Glue

Hazards

The type of glue is often dictated by the material being worked on. The solvent in some glues will dissolve certain types of foam, while on others it will not stick at all.

Water is another factor, and will easily dissolve PVA, and slowly dissolve several other types of foam-safe glue:

"[For foam] If you want the best bond for use around water, use either Gorilla glue (or any other urethane base glues), epoxy, or if you're really going to get wet, resorcinol is hard to beat." - RCGroups user jrbackus

Common Types

• Gorilla Glue provides a handy quick comparison chart between their two polyurethane products, and their CA, PVA, and epoxy products.

Wood Glue

Polyvinyl Acetate

AKA Elmer's Glue, white glue, craft glue, PVA, Titebond II

AKA Aleene's, Tacky Glue (in a low-water fast-stick blend)

Water-based, nontoxic, adheres to most things.

Not waterproof, and in closed joints, some formulations remain a little bit flexible (this may be desirable).

Somewhat weak hold on EPS

Aliphatic resin emulsion

AKA carpenter's glue, yellow glue, Super Phatic, super-penetrating aliphatic, Titebond I / Regular / Original

Works only on porous materials, not waterproof, fast drying. Nontoxic once cured. Sticks faster than PVA. Not gap-filling

Cyanoacrylates

AKA Crazy Glue, Super Glue, CA

The mainstay of hobby modelling outside aircraft, and popular for wood, but most varieties will dissolve foam. Sticks to most substances, including human skin (Warning: Do not inadvertently merge fingers, bonds very rapidly, used to seal battlefield wounds) , but may have trouble sticking to itself.

CA solvents vary in type and toxicity. Sensitivity to CA solvent vapors (distinct from "allergy" / anaphylaxis) is both common and something that can progressively get worse, with rash and acute respiratory problems. Good ventilation recommended.

CA is often described as "not waterproof" by manufacturers, but it does appear to be on the far side of water resistant, with boats, aquariums, and showers using CA without problem. Note that it must cure completely (24h) before encountering water. (ref). Another source notes that it is *slightly* water soluble, but much more so at high temperatures, so boiling water can be used to remove.

CA can be cured rapidly by an optional spray "activator" chemical, or a little less rapidly by a water spray (this is why it's so good at sticking to flesh), or slowly by just leaving it be. The reaction is significantly exothermic, so large quantities curing in a confined space may cause problems.

Dissolves slowly in acetone, which is recommended for accidental skin contact.

Extremely strong hold, but somewhat brittle, and somewhat more expensive than most options. Wide range of viscosity, with different gap-filling properties.

• Good to Know About Superglue - IPMS Stockholm

Foam Safe

Dries slowly due to non-volatile solvents, remains somewhat flexible. Unfortunately, even more expensive than normal CA.

Polyurethane Glues

AKA Gorilla Glue, Excel

PU glue is water-activated and foams up to 5-10x the previous volume using atmospheric moisture. It sticks to everything. Opinions vary on whether it is good for non-porous air-blocked like foam internal welds, with some commenters claiming it's fine and some claiming it won't fully cure. These may turn on a difference in weather (relative humidity) or technique (how long is exposed to air and thus how much water it absorbs before the parts are joined). After curing, becomes waterproof.

• Other than their core product, Gorilla Glue the brand also sells variants labelled Super (CA), Wood (PVA), and Epoxy, none of which share these properties.

Options

White Gorilla Glue

• "Quick setting, good on EPO"
• Foams a little less than Brown

Epoxies

AKA polyepoxide

Two part solution, epoxide 'resin' and polyamine 'hardener'. Common choice for wood bonding. Removal is described as invariably surface-damaging, but assisted by vinegar & acetone. Sanding it down is very common, and one balsa/epoxy user described how painless it was for him to build up by adding on layers of balsa, and sand back down to the desired shape to repair any damage.

Epoxy is sometimes used with fillers to extend it and modify its properties. With enough filler it can be used as a molding material.

Epoxy is used as the bonding material in fiber-reinforced plastics such as fiberglass and carbon fiber.

Hot Glue

AKA Hot-Melt Adhesive, Glue Gun glue,

Actually a wide variety of chemicals. Safe and sticks to everything but foam. Guns have two settings, high and low, and even low will melt through foam. A base thermoplastic is combined with a number of fillers and solvents. Expect deficits in labeling at most establishments.

• Ethylene Vinyl Acetate (EVA)
• Polyolefins (PO)

• Polyethylene (cheapest sticks are no-solvent PE, requires high temp, low sticking power)
• Polypropylene

• Polylamide (PA)

Nitrocellulose

AKA Ambroid, Duco, Balsa Cement

A favorite glue of wood modellers for many years alongside CA, this works extremely well with porous surfaces like balsa. Is highly waterproof - Ambroid was one of the first plastic adhesives, designed for canoe repair.

The solvent is widely available acetone, and acetone can be used both to adjust the level of viscosity, as well as to dissolve cured joints.

• Is Ambroid gone? - RCGroups

Hide Glue

The dominant choice for modellers up until the last quarter of the 20th century, when nitrocellulose & CA took over, there is a broad body of knowledge around using this for planes in older generations. This is a heat-sensitive binder comprised of processed collagen, closely related to food gelatin, which must be kept warm in order to stay fluid.

Resorcinol-formaldehyde resin

The only FAA-approved option for full-sized wood aircraft back when wood aircraft were actually built for humans, but little-used by anyone anymore because of toxicity and the extreme precision needed in forming the join and cutting matching surfaces. Intolerant of even slight misalignment. Extremely waterproof.

Spray Adhesives

AKA 3M Super 77

Note: Some formulations contain acetone, which will eat EPS/XPS but not EPP/EPO.

• Two formulations of 3M 77 exist

Styrene-Butadiene copolymer

AKA UHU-Por

Silicone Adhesive/Sealant

AKA Liquid Nails, kitchen, window & bath caulk

Remains in a strong hold, but still flexible after curing, sticks to anything, slow cure, starts very tacky. For foam, remains sticky enough to hold but flexible enough that it doesn't tear out chunks, as with some more brittle glues.

One-Part

Absorbs atmospheric moisture as a curing agent

RTV Silicone

Room Temperature Vulcanizing silicone Uses a polymer and an activator, with a catalyst. Vulcanizes (is made into a hard, somewhat brittle rubber) without high temperatures.

Acrylic Caulk

Cheaper alternative to silicone sealant, opaque white

Threadlock

Threadlock is used to secure screws and bolts against vibration. For metals only, the potent solvent will dissolve most types of plastic it touches, not only foam. Loc-tite sells a plastic threadlocker, but it is "basically CA" according to one commenter. Comes in permanent, medium, and light/temporary holds.

Unclassified Fan Favorites

• Beacon Foam-Tac
• Beacon Fabri-Tac
• Homax Welder contact adhesive (may not be available in CA due to toluene) (Works well on EPS)
• Loc-Tite / LePage / 3M - Stik'n'seal (may contain toluene)
• JB Weld
• Sil-Ment, Comet (possibly nitrocellulose?)
• UHU Creativ (same as por?)
• UHU All Purpose
• Liquid Nails Perfect Glue #1 (comment: similar to...
• Loctite Repair Extreme
• Titebond types III
• Amazing Goop

Molding Material

Used for filling and insulating as much as for sticking things together, these need to hold their form and stick without shrinking, rather than holding two rigid parts together with a thin, strong layer.

Blu-Tac

Sold for hanging posters on a wall without fully bonding to wallpaper, this insulating substance has been used for things like protecting cryocooled CPUs. A flexible putty, solvent content takes years to fully gas out and harden it.

Sugru / Polycaprolactone

Great success recently in the DIY/Maker community, this stuff dissolves into a putty in boiling water, has a smooth glass zone where it's moldable but not rapidly burn-inducing, and is a hard white polymer in the normal range of room temperature.

Expanding Foam

Expanding foam is sometimes used to provide compressive strength to a tension skin, and increase resistance to things like tail twisting by removing stretching modes of the fiber. It's also used as a permanent interior mold-form material for composite layup (example). Unfortunately, the results are sometimes difficult to predict.

Links

• Glue - How it Works & What is Best for Different Situations - RCGroups
• Adhesive - DIYFAQ Wiki
• The What and How of Adhesives - Great Planes
• All About Glue - Jeff Whitney
• Eflitewiki Adhesives
• spray foam sealant? - RCgroups
• Micro T-28 glue - RCGroups