Using Epoxy To Seal Wooden Wings and Fuselage

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rotax618

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FGI here in Australia make a 2 part epoxy wood preservative, I used it when I built a VP1 and Flying Flea, after it is cured it is more or less inert to MEK and Dope etc.
 

Appowner

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My 2 cents worth from the RC world. Epoxy has the advantage of essentially being free of harmful fumes while we all know your dopes and other methods are not. Epoxy needs just basic ventilation.

The main issue I see with epoxy is it is far too easy to leave too much on the surface and it is HEAVY. Excess epoxy does nothing but add weight. For sealing wood I'd certainly use the thinnest epoxy I could find and squeegee the excess off. A layer of fiberglass is the method used in the RC world but care needs to be taken to ensure the glass is in contact with the wood surface for maximum benefit. And in RC the use of the glass is more for a ding resistant surface that resembles metal and to help minimize the epoxy needed. That weight thing again. A lot of guys will use the epoxy to just glue the glass to the surface and then fill the weave with something else.

While I haven't used it I have read up on the Peel-Ply method. It's used a lot in the RC world and basically it is just another way to minimize the amount of epoxy used. But it also leaves a near perfect ready for paint surface. When done right! Here's a link to some info on it from one vendor: Peel Ply Link

Thinning epoxy can be done but depending on who you talk to it impacts the cure time and the strength. I use denatured alcohol to thin it while a lot of other things will also work. For me it's the fume thing again. And I use the best alcohol I can find and only when something better is not available, like a good finishing resin.

The mistake I think most people make here is adding too much alcohol. I've seen people report using as much as a 50/50 mix of epoxy and alcohol but I have never needed so much. I find it takes very little to thin the epoxy the key I believe to be a thorough mixing. Granted I use very little epoxy at a time but I literally use just a few drops of alcohol for an ounce of epoxy. Mix well and then add more alcohol if needed.

Another option are heat lamps. Depending on the size of the work. Heat lamps will do a couple of things for you. They will initially thin the epoxy for best penetration followed by shortening the cure time.

For my purposes I keep several types of epoxy on hand. For general model construction I like a slower setting epoxy with a working time around 20-30 minutes. I also keep a finishing resin around which has a working time of an hour. I avoid the faster curing epoxies with a 15 minute work time being the fastest I'll use. For my purposes the brand really doesn't matter and I can be found buying my epoxy at the local craft stores (dedicated hobby shops are few and far between) but I have used West Systems and try to keep it on hand. I imagine for you guys a quality brand is a bit more important. :)
 

TFF

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Thinning epoxy for RC for me has been mostly for fuel proofing structure. I have never thinned it to glass something or structural. I just use thinner types of epoxy when glassing. That usually means I’m building something specific and not general RC knock around. The last few fuel proofings have been with the dregs of my Clear Coat.
 

BJC

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Epoxy has the advantage of essentially being free of harmful fumes while we all know your dopes and other methods are not. Epoxy needs just basic ventilation.
That could be misleading. I encourage everyone to research the precautions for the specific chemicals being used. (Not all “epoxy” is the same.) Start with the safety data sheet. Example of relatively safe T-88 here https://woodworker.com/pdf/115-283_MSDS.pdf

In addition to the hazards listed, I have noted that some of my friends who have used it for many years have become irascible old coots.


BJC
 

Pops

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I get a reaction breathing the fumes from T-88. I have to have a fan behind me and the room ventilated. In my hanger workshop I open a patio door on the upwind side and a garage door on the down wind side. Make a good airflow across the hanger.
 

speedracer

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Feb 4, 2020
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My 2 cents worth from the RC world. Epoxy has the advantage of essentially being free of harmful fumes while we all know your dopes and other methods are not. Epoxy needs just basic ventilation.

The main issue I see with epoxy is it is far too easy to leave too much on the surface and it is HEAVY. Excess epoxy does nothing but add weight. For sealing wood I'd certainly use the thinnest epoxy I could find and squeegee the excess off. A layer of fiberglass is the method used in the RC world but care needs to be taken to ensure the glass is in contact with the wood surface for maximum benefit. And in RC the use of the glass is more for a ding resistant surface that resembles metal and to help minimize the epoxy needed. That weight thing again. A lot of guys will use the epoxy to just glue the glass to the surface and then fill the weave with something else.

While I haven't used it I have read up on the Peel-Ply method. It's used a lot in the RC world and basically it is just another way to minimize the amount of epoxy used. But it also leaves a near perfect ready for paint surface. When done right! Here's a link to some info on it from one vendor: Peel Ply Link

Thinning epoxy can be done but depending on who you talk to it impacts the cure time and the strength. I use denatured alcohol to thin it while a lot of other things will also work. For me it's the fume thing again. And I use the best alcohol I can find and only when something better is not available, like a good finishing resin.

The mistake I think most people make here is adding too much alcohol. I've seen people report using as much as a 50/50 mix of epoxy and alcohol but I have never needed so much. I find it takes very little to thin the epoxy the key I believe to be a thorough mixing. Granted I use very little epoxy at a time but I literally use just a few drops of alcohol for an ounce of epoxy. Mix well and then add more alcohol if needed.

Another option are heat lamps. Depending on the size of the work. Heat lamps will do a couple of things for you. They will initially thin the epoxy for best penetration followed by shortening the cure time.

For my purposes I keep several types of epoxy on hand. For general model construction I like a slower setting epoxy with a working time around 20-30 minutes. I also keep a finishing resin around which has a working time of an hour. I avoid the faster curing epoxies with a 15 minute work time being the fastest I'll use. For my purposes the brand really doesn't matter and I can be found buying my epoxy at the local craft stores (dedicated hobby shops are few and far between) but I have used West Systems and try to keep it on hand. I imagine for you guys a quality brand is a bit more important. :)
Peel ply does NOT leave a "near perfect, ready to paint surface." Pretty much the opposite because of the weave. Like the peel ply link says, the purpose of it is to leave a rough surface for secondary bonding after cure. Even then, most composite builders (me included) also sand it with 80-40 grit to rough it up even more "just to make sure" before secondary bonding. Peel ply does save a little weight, but very little. The best method I've found (besides vacuum bagging) is to press paper towels onto an overly epoxy rich layup (before the peel ply goes on) to remove excess epoxy.
 

David Muldoon

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Dec 14, 2020
Messages
4
Thanks for the replies to everyone, you have helped me move in a direction I hadn’t given much thought to.

Looks like I have a bit more reading to do, but I keep seeing EV 400, System Three Clear Coat or a thinned West System as an epoxy sealer used by many, in various places as I search for info.

My tail feathers are covered with 4 layers of Varathane Premium (water based), Outdoor professional grade polyurethane, over top of that will go an Oratex covering.

For the wings, it looks like EV 400, then they will be covered in Dacron and the Stewart System used for them and the forward fuselage. The aft fuselage, I’ll give some thought to as I want to keep the weight forward (the Boredom Fighter has a very restrictive CG range for my size and weight), just in case I inadvertently, overdo the paint work.
 

TFF

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17,932
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Ev 400 is designed to be able to top other varnishes. I put Clear Coat over a previously coated wing too. Some others may not stick to a one part, so test before putting a bunch of time in.
 

Geo

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Joined
Feb 14, 2021
Messages
3
I seal my wood with stitts poly brush! After fabric covering the first coat of poly brush wetted the poly brush on the ribs giving it extra adhesion. Mixing hardware store varnish and fabric materials are a deadly combo. the final FAA report on Steve Wittmans accident was a repair was made mixing chemicals from two different covering processes. the same goes for these guys that paint a plane with house paint, you can't safely repair the fabric unsafe adhesion. a couple coats of poly brush then poly spray to prevent UV damage.......and the new one will be the same. Geo.
 

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