GelCoat Trouble Shooting Guide
 

 

 

 

  1. Add Your Input

  2. Sagging and Runs

  3. Slow Gel/Cure

  4. Pinholes/Porosity

  5. Alligatoring

  6. Delamination

  7. Poor Hiding

  8. Poor Gloss

  9. Fiber Pattern

  10. Fish Eyes

  11. Dimples, Craters, Pock Marks

  12. Cracking and Crazing

  13. Prerelease

  14. Colour (Pigment) Separation

  15. Blisters

  16. Water Spotting

  17. Chalking

  18. Resin Tearing

  19. Poor Sprayability

Return to Main Menu

1.    Add Your Input

Rayplex welcomes your suggestions.  E-Mail comments, suggestions, or technical tips to info@fibreglass.com.

 

2.    Sagging and Runs

Problem:

As the gelcoat is being applied to the mould it slides or runs down the vertical surfaces.

Cause:

The viscosity and/or thixotropic index of the gelcoat itself is not high enough for the gelcoat to hold onto the vertical surface at the thickness that it is being sprayed at.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness, particularly in the problem area bullet

adjust spray equipment to ensure proper atomization bullet

check that the temperature of the gelcoat is between 18-25 deg.C bullet

avoid vibration or movement of the part after the gelcoat has been applied bullet

ensure gelcoat has been properly mixed bullet

review spray technique to minimize overspray bullet

ensure gelcoat has not separated with age, mix if required bullet

spray first up and down 5-7 mils, wait 2 minutes then spray side to side 5-7 mils.

3.    Slow Gel/Cure

Problem:

The gelcoat remains wet or is not ready to laminate in time to meet the standard production schedule.

Cause:

Insufficient catalyst, low temperatures, or other outside factors are affecting the normal cure rate of the gelcoat.  Insufficient air flow over curing gelcoat to remove styrene vapours.  High outside humidity.  Solvent with fast evaporation rate causing water vapour to condense. 

What to Do:

bullet

ensure gelcoat is being applied at the proper  thickness bullet

check catalyst output bullet

calibrate spray equipment bullet

ensure room temperature is above 18 deg.C bullet

ensure gelcoat temperatures are above 21 deg.C bullet

check shelf life of catalyst and gelcoat bullet

drain air lines and compressor tank to be sure air is free of moisture and other contaminants bullet

test sample gel cure in small cup.

4.    Pinholes/Porosity

Problem:

Upon demoulding, or after sanding the demoulded part, tiny holes are seen in the gelcoat surface.

Cause:

Bubbles of air or gas are trapped in the gelcoat when it gels.

What to Do:

bullet

adjust spray gun to improve atomization by lowering output volume of material. bullet

apply gelcoat in thinner passes - 6 mils wet max. bullet

use catalyst designed for reduced gassing bullet

lower pump pressures bullet

reduce catalyst levels bullet

try fast spray on first pass, increase output on 2nd & 3rd pass.

5.    Alligatoring

Problem:

Upon demoulding, areas of the gelcoat surface appear wrinkled and, in some cases, the back-up resin is visible.

Cause:

Laminate has been applied before the gelcoat is thoroughly cured or the resin gel time is too long, allowing the resin to partially dissolve the gelcoat.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness bullet

check catalyst output bullet

calibrate spray equipment bullet

ensure room temperature is above 18 deg.C bullet

ensure gelcoat temperatures are above 21 deg.C bullet

check tack-free time of gelcoat before laminating bullet

check shelf life of catalyst and examine for possible contamination bullet

drain air lines and compressor tank to be sure are is free of moisture and other contaminants bullet

if parting film is being used, ensure that it is dry before gelcoating bullet

use fingernail cure test; on back area of mould press hard on edge of thumb nail, if you cut through, gel still not cured.

6.    Delamination

Problem:

The cured gelcoat can easily be peeled away from the laminate.

Cause:

The laminating resin and the gelcoat did not form a proper bond during fabrication.  Air borne contaminants, PVA, oil, mist, wax, dust, etc. contaminate gel surface.

What to Do:

bullet

minimize the interval between the time the gelcoat is cured and the time it is laminated bullet

check for any sources of droplets of catalyst, solvent, dust or moisture that could end up on the gelcoat before lamination. bullet

mist coat the gelcoat surface with resin before applying fiberglass and resin bullet

use clean air to remove dust or contaminants from the gelcoat before laminating bullet

don't use cleaning or waxing rags to wipe dust off gelcoat bullet

do a bond sample, spray on test piece of thick plastic, if cured gel will crack.

7.    Poor Hiding

Problem:

The colour of the back-up laminate shows through the gelcoat making the surface colour uneven.

Cause:

The gelcoat is not opaque enough to completely block out the colour of the back up laminate.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness bullet

consider using a different colour with better hiding power bullet

colour the laminating resin.

8.    Poor Gloss

Problem:

Upon demoulding, the gelcoat surface is dull.

Cause:

The gelcoat is not well cured or the mould surface is poor.

What to Do:

bullet

using a wooden ruler, slightly tilted and placed on end, what # can be read in the mould? bullet

clean or resurface mould bullet

ensure gelcoat is being applied at the proper thickness bullet

check catalyst output bullet

calibrate spray equipment bullet

ensure room temperature is above 18 deg.C bullet

ensure gelcoat temperatures are above 21 deg.C bullet

check shelf life of catalyst and gelcoat bullet

drain air lines and compressor tank to be sure air is free of moisture and other contaminants bullet

if parting film is being used, ensue that it is dry before gelcoating.

9.    Fiber Pattern

Problem:

The outlines of glass fiber reinforcements, either chopped strand or woven roving, appear as distortions in the gelcoat surface.  May be seen when demoulding, shortly after demoulding, or when part is in service.

Cause:

While this generally is associated with resin problems or laminate construction, it is also caused by thin or under cured gelcoat.

What to Do:

bullet

see section on Alligatoring bullet

allow more time for the gelcoat to cure before laminating or speed up the cure of the gelcoat bullet

review laminate design and determine if skin coat is required bullet

switch to a higher heat distortion laminating resin bullet

allow more time before demoulding bullet

resin may cure too quickly causing high shrinkage.

10.    Fish Eyes

Problem:

Upon demoulding, transparent spots are seen in the gelcoat surface.

Cause:

The wet gelcoat fails to form a continuous surface because the gelcoat viscosity is too low or the mould surface is contaminated.

What to Do:

bullet

check for possible sources of oil or water droplets and eliminate source bullet

check air lines for contamination bullet

ensure mould surfaces are clean before gelcoating bullet

adjust spray gun to ensure proper atomization bullet

check shelf life of gelcoat bullet

ensure gelcoat has been properly mixed bullet

ensure gelcoat is being applied at the proper thickness bullet

oil mist for oil lubricators on material pump, or chopper gun motors, might be contaminating the air and in turn settling on the mould.  Check exhaust mist mufflers. 

Return to Main Menu

11.    Dimples, Craters, Pock Marks

Problem:

Shortly after demoulding, small concave indentations appear in the surface of the gelcoat.

Cause:

Can result from contamination of the gelcoat, but is generally caused by imperfections, such as trapped air, in the laminate.  Gelcoat drops that are either over or under-catalyzed on mould surface.  Spray tips dirty.

What to Do:

bullet

check for possible sources of contamination bullet

check spray fan for good catalyst mixing bullet

check shelf life of gelcoat bullet

improve workmanship in lamination to ensure air is removed bullet

ensure gelcoat is being applied at proper thickness bullet

check tack free time of gelcoat before laminating bullet

allow more time before demoulding bullet

check spray gun nozzel for possible dripping gelcoat.

12.    Cracking and Crazing

Problem:

A partial fracture (cracking) or straining (crazing) of the gelcoat surface occurs during demoulding or while the part is in service.

Cause:

Gelcoat is applied too thick in high stress areas of a part or parts are demoulded when they are too green.  In service, these result from high stresses such as flexing, impact, or vibration in the laminate.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness, particularly in high stress areas bullet

ensure that parts are sufficiently well cured before demoulding bullet

check that proper catalyst levels are being used and that catalyst is being well mixed bullet

for cracking in service, review design of laminate for proper thickness and reinforcement content bullet

for cracking in service, switch to a more resilient gelcoat product bullet

review overall product design bullet

observe safety practices using air assisted releases.

13.    Prerelease

Problem:

Upon demoulding, a subtle surface distortion is seen that usually runs along a distinct line where on one side of the line the gelcoat appears normal and on the other side it is dull.

Cause:

Gelcoat pulls away from the mould surface in some areas before it is properly cured due to uneven thickness or catalyzation.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness, particularly in corners bullet

lower catalyst level and ensure that catalyst is being properly mixed bullet

minimize the interval between the time the gelcoat is cured and the time it is laminated bullet

review mould preparation bullet

check for mould contamination.

14.    Colour (Pigment) Separation

Problem:

Upon demoulding, the gelcoat surface has small coloured specks or fine coloured streaks in certain sections, commonly where there are tight radii or deep draws.

Cause:

Most custom gelcoat colours contain pigments of different particle size.  When shear is applied to the gelcoat, these pigments can separate from each other, making the colour uneven.

What to Do:

bullet

ensure gelcoat has been properly mixed bullet

check shelf life of gelcoat bullet

drain air lines and compressor tank to be sure air is free of moisture and other contaminants bullet

lower pump pressures bullet

ensure spray gun is held at right angles to the mould at all times bullet

minimize overspray bullet

do not allow gelcoat to flood or flow along mould surface when spraying bullet

spray gelcoat in thin passes - right to left then up and down.

15.    Blisters

Problem:

Shortly after demoulding, or after the part has been in service for some time, small bubbles appear in the gelcoat surface.

Cause:

Contamination or air bubbles between gelcoat and the laminate cause poor adhesion.  Heating of the laminate or extended water exposure can result in swelling in these areas.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness bullet

improve workmanship in lamination to ensure air is removed bullet

check for any sources of droplets of catalyst, solvent, or moisture that could end up on the gelcoat before lamination bullet

mist coat the gelcoat surface with resin before applying fibreglass and resin bullet

ensure spray equipment is in proper working order bullet

review selection of gelcoat and resin types if blisters are occurring in marine applications (refer to osmotic blistering).

Return to Main Menu

16.    Water Spotting

Problem:

Gelcoat surface whitens where kept in direct contact with water or moisture.

Cause:

Exposure to water or moisture will quickly cause whitening if the gelcoat is not well cured.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness bullet

check catalyst output bullet

calibrate spray equipment bullet

ensure room temperature is above 18 deg.C bullet

ensure gelcoat temperatures are above 21 deg.C bullet

check shelf life of catalyst and gelcoat bullet

drain air lines and compressor tank to be sure air is free of moisture and other contaminants bullet

review gelcoat type with supplier where dark colours are being used.

17.    Chalking

Problem:

Rapid loss of gloss on gelcoat surface upon outdoor exposure.

Cause:

The combination of UV radiation and moisture act to degrade the polyester, exposing the fillers and pigments in the gelcoat.  This can happen quickly if gelcoat is not well cured.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness bullet

check catalyst output bullet

calibrate spray equipment bullet

ensure room temperature is above 18 deg.C bullet

ensure gelcoat temperatures are above 21 deg.C bullet

check shelf life of catalyst and gelcoat bullet

drain air lines and compressor tank to be sure air is free of moisture and other contaminants bullet

review gelcoat type with supplier bullet

make test sample sprayed @ different catalyst levels.

18.    Resin Tearing

Problem:

Upon demoulding, clusters of short, fine, dark lines are found in the gelcoat surface.

Cause:

Under shear, the fillers and pigments can separate leaving clear resin in the voids.

What to Do:

bullet

ensure gelcoat is being applied at the proper thickness, particularly in problem area bullet

ensure gelcoat has been properly mixed bullet

check shelf life of gelcoat bullet

drain air lines and compressor tank to be sure air is free of contaminants bullet

lower pump pressures bullet

ensure spray gun is held at right angles to the mould at all times bullet

do not allow gelcoat to flood or flow along mould surface when spraying bullet

check mould after spraying for hot or cold spot sources.  Vibrations can cause separation.

 

19.    Poor Sprayability

Problem:

Gelcoat is thicker than normal and spray gun will not deliver the product despite being set to normal operating settings and pressures.

Cause:

Low temperature or contamination, such as gelled material or water, affects the viscosity of the gelcoat.  Old  material.

What to Do:

bullet

warm the gelcoat to above 21 deg.C bullet

check shelf life of gelcoat bullet

check for contamination due to improper storage bullet

drain air lines and compressor tank to be sure air is free of moisture bullet

clean the filter in the spraying equipment bullet

ensure equipment is in good working order bullet

check spray gun for restricted fluid line passage bullet

visually judge viscosity against known good material. bullet

 

Email us with your comments
Rayplex Limited  341 Durham Crt.  Oshawa, Ont  Canada  L1J 1W8
 PH (905)  579-1433    FX (905)  579-1431
We are open for business Monday to Friday - 9 am. to 5pm.  E.S.T.    
 
View Rayplex's Operational TERMS & CONDITONS of doing Business
Copyright 2017 Rayplex Limited     RAYPLEX  is a registered Trade Mark  All rights reserved.