1. INTRODUCTION—Even under the best of conditions, problems can occur due to accidents, mistakes and unanticipated changes. Listed are some of the various problems that can occur and how to solve them. Also remember that the gel coat is affected by the laminate, and good gel coat will not compensate for a poor laminate.
2. PROBLEM DIAGNOSIS—To isolate and diagnose the problem, give consideration to the following :
A. What does the defect look like?
B. Where does it occur? All over, random, isolated side or section?
C. Is it on all parts, some of the parts, or just one?
D. When did it first occur? Or when was it first observed?
E. Does it match up to a defect in the mold?
F. When were the defective parts sprayed?
1) Did it occur during a particular shift? Or from a particular spray operator?
2) Was it during a particular part of the day— when it was hot, cold, damp, or other?
G. Did the problem occur through all spray stations or just one in particular?
H. Where does it occur? In the gel coat film? Against
the mold? On the back side? Within the film?
I. What is the code, batch number, and date of the gel coat with which the problem is occurring? Were
good parts sprayed from this batch or drum?
J. Was anything done differently, such as a change in catalyst level, spray operator, method of application, or weather conditions?
K. How would someone else identify or describe the defect?
L. What were the weather conditions at the time the
part was sprayed?
M. What corrective steps were taken and were they effective?
N. Check the material or laminate that was applied to or on the gel coat.
Listed on the following pages are common gel coat problems and their usual solutions.
Photographs illustrating many of these problems are also included.
Common Gel Coat Problems and Solutions
| PROBLEM
| CAUSE
| SOLUTION OR ITEMS TO CHECK FOR  | |
| Material gelled—in container ………………. | Age ………………………….. Storage condition ………. | Use partial container first; keep covered. Use within storage limitations. | |
| Jagged tape lines ….. | Gel coat starting to gel … | Use less catalyst (do not go below recommended minimum). Use double tape process. Use good tape recommended for fine lines. | |
Pigment darting or specks ………………….. | Contamination ……………. Foreign particles ……….. | Clean pump and lines. Strain and keep material covered. Keep overspray minimized; be sure molds are clean; spray perpendicular to mold surface. | |
| Pigment separation or mottling …………………
| Pigments separate from each other ……………….. Other ………………………….. | Check for contaminants such as water or solvent. Dirty equipment. Dry over-spray. (Keep a wet line.) Excessively applied gel coat causing sagging. Excessively high delivery rates causing flooding onto the mold surface. | |
| Pinholes ……………….
| Insufficient atomization …. | Too high gel coat delivery rate. Not enough atomizing pressure. | |
| Porosity ………….
| Entrapped air ……………… Wrong catalyst………………. No catalyst ……………………. Gel coat film thickness ……. Formulation …………………… Water or solvent ……………. | Wrong air pressure. Too high tens to yield fine porosity; too low will produce larger, surface porosity.Check gel coat vendor for recommendation. Check catalyst supply and alignment. Applied too thick; use 18 ± 2 mils wet. Apply in two to Improper viscosity and/or resin solids. Check with vendor. Check for contamination. Check pump for air leaks. Mix once a day for 10 minutes only. | |
| Pre-release of the gel coat— During cure, causing obvious surface distortion and low gloss ……………………
Occurring after cure; observed as visible | Wrong catalyst …………….. High catalyst level …………. Low catalyst level ………….. Uneven and/or too thick Gel coat allowed to cure Gel coat resin solids too low ………………………. Uneven cure …………….. Mold release ……………. Clay ………………………… Too long of cure ………… Laminate curing too fast …… Wrong type resin ….. | Refer to CCP recommended catalyst list. Calibrate equipment and decrease catalyst. Calibrate equipment and increase catalyst. Check thickness, not to exceed, not to exceed 24 mils, wet. Ensure a consistent film thickness. Gel coat should not be allowed to set on the mold for more than a few hours without laminating at least a skin coat. Varies with temperature—should be laminated same day. Check with manufacturer; do not add styrene without Improperly dispersed catalyst. Laminate sooner—don’t lap or jar the mold. Check for proper catalyst level. Build laminate in stages. Too high in exotherm. | |
| Resin tearing—or resin separation …………
| Pigments separate from resin ………………………..Application………………… | Check for sources of water contamination. Avoid over-spray. Improper spray techniques create excessive over-spray, droplets and flooding. Can be aggravated by long gel time and sagging. Do not allow over-spray to dry; keep a wet line. | |
| Sags and runs …… | Excessive gel coat ………. Spray techniques ………Low viscosity ……………. Mold wax …………….. | Apply 18 ± 2 mils, wet. Atomizing air is pushing and blowing the gel coat. Not enough styrene is being volatilized. Check viscosity and thixotropic properties. Overagitated. Material was reduced, but should not have been. Silicone content too high. Jarring the mold before gelation. | |
| Softness …………… | Soft gel coat film which be easily matted ………… | Incomplete cure of gel coat. Check catalyst levels, contaminants and film thickness. | |
| Splotches after demolding … | Solvent contamination ….. | Ensure that all solvent has been flushed out of spray equipment lines. For internal mix equipment, ensure that solvent flush line is not leaking. | |
| Splotches after parts are sanded and buffed— also referred to as ‘leathery,’ pebbly,’ ‘chicken skin’ ……..  | Over-spray ……………… Not maintaining a wet line …………………… Cure ……………………… | Do not allow over-spray to accumulate. Spray laps within five minutes. | |
Water spotting—see also fading ………….. | Usually caused by exposure with a combination of excessive heat and moisture ………Poorly cured gel coat ……. Certain chemical treatments such as chlorine and/or cleaners ………………………. Exposure of parts to moisture too quickly after fabrication ……………….. | Use only a product recommended for the particular application. Improper shrink-wrap. Use only a product (and recommended procedures) applicable to gel coats. Check for both over- and under-catalyzation. Misuse of these chemicals. Allow one week ambient cure before service. | |
| Yellowing of gel coat—gel coat yellows rapidly and unevenly when exposed to sunlight and/or heat and moisture; on ‘Weathering’ ……….
| Polystyrene/wax buildup on the mold which has transferred to the part during molding …..
Inadequate gel coat cure:
Contamination such as solvent, moisture, or oil …………………………………
Improper or unauthorized
Cold temperature during application……………………
Old material ………………….
Film cure inhibited by styrene vapors………………
Pre-release …………………
Excessively hot resin-rich laminates ………………
Resin tearing ………………..
Uneven gel coat film thickness ………………….
Cleaning the finished part with an alkaline cleaner ……………………………..
Holding gun too close to the mold ……………………. Spraying in one pass …… Insufficient atomization …. | Perform regular mold-cleaning program. Do not clean mold with styrene or used, dirty, or reclaimed solvent. Check catalyst (bad or old lot batch) and catalyst level. These contaminants will affect the gel coat’s cure. Do not add any material (other than the recommended
Do not apply gel coat at temperatures below 60ºF; Old material may be slow in gel and cure and will need adjustment. Consult a CCP representative. Provide adequate air circulation for ‘deep well’ areas
Most of the conditions which cause pre-release will Good laminating techniques must be followed. This Over-spray, excessive film build, flooding or contamination, Avoid flooding the gel coat or applying excessively Do not use any strong alkaline cleaner (such as ammonia or other cleaner having a pH greater than nine) for cleaning a gel coat surface. A weathered gel coat can be yellowed by such cleaners. Maintain proper distance. Spray in multiple passes. Gel coat must be atomized to fine particles. |
