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Old Sep 09, 2012, 09:13 PM
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FlyingW's Avatar
Long Valley, NJ, USA
Joined Dec 2001
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Question
Can 30 Minute Epoxy Be Thinned and Still be Strong?

I want to wrap a 2" fiberglass tape around the wing center joint of a balsa-covered wing.

I do not have any Sig Finishing Resin left, but I do have 30 minute epoxy.

Can the 30 minute epoxy be thinned to help it soak into the wood a bit, and still cure strongly?

If yes, what can I use to thin it?

Please advise.

Thanks,

Paul
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Old Sep 09, 2012, 09:20 PM
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amherst,nova scotia,canada
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Heat will seriously thin it but cure will speed up substantually. You could try this on a scrap of material first with a covering shrinking gun or hair dryer.
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Old Sep 09, 2012, 09:39 PM
pilot
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United States, AZ, Prescott
Joined May 2011
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.com has excellent thin resin. Finishes beautifully

If you do thin epoxy use denatured Alcohol I'm told instead of isopropyl. Look for 99%
Check with fiberglass supply.com. They have a beautiful low viscosity resin, and great glass cloth as well. Also check with BVM for fantastic aerospace grade resins in different viscosities
. Best to you
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Old Sep 09, 2012, 10:06 PM
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Hawaii
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Apply the FG with a light spray of Spray77, then apply the epoxy, heat, & remove excess with a CC.
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Old Sep 09, 2012, 11:53 PM
pilot
Props's Avatar
United States, AZ, Prescott
Joined May 2011
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.com has excellent thin resin. Finishes beautifully

If you do thin epoxy use denatured Alcohol I'm told instead of isopropyl. Look for 99%. I am going to surmise then that 200 proof ethanol would work very well and is less toxic to have around.

Before all that, I'd consider getting resin of the preferred viscosity, and use thinner as a plan "B"

Best to you
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Old Sep 10, 2012, 10:47 AM
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Old Sep 10, 2012, 11:39 AM
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Florida
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By far the best, just put on as thin a coat as you can and then gently heat with a heat gun. You will see the epoxy suddenly flow out and completely wet the cloth. Yes, cure time is lowered a lot which is usually an advantage. Any time you thin with a thinner you will weaken the bond of the finished product.
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Old Sep 10, 2012, 06:30 PM
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amherst,nova scotia,canada
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Quote:
Originally Posted by Rodney View Post
By far the best, just put on as thin a coat as you can and then gently heat with a heat gun. You will see the epoxy suddenly flow out and completely wet the cloth. Yes, cure time is lowered a lot which is usually an advantage. Any time you thin with a thinner you will weaken the bond of the finished product.
Now i remember. Thinning is detremental to the molecular link up of the epoxy resin I think I remember. Again nothing is really free. The heat approach works very well for me. The thinned resin grips into pores better perhaps as well.
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Old Sep 10, 2012, 07:30 PM
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I guess I just make strong wings. I've been thinning epoxied center-sections since the 70's, starting with HobbyPoxy Formula II and alcohol, and I've had precisely one wing fold -- and that was with full-throttle, maximum deflection, outside loops.

CD
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Old Sep 11, 2012, 03:17 AM
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The 'Wack, BC, Canada
Joined Oct 2002
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Using epoxy for a center joint band of glass is heavy overkill anyway. Regardless of whether it's thinned with alchohal or heat the resulting wrap of glass and epoxy is hellishly stronger than the surrounding wood. So by all means use which ever you want.
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Old Sep 13, 2012, 10:29 AM
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FlyingW's Avatar
Long Valley, NJ, USA
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Thanks everyone for your ideas and experience. I'm scared away from chemically thinning the epoxy after reading most of the entries (except for outside loop-man CD). I tried the heat gun test on a balsa scrap and I did get some wood-soaking.

For the final work I have decided to go with finishing resin (ordered) and a three-inch glass tape. The wing is for a Four Star 120, and based on the center join structure, I will feel more confident in having the 3/32" balsa center section sheeting contribute to the join strength.

CD - Folded one once too - a Jensen Ugly Stik - flying too hard.

Thanks all and be well,

Paul
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Old Sep 20, 2012, 08:50 PM
SHAG
Joined Nov 2008
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I mix my own fuel ( FAI ) and when I want to reinforce something I use a little methonal to thin the epoxy just enough for brushing and apply before and after laying the glass, if
ayou want to save your throw away brush, use methonal.

Paul W

P.
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Old Sep 20, 2012, 09:21 PM
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So methonol is simular to actone for clean up then? If ever again I build another nitro or diesel plane. It is still a possibility at least in my mind. The world is not totally electric yet.

I will still fuel proof the engine compartment by applying epoxy resin and some heat. I want to seal the area without excess weight. Kind of spread a smaller amount further in coverage with it and smooth the resultant finish without sanding.

Actually I always did it this way after epoxy resin got so popular and easy to access. Lost too many planes by fuel soak. Until I discovered that laquer thinner would soak and lift the oil content out of the wood if you were patient enough. Dries out of the wood very fast and does not warp it.

. The proof the cure of the molecular bond is weak with epoxy Is any indication of an incomplete cure I imagine. Might be wrong though. The most common issue is not weighing your resin and hardner before mixing though. Guessing is not really good enough with epoxies. It may get you by most of the time though.

A digital gram scale that I find extremely usable is five dollars delivered out of the orient. If i had a dollar for every thing I either figured out or someone was kind enough to pass the information along to me over the many years. I certainly would be less than rich but it would be at least some money.

For the younger guys that always had the web it should have been easier enough really . Having so many options today versus long ago is good. It does not make the hobby more fun though in my opinion. A fifty cent three foot wingspan easybuilt kit,razor blades, sandpaper,glue and straight pins was about it when I first started 63 years ago.

Dope and tissue or silkspan or silk was it for coverings until plastic covering came along. Dope and silk added real strength to your build in my opinion compared to plastic coverings.
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Old Sep 22, 2012, 02:18 PM
wood is good
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United States, CA, Marina Del Rey
Joined Jun 2012
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Use the proper epoxy resin and you won't have to contaminate it with experimental thinners and solvents which can only reduce its mechanical properties, or worse.

W.E.S.T System or Smith's Penetrating epoxy would be vastly superior choices. Keep surfaces clean and dry and avoid the use of any product which will hinder the epoxy's ability to penetrate (such as the spray contact cement suggested).
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Old Sep 23, 2012, 02:20 PM
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FlyingW's Avatar
Long Valley, NJ, USA
Joined Dec 2001
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Used ZAP finishing resin and it worked great.
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