Exploring Common Gelcoat Faults

Gelcoats provide a durable and reliable finish when handled appropriately, but faults may occur for several reasons. This article summarizes some common causes of gelcoat faults and their reasons.

Exploring Common Gelcoat Faults

Image Credit: Scott Bader Company Ltd.

Color tearing:

  • Long geltime or sagging
  • The use of improper spray techniques
  • Pigment becoming separated from resin

Color separation:

  • Poor application of the gelcoat
  • Drainage or sagging
  • Insufficient mixing

Color mottling:

  • The gelcoat being low in thixotropy
  • Low viscosity
  • Poor pigment compatibility

Parallel cracks:

  • The laminate being too thin or flexible
  • A thick gelcoat
  • Flex cracking

Star cracking:

  • The transfer of crack pattern from mold to surface
  • The gelcoat being too thick
  • Reverse impact

Crazing:

  • Contamination
  • Chemical attack
  • Excess heat

Blisters on laminates:

  • The presence of air voids
  • Water ingress
  • Damp reinforcement

Gelcoat blisters:

  • Solvent contamination
  • Unreacted catalyst
  • Air voids on release

A fiber pattern:

  • The gelcoat being too thin
  • High exotherm in the laminate
  • Insufficient cure, or the cure being released too soon

Exploring Common Gelcoat Faults

Image Credit: Scott Bader Company Ltd.

Color specks:

  • Pigments being mixed or ground poorly
  • Contamination
  • Equipment being improperly maintained

Sagging:

  • The gelcoat being too thick
  • The geltime being too long
  • Low viscosity or thixotropy

De-wetting (brush):

  • The brush gelcoat being applied too thinly
  • Use of an incompatible release system
  • Contamination

De-wetting (spray):

  • The spray gelcoat being applied too thinly
  • Use of an incompatible release system
  • Contamination

Wrinkling:

  • The gelcoat being too thin
  • The backup being too early
  • Insufficient cure

Gelcoat peeling:

  • The gelcoat being too fully cured
  • Contamination
  • The geltime being too long, resulting in the wax being dissolved

Watermarking or etching:

  • Solvent attack
  • Two colors being gelcoated on the mold
  • Areas of thin, double gelcoating on the mold

Dimpling:

  • Contamination
  • Insufficient consolidation
  • Too heavy wet-on-wet spray application

Porosity:

  • The gelcoat being too viscous to adequately release air
  • Gelling occurring too quickly, trapping air
  • A cold gelcoat and/or mold
  • The application of spray gelcoat with too high pressure or too low catalyst levels

Proper gelcoat application is key to minimizing these risks.

Acknowledgments

Produced from materials originally authored by Scott Bader Company.

This information has been sourced, reviewed and adapted from materials provided by Scott Bader Company Ltd.

For more information on this source, please visit Scott Bader Company Ltd.

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