Once upon a time, when I first started making furniture -steady with the violin there, laddie- practically the only glue commonly available was animal glue, made from cow hides and hooves. This came as hard sheets, or flakes, that had to be pre-soaked and then heated in a double boiler. It stank, and was tricky to use in very cold weather, as it would chill off quickly, sometimes before the joint was completed. There was also glue made from powdered casein, which you mixed with water, but it stained the wood badly. Virtually all that aero modellers had was balsa cement, which was essentially made from cellulose acetate or cellulose nitrate dissolved in mixtures of acetone and toluene.

Then, in the late nineteen fifties came the wonder glue – polyvinyl acetate, or PVA. Actually discovered by a German chemist in 1912, it has been the mainstay of all woodworkers for decades. Being a rubbery synthetic polymer, PVA joints can move, sometimes allowing a joint to “creep.” Its rubbery composition also reduces its “sand-ability,” which can create problems if the timber being glued is soft; the wood sands away quicker than the glue, leaving a slightly raised glue line. Yellow aliphatic glue also became popular, due to its faster grab time, lack of creep and superior sand-ability. Both glues are excellent for aero modelling purposes. I keep a bottle of each. I use PVA for all structural joints that are not seen, the theory being, rightly or wrongly, that its slight flexibility allows some movement when the joint is suddenly stressed. I use aliphatic on joints that will be sanded. Both glues are actually solvent glues, since the water evaporates as it cures. This can cause shrinkage, but also results in reduction of weight as only the solids are left when the glue dries. PVA and aliphatic glues are excellent for all wood to wood joints.

A modified PVA is ‘RC 560 canopy glue.’ As the name suggests, this is the best glue for installing canopies. It sticks to many kinds of plastic, making it dead easy to glue a canopy to covering film or porous surfaces. And it dries clear and cleans up with water.

In the woodworking world, the latest wonder glue is moisture cure polyurethane. Although polyurethane was developed in the 1930s, it is fairly recently that it has been available as an adhesive, the most well known being Gorilla Glue. It will glue almost anything, requires no mixing and cures as a result of moisture in the air acting as a catalyst. It is waterproof, will not attack substrates, has an open time of 30 minutes (meaning the material can be pulled apart and put together again many times during this period without loss of adhesion) and, because there are no solvents it does not shrink. This latter point also means that there is no weight loss as it cures. Because it expands as it cures, you need less glue than you may think. Remember, any squeezed out glue just adds weight, without contributing any real strength. Unlike PVA, polyurethane has a limited shelf life, so for an infrequent user the smaller, although more expensive, bottles are better.

I use polyurethane glue a lot, especially for repairs; it expands to fill the inevitable voids in broken joints that have been reassembled. It is also ideal for skinning foam cores with balsa. Simply spread thinly on the balsa, using the traditional credit card [actually, I use a piece of plastic or balsa off-cut; I have found that the credit card is hard to put through the ATM with glue all over it]. A very light mist of water sprayed on the foam core, or a damp cloth lightly wiped over its surface, encourages the glue to expand, which must result in greater contact area on the irregular foam surface. Apply only enough moisture to be felt when pressed against the face or back of a hand. Then carefully align and fit the off-cut / balsa / core / balsa / off-cut sandwich together and hold down with plenty of weight until cured. Or, of course, you could use the vacuum bagging method.

No model builder would be without epoxy. It is strong, available in fast-cure form and is excellent for field repairs. But, like polyurethane, it has no solvent, therefore can be heavy. Epoxy adhesives are exceptional adhesives for wood, metal and some plastics. They can be made flexible or rigid, fast setting or extremely slow setting. Among common adhesives epoxies are almost unmatched in heat and chemical resistance. Warming the joint will thin the adhesive and encourage penetration in porous surfaces, as well as initiate faster set-off. Just be careful that the glue does not become so thin that it runs out of the joint.

Who has not had at least some experience with the ubiquitous cyanoacrylate, or CA? Cyanoacrylate glue is actually an acrylic resin. Usually a resin adhesive consists of two separate liquids, one called ‘resin’ the other called ‘hardener.’ In the case of cyanoacrylate glue, the hardener, or catalyst, is water. The chemical reaction creates heat, and often this causes a puff of vapour to escape from the joint. Some users are allergic to this vapour, which can cause inflamed sinuses, asthmatic symptoms and so on. Because human skin is naturally moist most modellers have, at one time or another, experienced the frustration of having fingertips stuck together. Although this is annoying when done unintentionally, a form of CA is actually available for medical use, being first used in Vietnam as temporary field sutures.

Another useful adhesive, especially when attaching formers and servo mounts to fibreglass, is RTV [room temperature vulcanising] silicone. It is particularly useful for installing fuel tanks. It will not stick to the polypropylene tank?nothing will?but it conforms to the shape of the tank and makes an ideal semi–flexible cradle to hold it in place.

Then there is contact adhesive. This is available in a spirit solvent, such as Ados, or in a water solvent, such as carpet latex. These are useful for adhering large flat sections to each other; simply apply to each surface and when almost dry but still tacky, position the two surfaces firmly together. I used carpet latex for years when skinning foam wings, but now prefer polyurethane. It is lighter and easier to use. Of course, the above does not represent all the glues available these days. To name a few, there are resorcinol, formaldehyde, polyester, urea, polyethylene hot melt, bone glue, fish glue…the list is endless. No doubt everyone has their own favourite glue, which they will swear by.

Probably the single biggest mistake people make when gluing, is that they apply too much. There should be just enough to result in a very thin line of squeeze-out when the joint is clamped. It is good practice to wipe off this excess before it sets to avoid adding unnecessary weight. Some modellers indicate that they use epoxy for almost everything because of its great strength. But is there any point in having a glue joint that is many times stronger than the material, say, balsa, being glued?

At the end of the day, experience and preference will dictate which glue you use. In any case, nothing is better for a glued connection than clean, tight fitting surfaces, held securely until the adhesive has set off.