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  1. #1
    tfarmer96's Avatar
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    5 minute epoxy vs. 30 minute epoxy?

    IS there a significant difference in the strength of 5 minute epoxy vs 30 minute epoxy. If the working time were not a factor are they the same?
    Spitfire Brotherhood #2
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  2. #2

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    IMO--NO.

    I think that 30 minute will soak into the wood pores and give a stronger bond.

    5 minute dries so fast that it won't soak into the pores a whole lot before it sets.
    Airplanes have expiration dates. Its just not printed anywhere on them.
    Im not really an airplane pilot; but I did stay at a Holiday Inn Express last night.

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    As stated above 30 minute will soak further in the wood and give a MUCH stronger bond. Where your inst. manual states to use 30 minute USE IT. The most important place to use 30 minute is while joining wing halves. THERE IS A BIG DIFFERENCE

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Additionally, 5 min epoxy is not fuel proof -- never use it in a strength-critical application where it can be fuel contaminated.

  5. #5
    RCU Forum Manager/Admin RCKen's Avatar
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    As the others have said, 30 minute epoxy is stronger. The longer cure time allows it more time to soak into the wood and bond with the wood. This longer times makes the bonds stronger. I very rarely use 5-minute epoxy when I'm building. In fact, the only thing that I can think of off the top of my head that I use 5-minute epoxy for is on the back of blind nuts to secure them in place. I use 30-minute epoxy for everything else.

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  6. #6
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Twice, I have been given a gift of a glue set which contained (among other things) a set of 30-min epoxy, a set of 6-min epoxy, sandpaper, sanding blocks, mixing cups, etc.

    I gave away one of the sets of 6-min epoxy, and the oither is still sitting in my shop unopened for over a year.

    I just won't use the stuff.
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  7. #7
    tfarmer96's Avatar
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Just wanted to make sure befor i epoxyed my wings together.
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    All of the above comments are correct but they missed one BIG fact...
    When they say that this is 5 Minute epoxy ... the clock is running from the moment that you add the hardener.

    I saw a local fellow use this stuff on a wing, it set up so fast that he couldn't get the two wing halves fully seated (he never admitted that he was slow ) and he flew the plane with a 1/4" gap between the wings halfs.

    The 30 minute epoxy gives you plenty of time to work, PLUS it is stronger etc.
    It's Time to Kick the Tires and Light the Fires!

  9. #9

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Yes, slower setting epoxy is stronger but not because it soaks into the wood farther. It is because the molecular chains formed as the epoxy cures (it does not dry, it chemically cures) are longer hence stronger. How far it soaks into the wood is a function of its viscosity which is a function of temperature. Warm the mix to get better penetration if that is what you think you need. Just remember that heat will also accelerate the cure rate.

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Hi!
    It's not stronger!!!
    Not a stronger bond in our applications (balsa and ply).
    I use CA glue (Flash) ! Much better!
    Thats just my 30 years experience.

    Regards!
    Jan K
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  11. #11
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    I'd agree with Jaka that in our applications, there isn't a significant diff in bond strength between epoxies and CAs. I like and use both, but epoxy is still my overall fave adhesive because of how versatile it is (that and I mainly build composite airframes.)

    Technically, most 30 minute epoxies are a bit stronger than 5's due to the longer cure time, but I believe it is only like 10% or something in that range. Heat is another factor in cure strength as most epoxies will cure harder if cured under heat, generally in the 150F range, but it does vary and a quick blast from a heat gun won't do anything. The epoxy has to be baked for hours at this temp and the heat must be applied during the gel stage all thru till final cure.

    The main diff between 5 and 30 is work time as pointed out in previous posts. It is difficult to set parts with 5 minute epoxy and gain good penetration, which can result in a weak bond. But this isn't the fault of the epoxy’s strength. The epoxy is fine, it is the bond that fails. You can add heat to lower the viscosity which will greatly increase penetration, but it also greatly decreases working and cure time and if too much heat is applied, the epoxy can blister, which will weaken the joint. One of the best ways to ensure good penetration and hence a good bond is surface preparation, i.e. sand and clean.

    When all is considered, I wouldn't be afraid to trust my planes to all 5 minute epoxy as the strength is more than sufficient. However, in practice this isn't feasible as the 5 minute stuff is difficult to work with because of the rapid cure times. For that reason, I only use 5 minute for small items that I can align quickly. I also find 30 minute too fast sometimes, especially if I added fillers to the epoxy which tend to cause it to kick quickly. For example, 30 minute epoxy at room temp with the right fillers will kick in about 5 minutes. In those situation I often use a very slow cure mix, like a 2 hour formula.

    Cheers.

  12. #12

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    I use 5 or 6 minute for things like tri stock on the LG mount or tri stock behind the firewall. Sometimes, I'll use quick cure epoxy on a servo rail if I don't have any thick CA.

    I use 30 minute for actually glueing the firewall in. 30 minute on the LG mounts, wing joint, wing hold down mounts. Also for glueing the horizontal stab and vertical fin onto the fuse.

    When fiberglassing the center joint on a wing, I'll use 30 minute and thin it with a couple drops of denatured alcohol. Just a couple drops (5 or 6) in a mixing cup with about 2oz of epoxy--a little goes a long ways. Spreads easily with an epoxy brush or credit card.

    I use 2hr finishing resin for fuel proofing my firewall and tank compartment. It takes 24-36 hours to fully cure--but it turns out smooth and is fuel proof enough for my needs. I try not to slop fuel all over the place and always drain my tanks after flying. Paint it on with a brush and let it sit overnight. The only problem is that it's so thin that it runs. If your doing the firewall, you need to paint it on and then stand the plane on it's tail while the epoxy cures or else it will run all over the place. Best thing to do is fuelproof the firewall right before you retire for the night. By the next morning--it's cured enough to mount your engine.
    Airplanes have expiration dates. Its just not printed anywhere on them.
    Im not really an airplane pilot; but I did stay at a Holiday Inn Express last night.

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Hi, does it matter which 30 minute epoxy you use or all they the same?
    thank you
    Yup; I\'m the guy the hobby shop warned you about...

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    tfarmer96's Avatar
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    I just got my wings put together and you guys are right there is no way i could have got it done right with 5 minute epoxy.
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  15. #15

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    ORIGINAL: planechucker

    Hi, does it matter which 30 minute epoxy you use or all they the same?
    thank you
    The epoxy that you buy from Tower or the local hobby shop is all about the same.

    If you start buying epoxy at home depot or safeway--then all bets are off.

    You can buy bulk epoxy from Tower on their Stock UP pages.

    Bulk Epoxy:
    http://www.towerhobbies.com/products/stockupsale.html
    Airplanes have expiration dates. Its just not printed anywhere on them.
    Im not really an airplane pilot; but I did stay at a Holiday Inn Express last night.

  16. #16
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    RE: 5 minute epoxy vs. 30 minute epoxy?


    ORIGINAL: britbrat

    Additionally, 5 min epoxy is not fuel proof -- never use it in a strength-critical application where it can be fuel contaminated.
    I've been using it on firewalls for 6 years without a single problem. Maybe you use a cheap brand.
    Had I known that flight was going to cost me $100 per second, I wouldn\'t have flown 30 seconds!

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Hi, I'm Paul.
    I'm learning from these posts, I ordered a kit to assemble and they (Tower) have CA thin, med, and thick as well as epoxy 6 and 30 min., The kit instructions would probably tell me what to use and where correct? The kit won't be here for a few days yet and I wanted to order what I need to assemble it. Thanks for being patient with dumb questions but I just started into this and want to learn correctly without screwing things up on the get go.

    Paul
    Yup; I\'m the guy the hobby shop warned you about...

  18. #18

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    RE: 5 minute epoxy vs. 30 minute epoxy?

    i hate mixing epoxy... especially when it is meant to be 30 minute epoxy but sets off in 5 minutes and you are just about to join your wing halves together!
    yep, i am an idiot... but i used a stopwatch (from the moment the first drop of hardener was added to the cup) and it got to 5 or 6 minutes and started to set off...
    so i have two wing halves with dried epoxy on them and a joining brace that needs a real good scrape clean. I didnt bother trying to get the wing halves together... i am sure it would have been disastrous. at least this way, i can clean it all up and start again!


  19. #19
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    ORIGINAL: planechucker

    Hi, I'm Paul.
    I'm learning from these posts, I ordered a kit to assemble and they (Tower) have CA thin, med, and thick as well as epoxy 6 and 30 min., The kit instructions would probably tell me what to use and where correct?
    Usually the kit will tell you, but sometimes all the kit says is use CA or Epoxy. In my shop I usually keep thin and thick CA and 15 and 30 minute epoxy. I don't even bother with 5 minute epoxy, there's not enough working time. I also keep a bottle of microbaloons in case I need to fill gaps. I use the thin CA for balsa to balsa joints where the pieces are already in position, the joint is tight, and I can wick the glue into the joint. I use the thick CA for joints between balsa and plywood, but only when I am sure I can get the parts into the correct position very quickly. For joints subject to significant stress, such as firewalls, the wood that serves as landing gear mounts, or where I know it is going to take me a few minutes to get the alignment right, such as gluing the tail surfaces to the fuselage, I get out the epoxy. If I think the joint is going to take huge stresses, such as the transom on my tunnel hull outboard boats, I will supplement the glue joint with a layer of fiberglass cloth glued in with epoxy. Occasionally I make a paste by mixing cut up fiberglass cloth and epoxy.
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  20. #20
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    ORIGINAL: mikedsilva

    i hate mixing epoxy... especially when it is meant to be 30 minute epoxy but sets off in 5 minutes and you are just about to join your wing halves together!
    yep, i am an idiot... but i used a stopwatch (from the moment the first drop of hardener was added to the cup) and it got to 5 or 6 minutes and started to set off...
    so i have two wing halves with dried epoxy on them and a joining brace that needs a real good scrape clean. I didnt bother trying to get the wing halves together... i am sure it would have been disastrous. at least this way, i can clean it all up and start again!

    Yup, no fun, eh? It's a common misconception that since the label says 30 minutes one should have 30 minutes to get the pieces in place. In reality, the working time is less. The actual time is largely dependent on the temperature. When I'm doing a time critical thing such as gluing wing halves together, I always do a few trial runs before I mix the epoxy. If I think it will be impossible to get the whole job done before the epoxy starts hardening, I look for ways to divide the work into pieces. For example, on occasion I have glued the wing doubler to just one half of the wing, making careful to not let any epoxy ooze out. Once the first side hardened I then glued in the rest of the wing. Only if I am sure I can get it all done in one stage, and if I'm sure the wing doubler won't go in too far on one side, will I do the whole thing in one step.
    AMA 87959

  21. #21
    RCU Forum Manager/Admin RCKen's Avatar
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    I do the same thing that Piper_chuck does. When I have a task such as joining wing halves I will practice the actual steps I have to do to complete the procedure. I'll do it 2 or 3 times or until I can put everything together smoothly in the shortest amount of time. This way when I mix the epoxy there are usually no problems when I have the clock running.

    As I said before, I very rarely use 5 minute epoxy. I've had the same bottles of 5 minute epoxy for about 3 years now, that's how little of it I actually use. Any strength critical joints get 30 minute epoxy. A cheap substitue for microballons is corn starch (I have substitutes because the closed LHS is 45 minutes away, so I find things I have locally) and it works just as well as the micro ballons. On joints that need extra strength I will use a bit of fiberglass cloth on the joint with 30 minute epoxy on the cloth. I do have one use for thin CA that I haven't found a good substitute for, and it's really the only reason I still keep it around, and that's hardening the wood in screw holes.

    For the major part of my building I use Elmer's Carpenter's glue. I made the switch from CA to wood glue about 3 years ago and it's the best thing I have done in regards to building. Aside from the health issues I feel that the quality of my builds has improved since I started using wood glue. I have more time to make sure parts are properly set before the glue dries. And wood glue is a lot easier to sand than CA (which is impossible to sand by the way). I also don't glue my fingers to anything anymore. And my lungs love it that I don't use CA anymore.

    Thats my 2Β’ worth

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  22. #22
    piper_chuck's Avatar
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Only 3 years? I can top that, my 15 minute is 18 years old! Yup, that's right, it's 18 years old and still works fine. The bottles are still 2/3 full. I just don't use it that often. Meanwhile, my 30 minute is only half full and I've only had it for about a year and a half.
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Ken I'm glad you mentioned the wood glue, Thats what I use mostly around on other stuff and am comfortable working with it. I wasn't sure it was correct to use in an airplane fuse. But what about the fuel and humidity? I say humidity cause I'm down here in the swamps practically in S. Florida , ha maybe steam would be a better discription[sm=drowning.gif]
    Yup; I\'m the guy the hobby shop warned you about...

  24. #24
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    I've never had a plane fail at a glue joint and the only time I use 30 min epoxy is to join the wings, other then that I use 5 min epoxy, and I beat the crap out of my planes. Take it for what it's worth. Also, wood glue's advantages can be disadvantages depending on what your working on. I tried wood glue for the first time on my Sig SE, and I did enjoy using it but I still like my CA.

    I have found from this website that glue and covering can be like a religion for many people.
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    RE: 5 minute epoxy vs. 30 minute epoxy?

    Chuck do you use this Milled fiberglass? I saw it at Tower Hobbies and wondered about it, if anybody used it to build up joints. Once I start practicing on the balsa scraps I'll get more familiar.
    Yup; I\'m the guy the hobby shop warned you about...


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