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 |
| Air Bubble
| Air pockets | Check rollout procedures. |
| Alligatoring—a wrinkling of the gel coat, resembling alligator hide
Before laminating—
After or during lamination, or a second application of gel | Raw catalyst ——– Solvent ————– ‘Cured’ over-spray—- Thin gel coat ——- Insufficiently cured gel coat————-
| Check for leaks or over-spray. Do not reduce with solvents. Check for contamination. Maintain a wet line. Use a minimum of 12 mils, wet. Discontinuous gel coat film. Catalyst level too high or too low. Temperature too low. Gel time too long. Time between coats or lamination insufficient. Moisture or contamination in the mold. |
| Bleeding—one color shows on another, typically when color striping——————–
Laminate Bleed (cosmetic problem only)———————- | Striping gel coat sagging over ‘cured’ gel coat —————-
Monomer in laminating resin —— Gel coat back side cure —————– | Check sag resistance of ‘striping’ gel coat. Spray stripe coat as soon as possible. Spray thin film of stripe color over the ‘wet’ base coat.Check for excessive monomer in laminating resin.Change gel coat. |
| Blisters —
Appear shortly after part is pulled, especially when put in sun——-
Appear after part in field ——————
Water blisters ——- | Unreacted catalyst or under-cure ——
Solvent, water, or oil Air pockets ——— Unreacted Solvent, water, or oil ——————- Various ————- | Check percent catalyst, catalyst over-spray, mixing, and leaks. Check air lines, material, and rollers. Check rollout. Check catalyst levels and distribution, film thickness— 18 ± 2 mils. Check air lines, materials, and rollers. See Part Four, Chapter VII.5 on ‘Blisters and Boils’ tests. |
| Chalking (gel coats will oxidize/chalk over an extended period of time; degree of chalking is related directly to the environment
Dry, chalk-like appearance or deposit on surface of gel coat (premature) ——— |
Cure —————-
Contamination —-
Insufficient
Poor mold |
Under- or over-catalyzation, producing incomplete cure. Check air lines, material, and rollers. Check catalyst level, film thickness, water and solvent contamination. Surface soil picked up from atmosphere.
Wipe buffed area with solvent rag. If gloss remains, area is okay. If gloss dulls down, part needs more buffing.
Reduce sanding and buffing requirement on parts by keeping molds in good condition. |
| Checking (mud cracking)— Single or groups of independent or cres- cent-shaped cracks —- | Poor integrity of the gel coat film — | Trapped vapor or incompatible liquid which blows through the gel coat film on aging. Check catalyst level. Check for water, solvent, etc. Chemical attack. Temperature extremes. |
| Craters—while spraying | Chunks in the gel coat —————–Equipment ——— | Dirt in the gun or material. Material old and starting to gel; rotate stock. Strain (filter) the gel coat. Clogged gun (clean). Improper atomizing air setting (too low). |
| Cracks —
Spider cracks radiating out from a central point or in circles (reverse impact) ————— Stress cracks (cracking in parallel lines) ——— |
Impact from laminate side ——
Excessive gel coat film thickness —–
Mold mark ——— Impact ————–
Stress due to
Mold mark ——— |
Check on handling and demolding procedures. Caution people about hammering on parts. Use a mil gauge and do not go over 24 mils.
Defect in the mold. Be careful.
Excessive gel coat thickness. Laminate too thin.
Defect in the mold. |
| Delamination— In spots ————–
Large area ———– | Contamination
Gel coat too fully cured
Contamination —-
Unbalanced |
Check for dust, solvents, moisture, catalyst getting onto the gel coat surface. Excess mold release wax floating through to the gel coat surface, creating areas that will not adhere. Check for high catalyst level. Letting the gel coat cure too long, such as overnight; skin coat, rather than leave on the mold for long periods of time. Excess mold release wax or wax in the gel coat. Solvent wiping, then waxing (around taped off areas), Dry fiberglass. |
| Dimples—in the gel coat surface
| Contamination
Other | Check for water, solvent, or improperly mix catalyst. Over-spray. Seedy resin. Excess binder on the glass mat.
Thin laminate or gel coat. Very dry laminate. Pin air entrapped. Post-curing of the laminate. |
| Dull gloss—on the gel coat— When part is pulled –
When and after part is pulled ————– |
Rough mold ——–
Mold buildup ——
Polystyrene buildup —
Dirt or dust on mold —
Solvent or water —
Raw catalyst ——-
Rough PVA or wet PVA —————–
Insufficiently cured gel coat or laminate — |
Polish out mold.
Wax and buff with cleaner. In most instances, what is called wax buildup is actually polystyrene buildup and should be treated as such.
Sand or scrub with brush and strong solvent; read precaution on solvent before using. DO NOT USE STYRENE.
Clean the mold. It is best to clean in the spray booth just prior to gel coating. Time span should be as short as possible between cleaning and gel coating. Use a tack rag. Check for solvent or water. Drain water traps regularly. Start catalyst flow from gun away from the mold. Only catalyzed gel coat should be sprayed into the mold.
Check spray technique.
Correct excessive or insufficient catalyst level in gel coat and laminate. Wait longer before pulling.
Check for low temperature (minimum of 60ºF). Check for contamination: water, air or solvent. |
| Dull or soft spots—at random ————— | Gel coat uneven —
Catalyst poorly mixed into either gel coat and/or laminate ——
Trapped solvent in gel coat and/or laminate ————
Trapped water in gel coat and/or laminate. catalyst — | Poor breakup; use three passes.
Mix catalyst thoroughly or make equipment
Check cleaning procedure. Check catalyst level with equipment using solvent reduced catalyst.
Drain lines and correct the problem. Confirm correct catalyst concentration. |
| Fading—see also water spotting ——- | Poorly cured gel coat —————–
Improper cleaners or chemicals——– | Check catalyst levels and film thickness (18 ± 2 mils).
Do not use strong alkaline or acidic cleaners. |
| Fiber pattern and distortion—in parts
|
Insufficient cure —
Transferred from
Glass cloth ———
Woven roving ——
Gel coat too thin — High exotherm of laminate ———— |
Correct excessive or insufficient catalyst level in gel coat and/or laminate. Wait longer before pulling, Do not pull while laminate still has heat. Check for low temperature. Check for contamination by water, oil, or solvent.
Refinish mold.
Too close to the gel coat. Should have two layers of cured 1.5 oz. mat or equivalent chop between gel coat and cloth.
Too close to the gel coat. Should have three layers of cured 1.5 oz. mat or equivalent chop between gel coat and woven roving. Use 18 ± 2 mils, wet.
Cure laminate more slowly. Laminate in stages. Use lower exotherm laminating resin. |
| Fisheyes
| Water, oil, or silicone contamination —–
Dust / dirt on mold —
Gel coat film too thin –
Low viscosity | Drain air lines. Check mold release wax. Excess and/or fresh coat of wax is worse.
Check lubricating materials used within the equip- ment. Use tack rag.
Use 18 ± 2 mils in three passes.
Old material—rotate stock. |
