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Fiberglassing wing panels together

Old 04-28-2008, 09:10 AM
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Clay Walters
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Default Fiberglassing wing panels together

Reckon I'm just a bungler. Because I wasn't satisfied with the fit-up of two wing halves I decided to reinforce the joint with a wrap of fiberglass tape and finishing resin. Having read that finishing resin was better because it saturated the cloth better and sanded better than standard epoxy I'd hoped to be able to sand it smooth and hopefully be slightly noticable under the monokote.

I spread a thin lay of resin down, lay cloth on it, and used the brush to gently work the cloth into the resin. Then I followed with a squeege with a dummy credit card just like I'd read so many times about doing. Trouble was, I had a number of spots that just didn't wish to stay down. Rolled the wing over and did the other side which went much better and then back over to work down the "bubbles". Finally everything seemed to be setting smooth and straight so I turned off the lights to let it cure up.

Next morning I discovered each and every one of those "bubbles" managed to come back up and no amount of sanding other than sanding it all off is going to clear the mess I've got. I don't even know if monokote will stick to the stuff when smooth much less when bumpy. I used an exacto knive to remove the bubbles and have sanded till I'm sick of it. This things gonna look like a wart covered pig presuming it will cover at all.

And I don't find the finishing resin much easier to sand than regular 30 minute epoxy.

Sign me disgusted,

Clay
Old 04-28-2008, 10:08 AM
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Campy
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Default RE: Fiberglassing wing panels together

The reason you have bubbles is most likely the surface underneath had something contaminating it (finger oil, etc ). For future reference, before sanding go over the area with a DAMPENED (not wet) with alcohol. After the alcohol dries, sand the area, then remove the dust by using an air hose, brushing it off, etc. THEN go over the area again with a cloth dampened with alcohol.

The suggested way to do a re-enforcement of the center section is: Put down a 6" - 8" wide strip of 2 oz fiberglass cloth, then put your resin on the cloth and work it into the cloth (get rid of the excess using rolls of toilet paper or an old credit card or a combination there of). Do one side at a time AND LET IT DRY BEFORE DOING THE OTHER SIDE. After you have done both sides, lay a strip of 2 oz cloth that is 2" NARROWER than the first piece over the 1st piece and apply the resin and remove the excess. This time take a piece of Saran wrap and CAREFULLY put it over the resined area and GENTLY press it onto the resin and smooth out any wrinkles/bubbles. Secure it down with some masking tape. When dry, repeat this for the other side.

The Saran wrap makes the drying time a little longer, however when you peel the Saran wrap off the surface will be smooth and require little, if any sanding. Go over the area with a cloth DAMPENED with alcohol to remove any wax. Now use some lightweight filler to feather the edge of the glass into the wood and the edge of the 2 pieces of fiberglass together. This will provide a smooth, barely detectable re-enforcement.

In your case, I suggest filling the bubble holes with light weight filler and sand everything smooth. Then apply a second piece of 2 oz fiberglass cloth as described above and make sure you use the Saran wrap over it and finish as described above.

Finishing resins typically leave a wax residue on the surface when it dries.
Old 04-28-2008, 11:39 AM
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Clay Walters
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Default RE: Fiberglassing wing panels together

Thank you for a very thorough explanation Campy. I can see where doing only one side at a time was the smart thing to do now. And the saran wrap idea sounds good too. I did sand the area first but didn't wipe with alcohol first.

Will explore the extra steps you suggest but being a small plane I'm concerned about any additional weight. Its the cosmetics that bother me the most.

Can you advise whether or not monokote will stick to this?

Thanks again,

Clay
Old 04-28-2008, 11:53 AM
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Tango Juliet
 
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Default RE: Fiberglassing wing panels together

Campy - Thanks for that post. I've been building off and on for about twenty years now, and still haven't been able to get a "glass" smooth wing joint with fiberglass and epoxy. I'll definitely try your method the next time. BTW, what is the real difference between using epoxy and finishing resin? I've never really known the difference.
Old 04-28-2008, 12:13 PM
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Default RE: Fiberglassing wing panels together

ORIGINAL: TJR1

........what is the real difference between using epoxy and finishing resin? I've never really known the difference.
Finishing resins don't form strong molecular links as they cure, they are not strong enough for a laminating epoxy or a structural bond. they do form a smooth film as they cure and they make an excellent fuel proofing and they are good for bonding fiberglass to wood and they also paint fairly well.
Old 04-28-2008, 01:02 PM
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Default RE: Fiberglassing wing panels together

Thanks.
Old 04-28-2008, 06:44 PM
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j.m.
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Default RE: Fiberglassing wing panels together

don't use compresed air to clean the dust off. use a vacuum cleaner. Most air compressors put lubricating oil into the air to keep tools working good. Also, compressed air is going to blow every single particle of water that is in the air onto your wing. Not ideal.

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