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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:
ensure gelcoat is being applied at the proper thickness, particularly in the problem area
adjust spray equipment to ensure proper atomization
check that the temperature of the gelcoat is between 18-25 deg.C
avoid vibration or movement of the part after the gelcoat has been applied
ensure gelcoat has been properly mixed
review spray technique to minimize overspray
ensure gelcoat has not separated with age, mix if required
spray first up and down 5-7 mils, wait 2 minutes then spray side to side 5-7 mils.
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:
ensure gelcoat is being applied at the proper thickness
check catalyst output
calibrate spray equipment
ensure room temperature is above 18 deg.C
ensure gelcoat temperatures are above 21 deg.C
check shelf life of catalyst and gelcoat
drain air lines and compressor tank to be sure air is free of moisture and other contaminants
test sample gel cure in small cup.
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:
adjust spray gun to improve atomization by lowering output volume of material.
apply gelcoat in thinner passes - 6 mils wet max.
use catalyst designed for reduced gassing
lower pump pressures
reduce catalyst levels
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:
ensure gelcoat is being applied at the proper thickness
check catalyst output
calibrate spray equipment
ensure room temperature is above 18 deg.C
ensure gelcoat temperatures are above 21 deg.C
check tack-free time of gelcoat before laminating
check shelf life of catalyst and examine for possible contamination
drain air lines and compressor tank to be sure are is free of moisture and other contaminants
if parting film is being used, ensure that it is dry before gelcoating
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:
minimize the interval between the time the gelcoat is cured and the time it is laminated
check for any sources of droplets of catalyst, solvent, dust or moisture that could end up on the gelcoat before lamination.
mist coat the gelcoat surface with resin before applying fiberglass and resin
use clean air to remove dust or contaminants from the gelcoat before laminating
don't use cleaning or waxing rags to wipe dust off gelcoat
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:
ensure gelcoat is being applied at the proper thickness
consider using a different colour with better hiding power
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:
using a wooden ruler, slightly tilted and placed on end, what # can be read in the mould?
clean or resurface mould
ensure gelcoat is being applied at the proper thickness
check catalyst output
calibrate spray equipment
ensure room temperature is above 18 deg.C
ensure gelcoat temperatures are above 21 deg.C
check shelf life of catalyst and gelcoat
drain air lines and compressor tank to be sure air is free of moisture and other contaminants
if parting film is being used, ensue that it is dry before gelcoating.
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:
see section on Alligatoring
allow more time for the gelcoat to cure before laminating or speed up the cure of the gelcoat
review laminate design and determine if skin coat is required
switch to a higher heat distortion laminating resin
allow more time before demoulding
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:
check for possible sources of oil or water droplets and eliminate source
check air lines for contamination
ensure mould surfaces are clean before gelcoating
adjust spray gun to ensure proper atomization
check shelf life of gelcoat
ensure gelcoat has been properly mixed
ensure gelcoat is being applied at the proper thickness
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.
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:
check for possible sources of contamination
check spray fan for good catalyst mixing
check shelf life of gelcoat
improve workmanship in lamination to ensure air is removed
ensure gelcoat is being applied at proper thickness
check tack free time of gelcoat before laminating
allow more time before demoulding
check spray gun nozzel for possible dripping gelcoat.
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:
ensure gelcoat is being applied at the proper thickness, particularly in high stress areas
ensure that parts are sufficiently well cured before demoulding
check that proper catalyst levels are being used and that catalyst is being well mixed
for cracking in service, review design of laminate for proper thickness and reinforcement content
for cracking in service, switch to a more resilient gelcoat product
review overall product design
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:
ensure gelcoat is being applied at the proper thickness, particularly in corners
lower catalyst level and ensure that catalyst is being properly mixed
minimize the interval between the time the gelcoat is cured and the time it is laminated
review mould preparation
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:
ensure gelcoat has been properly mixed
check shelf life of gelcoat
drain air lines and compressor tank to be sure air is free of moisture and other contaminants
lower pump pressures
ensure spray gun is held at right angles to the mould at all times
minimize overspray
do not allow gelcoat to flood or flow along mould surface when spraying
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:
ensure gelcoat is being applied at the proper thickness
improve workmanship in lamination to ensure air is removed
check for any sources of droplets of catalyst, solvent, or moisture that could end up on the gelcoat before lamination
mist coat the gelcoat surface with resin before applying fibreglass and resin
ensure spray equipment is in proper working order
review selection of gelcoat and resin types if blisters are occurring in marine applications (refer to osmotic blistering).
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:
ensure gelcoat is being applied at the proper thickness
check catalyst output
calibrate spray equipment
ensure room temperature is above 18 deg.C
ensure gelcoat temperatures are above 21 deg.C
check shelf life of catalyst and gelcoat
drain air lines and compressor tank to be sure air is free of moisture and other contaminants
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:
ensure gelcoat is being applied at the proper thickness
check catalyst output
calibrate spray equipment
ensure room temperature is above 18 deg.C
ensure gelcoat temperatures are above 21 deg.C
check shelf life of catalyst and gelcoat
drain air lines and compressor tank to be sure air is free of moisture and other contaminants
review gelcoat type with supplier
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:
ensure gelcoat is being applied at the proper thickness, particularly in problem area
ensure gelcoat has been properly mixed
check shelf life of gelcoat
drain air lines and compressor tank to be sure air is free of contaminants
lower pump pressures
ensure spray gun is held at right angles to the mould at all times
do not allow gelcoat to flood or flow along mould surface when spraying
check mould after spraying for hot or cold spot sources. Vibrations can cause separation.
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:
warm the gelcoat to above 21 deg.C
check shelf life of gelcoat
check for contamination due to improper storage
drain air lines and compressor tank to be sure air is free of moisture
clean the filter in the spraying equipment
ensure equipment is in good working order
check spray gun for restricted fluid line passage
visually judge viscosity against known good material.