Just curious what some opinions are on the difference in bond strength between 15 and 30 minute epoxy when using either one for a wing joint. I know the working time on the 15 minute is shorter, but what about bond strength? Are they fairly equal, or does the 30 minute have a significant advantage?

I think the 30 minute provides a stronger bond. I use that on all wing joiners and any place where I need strength.

Dave...

Hi. To keep this simple the longer the "labeled' work time the stonger the bond once "full cure" is achieved.Think about it like this ,the longer your epoxy stays "wet"the more time the epoxy "sinks"(capillary action)into the grain of the wood.A quality bond won`t break in an accident,but the wood around the "joint" does.
FLY for NOW!!!!!!! DAVE B.

I don't even use epoxy if I can possibly avoid it. The stuff is heavy, messy and too expensive to be worth the hassle. I keep some 5-minute around for quick get-back-in-the-air field repairs, and I'll use 30-minute for glassing center sections, but I'll use polyurethane for gluing wing center joints, firewalls, gear blocks, etc. Light & cheap. And, when you're breaking the wood before the glue gives, what the *&^% difference does the composition of the bonding agent make anyway?

The slower cure times are stronger, not because of the soaking into the wood but because of the polymer chains formed during cure are much longer. Just remember, all epoxies (even 5 minute) does not reach full strength for 24 hours. Also, epoxy is no heavier than any other glue if properly applied. Don't use it as a filler for bad joints, make good joints and use only enough to wet the surface to be joined.

You can get 45 min epoxy as well. Followng the theory that the longer the working time, the stronger the bond.....45 should be better.

On my plane, I used aliphatic glue for the actual joint (wouldn't do this again, though), then wrapped 4" fiberglass tape around the circumference of the joint. I had epoxy under and on the top of the tape. Use an old credit card to smooth it out. Can even put saran wrap over it and smooth with fingers.

I think this will make a strong joint. Be careful, however, because too wide of tape will cause the wing not to be mounted correctly.

THE POINT IS IF YOU ARE GOING TO BOND SOMETHING, IT MIGHT AS WELL BE GOOD!!. IF IT DON`T MATTER.USE SCOTCH TAPE IT`S EVEN QUICKER THAN 5 MIN EPOXY.NO MIXING AND IT`S A SINGLE COMPONENT, READY TO USE.IT`LL TAKE UP LESS SPACE IN YOUR FLIGHT BOX TOO .D.B.

Hi!
You are right SST!
Who cares what you use to bond together two winghalves when all glue available to us hobbyists is stronger than the wood we use (balsa , plywood and foam).
After 30 years in this hobby I prefere "Flash" Ca glue for most of my building and of course accelerator.
I never use a single heavy glassfiber peice on my wings, instead I use 25g weave put on in several layers, cut into a diamond shape with 4-5 layers, doing one side of the wing at a time.
And I do recommend not to use anything other than polyester resin or 24 hour epoxy for reinforsing the wing center. These materials are very easy to sand and wet the glassfiber much better than ordinary "glue" epoxy.
Regards!
Jan K
Sweden

Most likely the cost of the materials you use in the above described method (polyurethane glue and then 30 minute epoxy to glass the center) is more than those of us who just use 30 minute epoxy on the ribs and joiner. It probably ends up weighing more too. The amount of time you spend is definitely longer. And it's hard to understand how it's less messy than gluing the center and cleaning the excess with alcohol before it cures. But, if it works for you, enjoy.

Z-poxy wets out glas as fast or faster than anything I`ve seen before
DAVE B.

Don't know about the strength of the actual epoxy, but the whole joint will be stronger with the slower-setting stuff. I almost never use epoxy. As another poster mentioned, it's messy, heavy, and hard to work with. As for the poster who said it isn't any heavier...use enough epoxy to make a good joint, then make the same joint with CA and weigh them. I'd NEVER use anything less than 30 minute (preferably 45 minute to 2 hour) for structural joints. It sets up too fast to soak into the wood enough to make a really strong bond. I've seen crash-damaged firewalls, repaired at the field with 5 minute epoxy, snap off with just a slight pull. Use 5 minute for non-porus materials and for fuel-proofing.

Dr.1

Jaka -- is that an Ultra Sport wing?

I use Probond where I can -- It's light, gap-filling & tough as a rock -- perfect for wing joints

I believe I was the poster who said it was no heavier, but my comment was not a comparison between epoxy and CA joints, it was a response to someone who said using polyurethane for the wing joint was lighter, but he said he then wraps the joint with fiberglass and epoxy.
Field repairs with epoxy usually fail because they don't have enough time to properly cure, but I agree with not using 5 minute epoxy.

Hi!
It's a 1/4 scale "Midget Mustang" wing (span 165cm). I bought some of these 1/4 scale pylonracers (Rivets, Midget Mustang, Little Toni, Shoestring etc) from a small company (Quay Baber Models) in Ohio 12 years ago, who specialized in making glass fiber 1/4 scale pylonracers. But the founder died and the company seized.

Regards!
Jan K
Sweden

would it be Ok to use the Z-poxy resin to glue on a foam balsa sheeted fin to the fuselage?
I know it will take about 3 hours to cure, maybe even 24 hours, but is there any disadvantage, as compared to 20 or 30 minute epoxy?

The main reason to use epoxy for high stress structural areas like wing saddles, firewalls, landing gear blocks, and wing mounts is the thickness of those joints. Any glue that requires exposure to air to harden isn't ever going to harden fully inside of a wing joint. With epoxy, you get 100% hardening throughout the joint assuming you mix it right. The second reason is the properties of the cured epoxy itself. Cured epoxy is basically a flexible plastic. It can be pulled on and vibrated without breaking. If you don't believe me, spread a dab of whichever glues you have available on pieces of wax paper and let them cure. Cured CA and poly glue will break like glass; no strength at all. Aliphatic will too. But the Epoxy will actually take some effort to break; some of them will just bend back and forth and not break at all. The other glues are great for their intended purposes and will make joints stronger than the surrounding wood. But epoxy is the perfect glue for these structural joints.

As for the original question, the biggest difference will be the soaking in. So 30 minute epoxy is the way to go for anything structural. I don't think there is any benefit to going with longer working time epoxies since properly mixed and applied 30 minute epoxy will make a joint so strong the surrounding wood will break before the joint pops loose in a crash anyway. And as stated above, 30 minutes is the working time, not the full cure time. It's the best policy to wait 24 hours before flying a plane after gluing it. Don't even work on it or move it around during that time if you can help it, because the joint is fairly fragile for those first few hours of curing.

I was able to do this with the Zpoxy resin, took about 3 hours, but I know, totally cured will be 2 to 3 days. This bird will not be flying anytime soon! Still have to build wings/hatch/canopy/cowl. then paint and cover.

Hi!
As I said 11 years ago I use Ca glue for most of my building.I never use 30min epoxy! Glue epoxy is messy and heavy and is very hard to sand.
The bonding strenght of All glues is so good that it's not the glue it self that breaks. What's important is how the wooden parts fit! In your case gluing the fin to a sport airplane ordinary thin or medium Ca could be used and of course accellerator, thats a must!

And if I followed that line of thinking, my boats wouldn't last a competition heat of racing. As said above, most adhesives are very rigid, making them brittle in high vibration areas. Epoxy is, on the other hand, flexible when cured. While much of an airplane CAN be built using CA, I wouldn't use it for landing gear blocks or firewalls. The ability of CA and most other adhesives to hold two pieces of wood together is only half the battle. If it can't take an impact or stand up to vibration, how much good is it really? A hard landing/jarring impact can and will break a glue bond while an epoxy bond will hold up to it. I wouldn't even put a boat on the water that's built without epoxy in all the joints. As for an aircraft, I'd rather sacrifice a few grams and be sure than skimp and watch the engine/fire wall spiral away from my plane. BTW, my boats only do 50+ across the water using 50%+ nitro fuel, they don't just putt around the pond

wow! You are serious, sounds like to me. No way I would ever glue a fin on a 40% airplane, weighs 46 pounds, with CA glue! The fin has foam under it as well. it is foam sheeted by balsa.

Only glue to use would be Titebond III, poly-urethane glue, or epoxy glue. MY question was whether epoxy resin is as good as 30 minute epoxy, I was never asking and would never consider, and do not know of anyone that would build a 40% aircraft with CA glue. Best regards
Cam

You can build a 40% with CA. I would use epoxy in any area that is high stress(i.e. wing mounts, landing gear blocks, firewall, stabs).
One thing I would like to clarify; epoxy is a two part adhesive. Resin is just one half and, by itself, won't bond anything. You have to mix it with a catalyst/hardener for it to actually set up. Some use a matched set of chemicals while others use one resin with an assortment of different hardeners.

I am confused. SO epoxy glue is not a two part adhesive also? I mean, what are you trying to say? both Resin and Epoxy glue (30 minute), there are two parts to them. one without the other, it will not adhere. What Am I missing here?

I have been using Epoxy glues since 1970's, and always, there are two parts to them. I am interested to hear what you are trying to say, otherwise, i am just not understanding what you are trying to say, and for that, forgive me.

You misunderstand. Hydro is just saying that Epoxy is indeed a two-part adhesive. One part is Resin and the other part is Hardener.

ok, I got you, he was just stating the obvious then. Thank you for that clarification.