Epoxy, TiteBond, or CA?

With no desire to start a religious war, my question is directed towards when it is appropriate to use one over the other? Where is the line between Titebond and Epoxy for the MM, Fins and Friends? I'm pretty sure I've seen folks use wood glue instead of epoxy for kits that are expected to have some high-powered motors. For myself, I'm guilty of replacing wood glue w/thick CA in low power estes kits (my 2nd mongoose) in the MM area and thick ca for a low power rocket bulkhead for the payload section in the LOC Hyperloc - mini missile version.

Are there any 'guidlines'? The most I've been able to infer so far is that if your rocket is going to be exposed to HPR conditions - use Epoxy. Else titebond will work fine . . .

Is there a considerable strength difference between the two?

Also, about titebond . . . does it matter titebond 2 or 3?

I suppose I could just follow the instructions . . .haha! But I am curious about how the decision is made . . .

Mark

Wood glue bond is stronger than either material being bonded ( wood, cardboard). As for the difference between TBII AND TBIII, Titebond 3 has a slightly lower tensile strength than TBII but TBIII is "waterproof" or at least highly water resistant.
When bonding 2 dissimilar materials ( plastic to cardboard or wood) then its time to start considering epoxy. For most plastic to plastic bonds there are a few different plastic adhesives that can be used.

rharshberger said:

Wood glue bond is stronger than either material being bonded ( wood, cardboard). As for the difference between TBII AND TBIII, Titebond 3 has a slightly lower tensile strength than TBII but TBIII is "waterproof" or at least highly water resistant.
When bonding 2 dissimilar materials ( plastic to cardboard or wood) then its time to start considering epoxy. For most plastic to plastic bonds there are a few different plastic adhesives that can be used.

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If materials strength were the primary reason for choosing a glude, then Titebond 2 would be sufficient in all cases where plywood and cardboard were used - correct? Epoxy does appear to make 'better' fin fillets, is there a way to improve TB2 filets sot that it can create same area/look as epoxy? Why is epoxy used? Is it really necessary? Sorry for the silly questions . . . (I'm good at those!). If I had my druthers, I'd rather work with Titebond than epoxy . . . but there does seem to be consensus that Epoxy is good for HPR, Titebond/Wood Glue good for LPR/MPR . . . If not, then?

Thanks for your patience . . .

Mark

Forget about HPR=epoxy.

If it's cardboard and plywood, TBII is stronger than the tube or the wood.

For easier fillets, try TB No-Run No-Drip ( formerly Quick-n-Thick or Molding & Trim )

dhbarr said:

Forget about HPR=epoxy.

If it's cardboard and plywood, TBII is stronger than the tube or the wood.

For easier fillets, try TB No-Run No-Drip ( formerly Quick-n-Thick or Molding & Trim )

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You can, of course, choose to use epoxy and it will do just fine. But it can weigh and/or cost more, and is less flexible.

I like 15min epoxy for CRs, MMTs, couplers because woodglue can 'grab' if you're not careful.

You can get the same fillet using wood glue as epoxy. You just use many thin layers of wood glue and build it up. The only benefit to epoxy when building a wood based rocket (paper, fiber, etc.) is time savings. You can use 5 min epoxy and have the joint cured in 5 minutes vs 20 to 30 minutes with wood glue.

I'm going to summarize what others have said without adding much new. Your welcome!

1) Yes, wood glue is satisfactory from a strength perspective for bonding between paper and/or wood. I generally use Titebond II. I don't think the extra water resistance of TBIII would generally matter.
2) As dhbarr says, wood glue has a tendency to "grab" rather suddenly in some situations. It can be a rude shock if your sliding in a motor mount and then half-way it stops. However, I find this only happens with rolled paper centering rings that fit tightly. I don't think I've had plywood centering rings grab on me. That said, I too have switched to epoxy for motor mounts for this. Note this applies only to gluing the mount into the body tube; I'll normally use TBII when gluing centering rings onto the motor mount tube. But even then you have to work quickly and decisively.
3) Doing beautiful epoxy-like fillets with wood glue, while possible, would be very tedious. As stated above, you'd need to do many layers, and all you get from it is cosmetics. I don't think it's worth the trouble. My fillet routine varies, but often I'll do one thin fillet with regular TBII just to make sure it flows totally into the joint, then I'll do one or two layers of TB Quick-and-Thick, and then done.
4) Wood -> plastic or paper -> plastic: epoxy works, but also some (e.g. @hcmbanjo) have had very good luck with Beacon Fabri-Tac glue. I haven't tried it myself, but will likely do so next time I need to do one of those joints in a model.

If you're going to use Titebond Quick and Thick for fillets (I do recommend it), I wrote a little tutorial about how to get good results with it.

"Plastic" is a general term, and from personal experience, most epoxies won't stick to most plastics. CA for plastic to ..
Some epoxies don't stick too well to fiberglass either..

CA, for me is brittle, hard to sand, and dries / cures in a mili-second. (and it'll glue your fingers together faster than the parts you're trying to glue!)

Wood glue is water based, and when it cures, the water evaporates. So, for doing fillets, you'll put down a nice bead, only to come back and see it's all pitted & such. That's why. The water has evaporated. Epoxy just hardens up (and gives off heat as it cures.. CA too..)

My Goblin when together with yellow wood glue. Epoxy & filler for the fillets.

dr wogz said:

Wood glue is water based, and when it cures, the water evaporates. So, for doing fillets, you'll put down a nice bead, only to come back and see it's all pitted & such. That's why.

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Quick and Thick doesn't generally pit, which is why it's good for fillets. It does however shrink plenty as it dries, so the fillet ends up a lot smaller than you thought it would be. Ability to do all your fillets at once, though, is very nice.

neil_w said:

Quick and Thick doesn't generally pit, which is why it's good for fillets. It does however shrink plenty as it dries, so the fillet ends up a lot smaller than you thought it would be. Ability to do all your fillets at once, though, is very nice.

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When it comes to fillets, I've been assuming - perhaps incorrectly - contact area is primary, looks and aerodynamics is secondary. If there is considerable shrinkage, wouldn't this reduce the adhesives contact area, forcing a second or additional application(s)?

Mark

No, the contact area stays, but the bulk is reduced.

neil_w said:

No, the contact area stays, but the bulk is reduced.

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Cool - thanks!

Mark

Does anyone use thick CA in structurally significant areas on MPR/HPR rockets? I used it almost exclusively on the 2nd Estes Mongoose (1st one disappeared, kidnapped by some cloud deity). It would appear that the only issue with CA is how brittle it is? Would using thick CA, just for arguments sake, be a 'good' idea or acceptable on a mid or high power rocket?
Thanks Again!

Mark

I build LPR. For any wood based component joining (balsa, plywood, paper body tubes and transitions, etc.) I prefer Gorilla Wood Glue for the first application. It's thinner and has a tendency to enter into tight nooks and crannies. The thicker glues tend to bridge gaps, and not penetrate them. That means a weaker joint.

So one or two applications of Gorilla glue to ensure the joint is filled, then Tightbond Quick&Thick for "pretty" fillets. Even with the Quick&Thick I do multiple thin layers. That helps to minimize shrinking. Probably a throw back to my welding days... multiple small welds are better than one big weld due to the stresses induced by shrinkage.

Patience is the key... it's more about the journey than the destination.

Photo's below show Gorilla Wood Glue, second application.

markfsanderson said:

It would appear that the only issue with CA is how brittle it is? Would using thick CA, just for arguments sake, be a 'good' idea or acceptable on a mid or high power rocket?

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Well, brittleness is pretty important. I think you will generally hear that CA is not appropriate for structural bonds for that reason. Many folks do use regular CA to tack down fins to hold them while applying epoxy fillets that do the real work. In this case it is not a structural bond.

As a counterpoint, when I was building my Accur8 Ragnarok Orbital Interceptor, I corresponded with John Pursley and he described how he used a CA double-joint method with great success. That is, apply a coating of thin or medium CA to each surface, and then bond them with more CA. That is a very non-traditional approach, and I did not have the nerve to try it. It is worth noting though that John Pursley has likely forgotten more about rockets than I will ever know.

Personally I would be disinclined to use CA as a structural glue in MPR or HPR applications.

another item (or two) to consider before choosing an adhesive, is how well the joint fits? ca and wood glue are not at their best at gap filling, while epoxy is better. shrinkage, wood glue shrinks as it cures/dries...if you're not careful you'll be able to see where every centering ring is located simply by looking at the outside of the tube (it is called the 'coke bottle effect').
Rex

I think it's worth repeating that the best wood glue joints are achieved with no gaps and pressure applied during curing. This becomes more important as you move into L1 and L2 construction. The coke bottle effect can be mitigated by using a thin layer of glue at the centering ring attachment points. I just use a non-shrinking glue for motor mounts, Gorilla polyurethane. My 2 cents

The only rocket that I used CA for all contruction was the mpr Aerotech Barracuda. As specified in the instructions. No problems after years of regular flying.

samb said:

The only rocket that I used CA for all contruction was the mpr Aerotech Barracuda. As specified in the instructions. No problems after years of regular flying.

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Same for my Mustang, gel CA. Worked great until I overdrilled a delay, fins were still locked solid even after the burnout.

markfsanderson said:

Does anyone use thick CA in structurally significant areas on MPR/HPR rockets? I used it almost exclusively on the 2nd Estes Mongoose (1st one disappeared, kidnapped by some cloud deity). It would appear that the only issue with CA is how brittle it is? Would using thick CA, just for arguments sake, be a 'good' idea or acceptable on a mid or high power rocket?
Thanks Again!

Mark

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Yes, but I had to do some joinery. A Mean Machine upscaled by kit bashing two Mammoths. I put it together the night before driving out to the desert for a launch. The only glues I used were gap-filling/slow cure CA and toughened CA. Through-wall fins transmit thrust from the rear centering ring to the airframe. I also cut dados in the centering rings to receive the fin tabs. There isn't really any place where the glue joints are under shear stress.

I am going to send it up on an H this season. We'll see how it holds together.



My 2¢: I sometimes use epoxy because I live in a wet climate, and I don't have the patience to wait for wood glue to dry. I also, sometimes, use polyurethane glues when I am doing key-hole surgery -- trying to get the glue into a space too tight for my big clumsy fingers to reach.

edit: It occurs to me that the fact that the rocket was designed to keep stress away from the glue joints might mean it wasn't used in "structurally significant areas" -- so I revise my comment from a "yes" to a "maybe".

Generally:

CA: Plastic-plastic, plastic-whatever, mostly LPR/some MPR. Sets really fast. Sometimes that's good, sometimes that's bad.
Wood glue: Cardboard-cardboard, cardboard-wood, wood-wood. Some LPR, some MPR, some HPR. Kind of slow-setting for me and I kind of dislike the shrinkage.
Epoxy: Quantum tube, fiberglass, carbon fiber in some MPR/mostly HPR. Works fine on cardboard-wood as well. Set time depends on the particular product.

Personally for the last two years I've used nothing but Gorilla 5-minute epoxy on everything from 54mm (non-MD) cardboard-wood MPRs on F motors to 4" fiberglass/QT/canvas and 8" cardboard/wood HPRS on J-K motors and have yet to have a problem with adhesive failure.

Gorilla 5-minute epoxy is cheap, readily-available, flows well for doing fillets, and sets in a few minutes preventing the need for elaborate jigging. I like the ability to spend a few minutes getting it where I want it, and then having it set relatively quickly. I suspect it may be a little more brittle than longer-setting epoxies, but I have yet to snap a joint. It's really my go-to adhesive until/unless I find a reason to use something else.

I think another thing that has to be said, is that many may not know:

• how gluing / bonding works.
• if there is a difference between gluing, bonding, and cementing.
• what glues work for a given material / purpose.

Most will grab what worked last time, not realizing that there may be a better glue or method to joining parts. And that some glues don't stick at all, but hold the piece due to the build-up around the piece; encapsulating it.

dr wogz said:

if there is a difference between gluing, bonding, and cementing.

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OK, I'll bite. Care to elaborate? My initial Googling did not yield clarity.

neil_w said:

OK, I'll bite. Care to elaborate? My initial Googling did not yield clarity.

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Frankly, my initial search didn't reveal much either.

I remember in school we were told there is a difference between bonding and gluing..

• Gluing relied on a film, and extra "substance" between the parts being attached. Glue, Epoxy, etc..
• Cementing relied on similar material in an altered state to join the parts, such as using acetone to melt, then join / weld ABS plastic together..
• I believe bonding was like gluing, but relied on another process to set the adhesive, such as heat or UV

I do plan to add some elaboration, but my lunch hour is only so long!

neil_w said:

OK, I'll bite. Care to elaborate? My initial Googling did not yield clarity.

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Try "glue+adsorption", "glue+chemisorption" and "solvent+adhesive". There are also adhesives that diffuse into porous materials and harden, so that the bond is partly adsorption and partly mechanical (facilitated by the cohesion of the solidified adhesive)

Ok, looked that stuff up, interesting but no big surprises. I did not come across anything that specifically correlates adhesive types with the names "gluing", "bonding", and "cementing" however.

That's the point I wanted to make, that regardless of the "glue", they can and do work / act differently. For example, Model cement is great on plastic (ABS) because it partly melts the parts being 'bonded'.. But it don't work on balsa or ceramic tiles.. Whereas Epoxy does, because it seeps into the nooks & crannies of the irregular & [somewhat] porous surfaces of wood & paper. (and why epoxy is crap on plastic because of the missing nooks & crannies, except for a really roughed up surface..)

neil_w said:

Ok, looked that stuff up, interesting but no big surprises. I did not come across anything that specifically correlates adhesive types with the names "gluing", "bonding", and "cementing" however.

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I was guessing that "cement" was going to map to a mechanical joint secured in a matrix of hardened stuff and that "bond" was going to mean some kind of chemical modification of the adhered surfaces. But yeah, not so much.

Thanks for everyones input! That's the great thing about this forum, tons of experience and perspectives . . . everyones been very helpful!

Mark