Fiberglass/Gelcoat Question.

[Earley Motorsports]

Hi all. I have a question on whether sanding the gelcoat down to the fiberglass and reapplying the gelcoat will fix spider cracking. I have done plenty of fiberglass repairs in my day but don't have much experience in gelcoat so any help/advice would be greatly appreciated. I want to do this right due to the rarity of the car. Thanks in advance.

[Bobsy SR 6]

Graham
Stress cracks in the gel coat can be caused by several factors. In an older piece (unless it has been recently refinished) the cause is usually due some form of stress to the area surrounding the cracks. This could be impact or flex or some other load, the gel coat is less,flexible than the under laying fiberglass.

If the cracks are due to impact, however minor, the substrate will need to be repaired first. If the under laying cause is flex, than the area will need to be reinforced. Sometimes however the cracks are due to age as the fiberglass under the gel has a different coefficient of expansion than the gel. The best way to fix surface cracks is to die grind the cracks down into the fiberglass top layer only. Then fill the area with epoxy resin mixed with micro balloons.( A product available from most plastic supply houses or boat repair centers. This product is glass bubbles used to thicken the resin into a filler consistency.. Epoxy resin will bond to all polyester resins as well as just about anything else. Polyester resin is what was most commonly used back in the day)

Sand and smooth the repaired area just like normal body work. When spraying gel coat you will find the viscosity is rather thick, which is normal. Avoid reducing the gel too much as the finish will be affected. Due to the viscosity the finish wil have an orange peell appearance which is normal and will require block sanding then buffing to restore luster. After spraying the gel coat you will need to spray a product called PVA (polyvinyl alcohol) which will seal the oxygen away from the surface allowing the gel coat the completely harden. Once the gel cures the PVA can be washed off with water.

After 27 years in the marine industry I managed to pickup a few things Good luck!!

Cheers
Tom

[Earley Motorsports]

Excellent advice there Tom. Thank you. That is what I was needing to know.

[DanW]

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[DanW]

Tom is on the money with his advice. If there is structural damage, the underlying fabric is cracked or broken, you can grind away the damage from behind and some from above. Then lay up woven fabric for strength behind the area and glass mat for the exterior. The glass mat will not "print through" its texture to the paint. The woven fabric will. I salvaged a Lotus Elan boot lid that someone had sat upon and created a large spiderweb across the entire piece. I sanded it with a 40 grit belt sander til it was very thin. I laid up 1 oz. glass mat, added a fiberglass sealer then Evercoat hi-build primer before sanding and color. The cracks never came back.

The West system expoxy resins are expensive but the results are very consistent. Do-overs suck. If it happens, grind it off and do it again.... Their how to videos are very helpful if you are just starting out.

If you find the West materials too expensive, the marine vinyl ester resins are very good, just be mindful surface prep with 25-40 grit, enough ambient temperature (60F minimum) and catalyst use. I have used them with great results.

[Earley Motorsports]

More great stuff. Thank you. This is just old (1967) and has never been raced and if so very gently. It is the body on my LeGrand MK6. No crash damage whatsoever.