Epoxy v. CA
 

I have a question about the difference between epoxy and CA glue. Why do plans sometimes call for epoxy and sometimes call for CA? What's the difference (other than consistency and method of application)? Do they have different binding properties, and are there situations when one should be used and the other one should not (aside from the obvious situations like CA hinges and not using thin CA when you need some time to manipulate the parts)? Or are they pretty much interchangeable? Is one stronger than the other and thus, more desireable for a certain application? For example, my SIG four * 40 kit calls for thick CA to install the wing joiner, but my Avistar Trainer called for 30 min epoxy to install the wing joiner. What gives?

RE: Epoxy v. CA
 

Epoxy is stronger and I would use it in most cases for joining wings, putting on tail surfaces and firewalls and gear blocks, wing blocks for the wing screws to go into, stuff like that. You can get by with CA on some of those applications, but I would be a lot more comfortable with epoxy in those. The rest pretty much use CA. I have built entire planes with CA, but on power birds, I just like the strenth of epoxy in places like I explained.

RE: Epoxy v. CA
 

Epoxy is beter when there is a gap to fill.
Epoxy is better for when you need time to position parts.

CA is better for speed of assembly. (and that is about the only place its better than some other glue in the same place... except installing CA hinges.)

Yellow glue can replace CA in 90% of cnstruction and resutls in an easier to sand, lighter structure. (and costs a LOT less) You end up spending enough more time sanding with CA that... the yellow glue is quicker in the long run.

Almost always, the glue is stronger than the wood... so strength isn't really a big factor in choice of glue. If the wood breaks first... the glue worked.

RE: Epoxy v. CA
 

Try all the glue types. You'll find out what you like. Epoxy rules for high strength bonds but is messy. Wood glue is nice but not as strong in my opinion. Cleans up easily and sands. You can do things with thin CA like put some baking soda on your joint that will make it like concrete but it sets instantly and creates fumes. I used Thin CA, Med CA, Tightbond II, Epoxy and will try Gorilla glue for the Robart hinge points on my last plane. I like having every glue ready to use as different situations call for different glue.

RE: Epoxy v. CA
 

Thanks for the tips. Maybe I'll do some strenth tests on some scraps of balsa and ply. My guess is that I'll find that both types of glue are much stronger than the wood. That's a good point about the ability to sand the glued joint down. I'm running into that very problem right now. The balsa sheet on the last bay on the left side of my four * 40 wing got crunched when someone knocked something over onto it (not me). I lined up all the sheeting and then wicked thin CA through the spot. Now it's hard as a rock and there's no way I will be able to sand it down before I cover it. And the wing is now unbalanced too. I'm debating whether to just cut off the last bay as many have done with their four * 40's or whether I should cut out the offending piece of sheeting and replace it. Any suggestions?

RE: Epoxy v. CA
 

Don't worry about the extra weight on the left tip....you will need it to offset the muffler on the right side of the fuselage. If you can't sand it down well enough to cover over it without lumps, just replace the sheeting.

Clair

RE: Epoxy v. CA
 

I find that normal (white) wood glue is about as strong as you'll need in building model aircraft. I've used white glue for years in numerous applications, and found it really satisfactory. My observation is that a wood joined with white glue, if prised apart with a chisel, will split the wood, whereas a joint with epoxy will usually pull the glue itself apart, and that tells me that the white glue makes a stronger joint.

There is another glue that I think is better than all others, and that's Fuller's Max Bond. It's thick and difficult to use on small applications though, more a construction industry glue, but for bulkheads to fuselage, it can be used successfully. Liquid Nails is similar.

The advantage I find with white glue in modeling is that when it comes time to repair, and there will be such a time, the cleanup and repair will be easier than if epoxy was used. It can be cleaned off and sanded easily, and a new joint made much more easily than the epoxy joint.

However if there is even a slight possibility of a gap, then white glue is not suitable. It doesn't gap fill.

RE: Epoxy v. CA
 

You may find this crazy and completely unecessary, which it was. But, a buddy of mine many years did an experiment with a Skybolt. Believe this or not, he built the whole plane using only 1-hour EPOXY. It sounds crazy, but it actually worked really well. HE would mix small amounts and use little drops on everything, even for the framework. When he was done, that plane didn't weigh anymore than he expected and was well within the weigh specs of the design.

One day he came in for a landing, caught a sidewind (yeah right), lost it and cartwheeled most beautifully down the grass runway about 4 times over. Looked just like Mary Lou Retton, YEEHAWWW!!!!!

Amazingly, that little plane came out with just a few dings. He had it flying in a couple days after fixing the covering and filling a few dings. Granted, it is a pretty beefy little plane to begin with, but this little epoxied version was about the toughest little bipe I have ever seen.

Now, I am not saying in any way that we should build our planes with nothing but epoxy. But I thought it would make a good story.;)

Patriot

RE: Epoxy v. CA
 

No need to bother with the strength tests... they have been done.

Epoxy, CA. Polyurethane and Yellow glues all are stronger than hard maple when applied correctly. The wood will break before the glue lets go. That includes being stronger than Aircraft ply which shears before a proper glue joint.

But there is also the problem... getting a proper joint. CA is very hard to get a good joint more than 1/4 inch from the application point, and CA dries so fast, you can't do a good lamination with it.

CA is useless for filling any gaps... and that includes the gap filing formulas.

Epoxy excels at filling gaps, but adds lots of weight while doing it.

Yellow glue is OK for some gaps and is the one of the best glues for doing wood lamination work. (the only better glues for wood lamination are hot application specialty glues used at plywood factories... You'd have a hard time getting any.)

Polyurethane glues can make a porous bond, and are the most likely to fail before the wood if there is any problem with the application.

RE: Epoxy v. CA
 

My $.02 -

Agree that the joint must be tight for any adhesive to work well... I use the following

Aliphatic resin (waterproof when dried) when I neet time to adjust the joint - cheap and light, good penetration, sands well, excess can be removed with water when it is still liquid - overall my first choice for strong joints - takes a while to dry, but there are LOTS of other parts on an airplane to work on :D

CA when I am assembling wing ribs and spars - quick and easy to use - bonds tight balsa joints very well... I use CA accelerator very sparingly

Epoxy when joining different materials - metal to wood, plywood to balsa or hardwood to plywood - messy; thin or clean up with denatured alcohol

Gorilla glue - have heard great things, and have a bottle ready to try -

HTH

Jim

RE: Epoxy v. CA
 

Wow! Great information folks. This is very educational. Glad I asked.

RE: Epoxy v. CA
 

Another thing to keep in mind is that many glues won't bond plastic to wood well such as when gluing in control rods. I have been using epoxy for this. CA doesn't work well at all. I'm not sure about the other glues.

RE: Epoxy v. CA
 

One more thing to add to what has been already said above is epoxy, especially the slower cure ones, needs clamping. CA does not

RE: Epoxy v. CA
 

as to your original question are there some applications where one should be used over the other (epoxy vs ca) the answer is yes most definatly. CA dries brittle this is fine for joining ribs to spars, sheeting, and really most all frame work, but, and this is important here, places like firewalls, motor mount rails on kits that use them you really really should use epoxy because it is more flexible, now dont picture silly putty here, but it can handle vibrations from the engine much better without the worry of the joint cracking. as for using ca for wing joints i guess you can using med or thick CA for the cure time it allows more time for the glue to soak in and thus a better joint but i always use epoxy and C clamps. its like this nails vs rivets sure theyre both fasteners but you wouldnt build a jet with nails and you wouldnt build a house with rivets although i guess you could bottom line is use epoxy where it is needed and yes you can even use it where you could get by with CA as was stated in the all epoxy plane but using CA through out would be a mistake

RE: Epoxy v. CA
 

Jimmbbo said it all....except some people like me are allergic to CA glues. I get the odorless type for wing ribs, etc. But it's expensive. I've tried building without CA, but the builds always result in blobs of glue to be removed. It chips off or sands more easily than CA, but it's another step.

RE: Epoxy v. CA
 

try yellow glue... no harmful fumes... and you wipe up the drips with a damp rag... so youdon't have to sand or chip them off later.