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Gelcoat Troubleshooting Guide

DescriptionPossible CausesSolution
DelaminationGel Coat ContaminationCheck lines and drain traps for wax/contaminants and dust on the mold.
Gel Coat Over Cured Laminate gel coat the same day.
Color SeparationImproper Spray TechniqueSpray perpendicular to the mold.
Pump Pressure Too HighReduce air pressure.
Sagging or RunningApply 18- 22 mils of gel coat.
Resin TearingPump Pressure Too HighReduce for proper fan pattern with no tails.
Improper Spray TechniqueUse proper technique to spray mold. Check for water contamination.
FisheyesMold ContaminationFreshly waxed mold, flange wax on mold surface. Empty line traps of water and oil and review your waxing schedule.
Low-viscosity Gel CoatMix gel coat 10 minutes maximum per day. Old material-rotate your stock.
Pinholes/CratersImproper Pump PressureIncrease or decrease pump pressure for proper atomization.
Catalyst on MoldCheck for equipment malfunction.
Contaminants on MoldDrain traps, review wax schedule.
Low-viscosityReplace aged material.
EquipmentClogged gun, clean.
Sagging/RunningLow-viscosity Gel CoatMix gel coats 10 minutes maximum per day.
Gel Time Too LongIncrease catalyst and talk to vendor.
Mold Release WaxCheck for silicone.
Fiber PatternThin Gel CoatEnsure you have 18 - 22 mils applied.
Poor Mold SurfaceReview and refinish mold if needed.
Gel Coat Not CuredEnsure proper cure before laminating.
Laminate Exotherm Too HotReduce catalyst and talk to vendor.
Post-cure of the LaminateEnsure proper cure before pulling part.
DescriptionPossible CausesSolution
Dull Parts During PullingPolystyrene or Wax BuildupStrip the molds and rewax.
Poor Mold GlossBuff out the molds and rewax.
Parts Pulled Too SoonEnsure a proper cure before pulling part.
Dull Parts After PullingParts Experiencing Post-cureEnsure proper cure before pulling part.
Pre-releaseThin and Thick Areas of Gel CoatUse proper spray technique with 18 - 22 mils.
Hot and Cold Spots on the MoldProvide a maximum mold temperature of 85 - 90°F.
Catalyst Too High for Shop ConditionsReduce catalyst to no less than 1.25%.
Parts Sat OvernightLaminate parts within several hours after gel coating.
PorosityGel Coat Too ThickApply three uniform coats 18 - 22 mils.
Pump Pressure Too HighReduce pressure for proper pattern with no tails.
Low HAP Gel CoatUse an in-line heater.
Gun Too Close to MoldApply gel coat 16 - 30 inches from mold.
Gel Coat Too ColdApply gel coat at 70 - 80°F
AlligatoringGel Coat Too ThinApply gel coat 18 - 22 mils.
Improper Catalyst AtomizationCheck catalyst pot or slave.
Wrong Gel Time for PartEnsure proper working time, do not apply gel coat on a partially cured part.
Gel Coat Not CuredLaminate the gel coat when the gel coat is dry to the touch.
BlistersLaminate Not Rolled Out ProperlyRoll all the air out of the laminate.
Catalyst DropsEnsure proper atomization and gun maintenance.
Spider CracksImpact from Laminate Side of PartCheck handling and demolding process.
Stress CracksExcess Gel Coat ThicknessUse a mil gauge.
Parts Pulling Too HardIncrease the frequency of mold release application.


Physical separation of the gel coat film from the laminate.
Pinholes go through the gel coat surface. Craters can only be seen on the back side of the gel coat.
Air trapped within the gel coat film. This can be seen as micro air or can be seen as small pits.
Color Separation:
Streaks or color variation seen on the gel coat surface.
Sagging is a horizontal buildup of gel coat, and a run is a vertical buildup of gel coat.
The surface of the gel coat appears wrinkled. This can appear before or after lamination.
Resin Tearing:
Physical separation of the pigments from the resin. Can be seen as gray streaks.
Fiber Pattern/Print:
Transfer of the laminate pattern or texture to the finished gel coat surface.
Small air voids which can be seen between the gel coat and the laminate.
Incomplete coverage of the substrate.
Physical listing of the gel coat film from the mold. This can occur before lamination and after lamination.

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