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Old Feb 16, 2012, 09:12 AM
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How much hot glue? (and why not Gorilla Glue?)

Hi everyone,

It's a bit late for me to be asking this question, as the major assembly of my Mikey's RC FPV V3 is complete. In accordance with his suggestion, I've used hot glue for most of the plane. I've got mixed feelings. Sure, it's fast. And seems to be very strong. However, I started counting how many sticks of hot glue I put into this plane and I'm disturbed by the weight! So my questions:

1.) Maybe I was using the right glue, but in the wrong (i.e. excessive) amount? Maybe instead of gluing the entire joint, I could just apply spots or strips. Or maybe I need to apply a much thinner bead. On some joints, I did this: Apply UHU Por to the faces of the joint, allow it to try. Stick them together, then add hot glue in the corner, sort of like caulk. Maybe I could have used a really thin corner bead?

2.) Maybe hot glue's virtues (that it's fast) could be enhanced by just using it as a quick hold, while a more lightweight glue (i.e. Gorilla Glue) has time to set? In other words, apply Gorilla glue to the two surfaces to be joined, then immediately lock the two surfaces into place so that they dont seperate as the Gorilla Glue does it's foamy thing.

Any thoughts?
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Old Feb 16, 2012, 01:05 PM
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I preface this by saying that I'm not an expert on (A) building models, (B) glue and epoxy chemistries, and (C) woodworking, although I have experience with all three.

Gorilla Glue was formulated for bonding highly resinous woods like Teak, that have so much oil and resin in them and are very dense, so standard PVA glues (typical wood glues like Elmers and Tightbond) don't work well on them. For that purpose it seems to work, although there seems to be general agreement in the community that there are better products for that specific application.

Gorilla Glue has been heavily marketed as being a universal do-it-all glue. While it is true that it binds nearly anything to nearly anything else, it is also true that in pretty much every case there is a better adhesive to use than GG.

I have a number of problems with GG. First, it is messy and a pain to work with. The foaming is difficult enough to deal with on woodworking projects that I can clamp in a vise to clean up. I don't want to think what I'd do with GG on a balsa airframe. Secondly, it doesn't store well, so you waste most of whatever you buy. It is a very poor value. Third, the chemicals released during curing are carcinogenic so you should wear a respirator when using it. Like anything else, take precautions as you see fit.

I like hot glue on airplanes and I agree that you may be using too much of it. I see no reason to melt a line of glue along an entire joint. A few spots here and there will provide holding power, remain flexible, and be easily repaired.
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Old Feb 16, 2012, 06:40 PM
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Hi Andy,

Wow--had no idea about the carcinogenic fumes. I would imagine they are pretty low doses on an average build, but that's good to know anyway. Guess I'll open a window next time!

I definitely agree about the messy factor! I guess I just like how light it is.

I suppose my next question is: How do I know how much hot glue to use??
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Old Feb 16, 2012, 06:41 PM
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- hot glue is weak (tho most medium->high temp guns will melt into the foam & foam a good bond on foam)
- hot glue is crazy heavy
- hot glue looses strength & turns brittle over time (tho the typical throw away foamy do not have the lifespan to encounter this problem)
- beware of low temperature hot glue, they dont melt into the foam well they're meant for little kiddies
+ hot glue sticks store pretty much indefinitely
+ hot glue is available EVERYWHERE
+ hot glue is cheap as sin

well say gorilla glue, but this is indicative of all polyurethane glues
- gorilla glue is expensive
- gorilla glue has a short shelf life
- gorilla glue is a hot mess, impossible to clean up unless you do it IMMEDIATELY with denatured alcohol or acetone
- gorilla glue foams everywhere
- gorilla glue has a long set time (several hours)
- gorilla glue must be clamped
- gorilla glue has a low shear strength (the glue ITSELF is stronger than most foam. unfortunately it's low shear strength can allow the joint to peel off decent foam like depron/epp)
- gorilla glue can't be finished on wood. it wont sand, it wont paint
+/- gorilla glue is not really better or worse than anything else in regards to temperature (it will freeze & become brittle, it is quickly softened with head)

+ gorilla glue will foam & fill gaps
+ gorilla glue hasn't been found to react negatively with foam & plastics






gorilla glue is popular, but it's waned a lot since release. the only two hobbies i can think of it has a strong hold is foamies and pottery.
i quit using it. its hard to use a full bottle up before its just thick & goes bad. Epoxy, hotglue, PVA (glue-all if you want clear & 12 hour set times, titebond if you want waterproof & sub hour set times) work fine for me on foam. the super best use of hot glue that i've found. is that its useful to tack pieces together if you're not a CA user. elmer's glue-all takes relatively foooooor eeeevvvaaaaaaar to set if you dont speed it with heat. so a couple little hot glue tacks make it better.


hot glue... it just takes the place of CA for people that dont use CA for whatever reason. (cost, shelf life, allergy dangers, w/e). its just heavy as sin & not as strong outside of heavily melted foam joints.
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Old Feb 18, 2012, 08:11 AM
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Fantastic reply....thanks for the details. Guess there isn't a single-glue solution!

I've never tried PVA. Any idea of other names for it? Or what PVA stands for? I'm buying in Asia and the brands are usually not the same.
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Old Feb 19, 2012, 02:11 AM
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PVA stands for Polyvinyl Acetate. You've almost certainly used PVA glue if you've ever used a white or yellow carpenter's glue craft glue.
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Old Feb 19, 2012, 02:30 AM
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Ah! Elmer's glue = PVA? The things you learn in this hobby...

Is Latex glue also PVA?

I'm starting to think that I can use hot glue exclusively, but just much more sparingly. For example, along the fuselage/wing joint, I can probably make half inch beads seperated by 1" of no-glue. It's probably more than strong enough with that amount. Guess there's only one way to find out...!!
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Old Feb 19, 2012, 11:35 AM
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Hot glue is fantastic stuff; for making jewelry, book ends, and boat balast. For aircraft, there are way too many other, lighter, stronger, more appropriate adhesives/glues.

Les
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Old Feb 19, 2012, 12:52 PM
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You *can* control the GG foaming as it's curing somewhat, but it is still a pain. Like most stuff in this hobby, once you get the hang of it, it is very useful in certain situations. I agree about the shelf life and waste, though. I probably won't buy any more after my current bottle. Toysrme has it with the "melting into the foam" deal. Most folks use the tip like a welding tip melting the foam a bit and using very little glue. Gotta be careful in places where it shows, but that's the way to go with hot glue.
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Old Feb 19, 2012, 05:49 PM
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I can see SOME places for hot glue in model airplanes. But I've yet to have to resort to using such stuff in any model I've built or repaired. It does not lend itself to precision building since the glue lines are relatively thick. And if pressed out thin the film is so thin that it cools too fast and does not get as good a deep bond as with other styles of glue.

Using it as an external "bead" adds lots of weight and very little, if any, strength.

So all in all it's a very poor choice for most styles of model aircraft building.
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Old Feb 19, 2012, 06:58 PM
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Hmmmm.....all good pieces of information.

What glue would you recommend for joining EPP wing halves? I'm patient....
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Old Feb 19, 2012, 07:07 PM
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Now the bigger question: What to do with a model that I've used hot glue in the worst way (i.e. heavy external bead) on!? Probably not way to remove it without destroying the model....sigh....

Toysrme and Johnspop: I'd love to see a picture/video of what you mean by using the tip to melt into the foam.
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Old Feb 19, 2012, 07:29 PM
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Quote:
Originally Posted by BMatthews View Post
.....................

So all in all it's a very poor choice for most styles of model aircraft building.
I agree. However, it does seem to be good for coreflute planes, which are quick and expendable.
I use it a lot for setting up bench jigs for decalage alignment, vacuum bagging (secure the beds to the bench), and too many reasons to list. Also for securing wiring looms in aircraft fuselages and such. I also use for final fixing of servos after I have cast an epoxy/"'Q" cells pocket for the servo. Two or three small spots of hot glue will secure it. If it requires removal, a heated wire will soften the glue allowing removal.

Jim.
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Old Feb 20, 2012, 02:15 AM
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Originally Posted by doughpat View Post
Hmmmm.....all good pieces of information.

What glue would you recommend for joining EPP wing halves? I'm patient....
Oddly enough from the little I've used EPP for anything hot melt glue may not be a bad option at all. The foam of this nature I've used for other uses has been very "pourous" what with the cell structure. It takes a fairly gap filling glue to join such material. And a hot melt glue works very well in this particular case. So you sort of tripped up the whole "better adhesive options" direction of this thread by mentioning "packing foam" for building models...

It still doesn't dismiss the concept of PROPER use of the hot glue in order to get the most utility out of the least amount of glue by using it properley instead of gobbing it on with external beads.

For example take your wing joining question. A good way to do a wing joint of this sort is to run a bead around the outer edge of the joining faces and then push the halves together. That way only the outer edges are glued. In the middle they are not. This supplies a 95% solution for strength with only about 50% of the glue that would have been used if the whole face was buttered up with the stuff.
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Old Feb 20, 2012, 07:01 AM
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Hi Bruce-

Thanks for the tips. I'm going to try this for the wing halves: "butter up" the inside of the face (minus the ~1/8" margin) with gorilla glue, then apply hot glue in about 1/2" segments, leaving a 1" gap in between each segment of glue. I'll press them together, hold until the glue cools down, and then I'll use some masking tape and run it around the joint to control the foaming of the gorilla glue. Hopefully this will get me 90% of the strength with 25% of the weight

We'll see how it goes...
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