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Old Feb 22, 2012, 05:12 PM
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Best glue for repairing planes (foam)?

Hi everyone,

What is the strongest/best glue that is foam safe?
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Old Feb 22, 2012, 05:22 PM
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Try Gorilla Glue - the honey colored stuff. It will expand as it cures, so it will have a tendency to bubble out of gaps etc. Just wipe off the excess before it cures. Dries white, but it does need to cure overnight for best results.
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Old Feb 22, 2012, 05:47 PM
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hot glue works really good on foam.
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Old Feb 22, 2012, 07:27 PM
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Hands down gorilla glue. Just make sure to wet both surfaces first because that is what creates the foaming reaction. I like to use packing tape to keep the glue from expanding out to far and it also helps keep the pieces together while the glue sets.
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Old Feb 22, 2012, 07:49 PM
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Exactly what kind of foam you are asking about?
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Old Feb 22, 2012, 07:52 PM
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Gorilla glue is OK but I recommend you do not wet both surfaces. Wet one (just damp not dripping). Put the glue on the mating surface. If you wet both surfaces the glue may start to cure before you get the pieces in alignment.

Glen
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Old Feb 22, 2012, 08:22 PM
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+1 for Gorilla Glue White. It dries twice as fast as the brown stuff and it cures as a white foam, sandable, light and blends will with your airplane.

Gorilla glue is much better for foam than hot glue, epoxy or CA because they all introduce a hard dam across the foam. Forces on the plane are no longer distributed throughout the entire wing, for instance, but concentrated at the glue joints because they are a sharply dissimilar material. This will cause a failure at or adjacent to the glue line.

With Gorilla glue, the joint is just more foam. If it's a wing, it can still flex evenly along its entire length with no concentration of forces along the glue line. You've restored the original resiliency of the component.

The Gorilla Glue joint will also be lighter, both in color and in weight.

I just have one question. Does ANYTHING dissolve the Gorilla Glue that gets on your hands? Wear gloves.
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Old Feb 22, 2012, 08:28 PM
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depends on the break, time needed for repair, and type/thickness of foam. For instant (almost instant) repairs on clean breaks in thin foam... Foam safe ca and kicker (accelerator) Breaks that are not clean... thicker foam... can wait overnight... with chunks of foam missing... Gorilla or hot glue to fill voids. Hot glue being the faster, but maybe not the preferred (IMO) You got to watch hot glue guns... there are a few different temps out there... some "hot" glues can melt/deform your foam. (especially if thin foam) There are also many different types of hot glue sticks. Make sure not to pick up some for woodworking. Wear disposable gloves when working with gorilla glue if your like me. I wore it on my hands for a few days. when you try to wash if off, the water activates the glue.
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Old Feb 22, 2012, 08:37 PM
oic
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sounds like you've been there done that Rockin Robbins...lol. Gorilla is my favorite on my larger foam planes.
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Old Feb 22, 2012, 08:51 PM
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white GG, try cleanup with paint thinner as per instructions on the bottle.
haven't tried it yet, but should work.
white GG seems to work very well on foam....I've had no failures yet
i use thin coat on one surface to control foaming....tape works great also, i use the blue, paint trim tape
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Old Feb 22, 2012, 09:58 PM
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Quote:
Originally Posted by RPTheLefty View Post
Hi everyone,

What is the strongest/best glue that is foam safe?
epoxy without question is the strongest. most epoxies also tend to be heavy if not thinned with denatured alcohol. they will bridge gaps & can be used as a protective coating.
epoxy has both a high shear strength and high tensile strength will bridge large gaps, is cheap & available anywhere
PU glues (gorila) have a relatively high tensile strength, but a very low shear strength. PU will literally peel off the foam (instead of ripping out foam). hard to clean up (requires denatured alcohol or acetone solvents), low shelf life & expensive & does not finish well (painting or sanding)
PVA's are strong and a little elastic, are BY FAR the lightest common build glue. (every other glue type absorbs moisture to cure. PVA is mostly water and evaporates it to cure) clean up easily (water), finish easily (sanding, painting) & are very cheap & available anywhere
CA's are strong, rigid very quick drying, low shelf lives & expensive. you can become violently allergic to CA fumes.
Hot glue can range from "just strong enough" when melted into foam (high temp) to exceedingly week (low temp). high temp tends to be somewhat elastic. they are cheap, readily avalible, but without question is the heaviest of all commonly used hobby glues. due mostly because it is not applied as a NORMAL glue. NORMAL glues, the TIGHTEST joint and least glue possible will yied the HIGHEST strength. Hot glue has mediocre strength & wont spread thin thus it relies heavily on fillets for additional strength (adding additional glue outside the joint)





in the end it depends on the criteria. all glues will glue.
hot glue is crappy heavy. (remember the mantra. don't build planes to CRASH build planes to FLY), but popular due to ease of use & speed.
CA's are great, but expensive & wont last that long and when you need more. you can't just go to mit-mart and grab anything.
Epoxies are great, rediculously strong, but have no give & are heavy if not applied CORRECTLY (not, its really no heavier than PU)
PU's bridge gaps in destroyed foam easily (but begs the question, why not just cut the damaged section out & replace it instead of being lazy & adding weight?) but are such a hassle. expanding, having a short window before denatured alcohol wont dissolve it anymore. high cost, low shelf life.
PVA's... do virtually everything and are cheap. can be a mess because its thin, but cleans up with water. non allergenic. set & cure times are all over the board. titebond can be 10-30 minutes. glue-all can be... hours... becuase they cure by evaporation you can apply heat to speed set&cure. and you can buy a gallon for like 15-20 bucks. a GALLON. lol?









in my case, i went back to being old school. Epoxy in some rare occations and lots of PVA. cheaper, lighter, faster (application of 200-250*F heat will greatly speed set & cure times of both) just as strong or stronger in most cases.
tho i have been known to use hot-glue to tack parts down while PVA sets. (as one would use thin CA to tack balsa parts while another glue sets)
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Old Feb 22, 2012, 10:13 PM
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Beacon's RC FoamTac glue works great. It is a contact cement. The foam will fail before the glue joint fails. In the world of adhesive testing that's called cohesive failure.

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Old Feb 23, 2012, 02:30 AM
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I wonder how the ultra-thin or medium foam safe glue compares to the foam-tac. I the medium stuff has recently become my favorite glue and I'll have to try the thin stuff to see how it is.
Toysrme, that was a great write up! What you said about GG peeling off the foam has net been my experience (at least compared to hot glue). For some reason, I have trouble trusting PVA glue. Maybe it's because I've never used it in this kind of application.
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Old Feb 23, 2012, 03:41 AM
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Also worth adding to Toysrme's write up is that MOST CA glues will dissolve MOST foams in seconds leaving you with just sludge. So in those cases they are the worst possible glues to use .

Also I prefer aliphatic wood glues (like Titebond 2) to plain PVA wood glues (the sort you can get for $15 a gallon ). Still water clean up and set by evaporation so light weight but much quicker setting and sand and take paint rather better. The catch is they're usually yellow so leave unpleasant looking stains if you don't clean them up quickly.

Steve
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Old Feb 23, 2012, 03:46 AM
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Thank you guys for your help!
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