thoroughly remove any grease or dust from the area.

  5. 5

    Tape off the perimeter of the repair and the surrounding surface using painter's tape.

  6. 6

    Mix the hardener with the gel coat as directed on the product containers and spray the first coat. The first coat should act as a base coat and be a heavy mist. Spray as consistently as possible for the best results. Let the first coat begin to get tacky and then apply the second and final coat. Let cure until hard and cool to the touch.

  7. 7

    Remove the tape and wet-sand the gel coat until it is smooth and blends in with the surrounding gel coat.

  8. 8

    Apply a couple coats of boat wax and buff until you achieve a shiny, finished surface. Use clean rags to buff the wax.

Tips and warnings

  • When working with fibreglass always wear a respirator.

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