Gelcoat fuselage Repair??? - RC Groups
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Feb 05, 2002, 01:20 AM
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Gelcoat fuselage Repair???

Does anyone know how to repair a gelcoat fiberglass fuselage. I am putting a BD-5 from Hobby Lobby together, and the gelcoat by the canopy area is chipping off. Any suggestions will be greatly appreciated.

Thanks in advance for the help.
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Feb 05, 2002, 08:53 AM
Balsa Flies Better!
Try a marine supply store- there are usually gel coat patch kits available. If it uses MEKP as a catalyst, be very careful with that stuff- it's nasty (no exposed skin, use gloves and goggles.)

Feb 05, 2002, 07:28 PM
Senior Member
cbosch_us's Avatar
Fiberglass products can be made from epoxy or polyester resins. Epoxy is stronger and more expensive. Many commercial products are polyester. Polyester comes in different types, the most common being:
* Casting resin - low viscosity for pooring into molds and casting figures, etc.
* Laminating resin - used for fiberglass layups. The surface will remain sticky after the resin has cured. This enables subsequent layers to bond to the previously cured layers.
* Finishing resin - contains a wax additive that floats to the surface and seals the resin from contact with air. This enables the resin to fully harden and not be sticky on the surface. This makes the resin easier to sand. If you want to add additional layups over cured finishing resin, all the surface wax must sanded away, or subsequent coats will not adhear.

Gelcoat is simply a pigmented polyester laminating resin designed to be the first coat applied to a mold. When you use it to repair a chip, the outer surface must be sealed from air contact or it will never fully cure - resulting in a tacky surface. This is easily done by covering the wet gelcoat with Saran wrap and letting it cure. You could do this, as Megowcoupe suggested, with a repair kit from a marine supply store.

Another method is to use pigmented epoxy instead of polyester. Epoxy is less sensitive to the cure problems associated with polyester gelcoat. You can get small tubes of resin pigments from a marine supply store. These pigments can be added to polyester or epoxy resin, thereby making you own gelcoat. Be careful how much pigment is added as too much can cause cure problems, even with epoxy. You don't need much. Use whatever epoxy you have available. I would not recommend the 5 minute variety, only because it does not give you enough time to work. A slower curing epoxy will also give the resin a chance to flow out and give you a better finish. Getting the colors to match exactly may be difficult.

Hope this helps,
Feb 05, 2002, 07:51 PM
Electric Coolhunter
Thomas B's Avatar
The least expensive method of repair would be to fix the chipped areas around the canopy sill with baking soda and thin CA or epoxy and microballons.

Carefully sand and blend in the repaired area with a bit of spot putty or spray primer.

Then carefully mask off the canopy sill about 1/4" to 1/2" back from the edge of the canopy, sand the gelcoat with 400 grit paper and add a bit of contrasting paint trim with an airbrush. A fun way to enhance the look of your model.

Or, you could carefully repaint all white areas on the fuse, blending in your repair that way.

Goign this route would not require you to buy a quanity of gelcoat material that you would never use up.
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Feb 05, 2002, 09:58 PM
Rehab is for quitters
LuckyArmpit's Avatar
As a former Universal Rundle employee whose job was repairs,
you need to find powdered silica or what we called cap-a-seal.
You mix this with gelcoat and throw in a little MEK (catalyst).
It sinks a tad when it dries but sands nice and smooth. Stronger
than hell. If you do it in some humidity, you need to add a little
ethyl acetate for it to cure.

Feb 05, 2002, 10:32 PM
Registered User
Andy W's Avatar
Lot's of replies.. here's another..
I just use a mix of epoxy and microballoons. Does the job, dries quickly, sands easily..
Feb 05, 2002, 11:57 PM
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crossup's Avatar
Thats Cabosil friend, not Cap-a seal. And its a fibrous silca product that does not increase volume as it thickens and is the most commonly used thixiotropic agent( antisag ingredient) . Microballons do increase volume but is a horrible thixiotropic agent(think of ball bearings held together with serup) , so its lightweight but LOVES to run and slump.

Also not to pick nits (but then again its a big nit) you DO NOT use MEK to promote resin. You use MEKP , methalethalketone peroxide as a catalyst.
Sorry about the spelling but the phonetics are correct

Another product not mentioned is PVA or polyvinylalcohol. This a used to spray over gelcoat or other resin products intented for inmold use or prone to amine blush. Promotes a hard surface cure for products requiring a sealed surface to cure. Commonly available at marine supply houses like West Marine.

Gelcoat (except neutral) is very opaque compared to colored resin(epoxy,or polyester/vinylester) so unless you are looking for a tranlucent effect, white gelcoat , colored to matched will look best


Originally posted by LuckyArmpit
As a former Universal Rundle employee whose job was repairs,
you need to find powdered silica or what we called cap-a-seal.
You mix this with gelcoat and throw in a little MEK (catalyst).
It sinks a tad when it dries but sands nice and smooth. Stronger
than hell. If you do it in some humidity, you need to add a little
ethyl acetate for it to cure.

Last edited by crossup; Feb 06, 2002 at 12:03 AM.
Feb 06, 2002, 01:06 PM
Registered User
Jim Ryan's Avatar
Getting back to the initial question about fixing a chipped BD-5 fuselage, there are easier and quicker ways to fix a small chip in a non-strength-critical area.

When I'm repairing a broken glass fuselage, one of my favorite materials for getting a really nice finish is good old Squadron white putty. This is a styrenic putty that can be applied with a spatula and allowed to dry. Because it's solvent-based, it shrinks some while drying, so you have to build it up a bit. But on the plus side, it's very convenient to use because there's no mixing required. Also, it dries to a non-porous surface that wet sands beautifully.

If I were repairing chips like Ivorz described, I'd make sure the gel coat is finished flaking (if necessary scraping the surface with an X Acto knife to get a solid stable surface). If it was crumbly, I'd saturate the damaged area with thin CA to stablize it. Then I'd apply white putty with a small spatula. After letting it dry thoroughly I'd wet sand it with 320 or 400 grit and then proceed with painting.

This is only for small cosmetic chips. I would not use this for large missing chunks.

Last edited by Jim Ryan; Feb 06, 2002 at 01:08 PM.