How to repair spiderweb cracks in fiberglass with gelcoat

Written by kimberly johnson
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How to repair spiderweb cracks in fiberglass with gelcoat
Small cracks in fibreglass are called crazing. (NA/ Images)

Gelcoat is an upper layer that is applied to fibreglass objects that colours the fibreglass and creates a shiny finish. Gelcoat is typically durable but will crack if excessive pressure is applied to it. Shallow cracks sometimes resemble spiderwebs and are called "crazing." These cracks are superficial, and repair is only required to improve the appearance of the object. By removing the upper gelcoat layer and applying a fresh layer, the cracks will disappear.

Skill level:
Moderately Easy

Things you need

  • Electric grinder
  • Medium-grit sandpaper
  • Safety glasses
  • Dust mask
  • Rags
  • Gelcoat
  • Paintbrush
  • Fine-grit sandpaper
  • Polishing compound
  • Orbital buffer (optional)

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  1. 1

    Attach medium-grit sandpaper to an electric grinder and plug the cord of the grinder into an electrical socket. Put on safety glasses and a dust mask.

  2. 2

    Turn on the grinder, and sand down the portions of the gelcoat that have the spiderweb cracks in them. Sand all the way down to the fibreglass underneath the gelcoat. The fibreglass itself feels like stiff fabric.

  3. 3

    Wipe down the area with a damp rag to remove any sanding dust. Paint the area with fresh gelcoat by either hand-painting with a brush or by spraying it on, depending on which method you are most comfortable with. If you use a brush, do not worry about the brush strokes, since they will be sanded off later.

  4. 4

    Wait until the gelcoat hardens completely according to the drying time specified on the bottle. Resand the area with a fine-grit sandpaper, just until the surface of the new gelcoat is flush with the surrounding surface. Run your hand over the repaired area to determine when it is smooth.

  5. 5

    Apply 1 to 2 tsp of polishing compound to a rag and apply it to the repaired area. Polish the gelcoat by moving the rag in a circular motion until the repaired area is shiny. If you are repairing a large area, you can use an orbital buffer tool to speed the process.

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