Newcomers
Bob Underwood Box 40, St. Peters, MO 63376
In modeling, sticking to it is important—in more ways than one! Learning to build and fly (and repair!) requires some dedication and perseverance.
This column is about "sticking" in another way: adhesives.
In the old days, the variety of adhesives available was pretty slim. Even the fastest of these made the building process monumentally s-l-o-w. You could blow on it; you could stare at it; but the stuff just wouldn't dry any faster. Nowadays, don't blink your eyes, because you can glue your finger to your nose in less time.
Adhesives come in a greater variety today, and their uses are much more specialized. Let's look at some.
"White" Glues
This is probably the most generally used family of adhesives. It's also one of the cheaper to use. I place the word "white" in quotation marks because many of these glues are not white in color.
- Aliphatic resins are a beige or tan color. These adhesives set fairly quickly, penetrate the joint better than most, and many sand fairly well. But they are generally somewhat runny and will leave poorly fitted joints and travel to places that don't need to be glued. They are water-based and clean up easily, as long as they haven't set. If you are laminating sheeted surfaces, such as doublers in sheet fuselage sides, this is not your best choice—the thinner sheeting may curl.
- There are specialized "white" glues that are white in the container and clear when set. These adhesives never become brittle but won't sand well at all. They can be used to join varied materials such as plastics as well as wood and are excellent for attaching plastic canopies. They can be thinned or removed with water before they set.
Epoxy
Epoxy is used where high strength is needed—firewall attachment, joining wing sections, fuelproofing, engine and fuel tank areas, etc. It is often used in these critical areas.
- If the mixed material is too thick to paint on with a disposable brush, it may be thinned by placing the mixed material in a container that can be immersed in warm water.
- Epoxy is available in a thinner version called "finishing epoxy." It is sold in two parts, which must be mixed.
- Epoxy comes in versions that set from a few minutes to a half-hour or so. Generally, the slower-setting types are stronger.
Two hints involving mixing:
- Heat will cause epoxy to set faster. (Epoxy also generates its own heat in the hardening process.)
- Use small cups that are not wax-coated for mixing. Small bathroom-type cups work well.
Epoxy does not sand easily, except for the finishing type. It also may prevent some paints or covering finishes from setting if the surface is not prepared properly.
Polyester Resin
Polyester resin is frequently used to attach or fill fiberglass cloth. This is a two-part material: a can of resin accompanied by a small bottle of liquid hardener. The number of drops needed varies; more is not better. Too much hardener causes the resin to set prematurely and may make it brittle; too little and it may not cure.
As with epoxy, resin generates heat as it cures; in large quantities the heat is considerable. Resin sands well. Resin does an excellent job of dissolving foam. So, if you have a foam-core wing, watch out—use cyanoacrylate instead of polyester resin.
Cyanoacrylate
Developed in the early 1970s, the "instant" adhesives (cyanoacrylates, or CyAs) have become a favorite of many modelers because of their setting speed and strength. The early form was the very thin variety, which required a really gap-free fit or the use of fine powder or microballoons to bridge the gap. Thicker versions were later developed to bridge gaps, but that slowed the cure time. Makers then created accelerators that "fire" the adhesive instantly.
Cyanoacrylates have revolutionized modeling—especially field repairs. There are several cautions to be aware of:
- The instant cure and ability to work on many materials means you can easily glue parts of yourself to the model—fingers to nose or ear, etc. Keep debonder handy. If you glue your fingers and do not have debonder, don't try to pry them apart; gently rock them apart—eventually skin oils will allow release.
- Keep the glue away from your eyes. When it "fires" it can give off a puff of smoke and lots of heat; it can burn your skin. Use care when applying CyAs.
Contact Adhesive
Contact adhesive is generally used to attach balsa skins to foam cores or doublers to fuselage sides. It comes in two types: water-based or petroleum-based.
Typical application:
- Spray or brush a coat on each surface.
- Allow the adhesive to dry or become tacky.
- Place the two pieces together.
The adhesion is instant and permanent. Extreme care must be taken to align the surfaces exactly, since you will not be able to shift them or separate them without ruining one of the surfaces or the bond.
If you are using the petroleum-based type, be certain the solvents have evaporated before you place the surfaces together when covering foam. If not, solvent vapors may dissolve the foam and you'll wind up with an empty shell.
Other
There are other adhesives available with special applications that the average newcomer probably won't need. The old-reliable model airplane glues are still around—names like Testor, Ambroid, and Sig-Ment come to mind. These are excellent general-application adhesives: they cure fairly rapidly and are generally inexpensive. They may not be compatible with some materials, especially foam cores.
General Thoughts
- The types of materials and adhesives used today can create compatibility problems. If you have any concerns about possible reactions, always try a test run on a sample.
- Exercise care regarding skin sensitivity and fumes. Some adhesives, such as water-based types, present little concern, but you may be sensitive to resins or other chemicals.
- Experience will help you determine which adhesive best suits a task. The "more is better" rule generally does not apply when joining parts.
- The fit of the parts is important: the tighter the fit, the better. The more dense the wood, the less penetration of the adhesive occurs, especially for rapidly curing adhesives.
- Take care to keep adhesives from causing lumps and bumps under the covering.
When in doubt, check with your local hobby shop or an AMA-chartered club about which adhesive is best for a given use. Gaining from the experience of others is important—but remember some "experts" insist their way is the only way. Don't believe it; shop around for other ideas as well.
Transcribed from original scans by AI. Minor OCR errors may remain.
