To get the best results you have to pick the right adhesive for the materials you want to join, and then use it in the correct way. But the range available can make your choice extremely confusing.
The idea of an adhesive is easy to grasp: it sticks things together. In practice, however, there’s a lot you need to know about the different types of adhesive on the market: how each works, what it will (and will not) stick together, how long it takes to set, whether the bond is heat-proof or waterproof, and so on. Equipped with this information, you can then begin to make the correct choice of adhesive type for the job you want to do. Here you will find a brief description of the major types of adhesive, and a table that tells you which type to use to stick various materials together. Remember that adhesives should always be used exactly as directed by the manufacturer for the best results. They should also be treated with respect as they can damage the skin; furthermore, their fumes may be dangeous to inhale and highly inflammable.
1 Animal and fish glues
Also known as ‘scotch’ glues, these are the traditional woodworking adhesives, and come in either liquid form, or as solid chunks or sheets that you have to melt down. They are capable of producing a very strong bond, but have no gap-filling ability, so that woodworking joints must fit very tightly. They dry rather slowly, and are seriously weakened when exposed to dampness, however slight. They have now been almost completely replaced by modern synthetic adhesives.
2 PVA adhesives
PVA (polyvinyl acetate) adhesive is a white liquid which dries clear in under an hour, producing a strong bond within 24 hours. It is now the most important woodworking adhesive indoors, but can be used on most dry, porous surfaces. It is widely employed within the building trade as a bonding agent for concrete, and a masonry sealant. However, PVA adhesives do have limitations. They are not very good at filling gaps, so woodworking joints must have a good fit, and must be cramped until dry. The bond doesn’t stand up well to stress, and is weakened by exposure to moisture. PVA adhesives also have a tendency to stain some hardwoods.
3 Casein adhesive
This woodworking adhesive comes as a powder that you mix with water, and dries to a pale yellow colour. It stands up to low temperatures and dampness better than PVA, and gives a stronger bond. However, it is weakened by water – though its strength returns as it dries out again. It can also take up to 6 hours to set so joints must be cramped. It stains many hardwoods.
4 Resorcinol Formaldehyde adhesive
An excellent woodworking adhesive, giving a strong, rigid, extremely water-resistant bond. The snag is that it comes in two parts which must be mixed together, so some wastage is inevitable. It stains most hardwoods rather badly. 5 Urea-Formaldehyde adhesive Another two-part woodworking adhesive, urea-formaldehyde – often referred to simply as ‘urea’ – is the usual choice for exterior woodwork. As well as giving a very strong bond, and having the ability to bridge gaps, it stands up very well to just about everything the weather can throw at it. These qualities also makes it useful in many indoor situations. Unfortunately, it dries rather slowly and joints must be cramped for up to 6 hours. When used on hardwoods it may stain.
6 Contact adhesives
Normally based on synthetic rubber, these get their name from the way in which they are used. You apply a thin coat to both the surfaces to be joined, allow it to become touch dry, and then achieve an instantaneous bond by bringing the surfaces into contact with each other. The resulting bond will resist being pulled apart, but in time some sideways slippage may occur. For this reason, contact adhesives are not suitable for general woodwork and repairs. Their main use is for sticking down sheet materials such as plastic laminate and cork tiles. Obviously, the fact that the adhesive bonds on contact can cause problems where accurate positioning is required, as you cannot make minor adjustments once the surfaces have been brought together. But some contact adhesives are available which have a delayed action, and so overcome this problem to a certain extent. The petroleumbased solvent used in most brands gives off vapour which is dangerous and unpleasant to inhale, and also highly inflammable. You must be sure to work in a well ventilated area, and, if this not possible, use a water-based contact adhesive instead.
7 Latex adhesives
In many ways these are similar to water-based contact adhesives, except that they use natural rubber (latex), and can either be used as a contact adhesive, or as an ordinary adhesive where you bring the surfaces together while the adhesive is wet. They are a little too expensive to be used on large areas and so are generally used for such tasks as joining fabrics, sticking down carpet, and so on – situations in which the flexible, washable (but not drycleanable) bond they produce is a major advantage.
8 PVC adhesives
These stick flexible PVC. The strong, flexible bond they provide makes them the ideal choice for repairing rainwear, shower curtains, beach balls, and things of that sort.
9 Cyanoacrylate adhesives
These are the adhesives (‘super glues’) once claimed to stick anything to everything in seconds. A cyanoacrylate adhesive will quickly bond a wide variety of materials, but it has limitations. It’s expensive, and although you need very little of it, this makes it impractical to use for anything more than small repairs. Surfaces must be scrupulously clean, and a perfect fit, as it has no gap-filling ability whatsoever. Another point to remember is that when used in industry, cyanoacrylate is specially formulated to stick two specific materials together with a very stong bond. Choose two different materials and you have to use a different formula. What the handyman can buy is a compromise formula, and there are therefore some materials that it doesn’t stick very well. Glass is perhaps the best example. Ordinary cyanoacrylate is degraded by the ultra-violet radiation in sunlight and glass leaves it exposed and vulnerable. As a result, a special formulation for glass has been brought out to overcome this problem.
Another problem is that cyarioacrylate reacts in a rather odd way with water. The presence of moisture actually speeds up the setting process, but, once set, exposure to water breaks down the bond. Finally, an unfortunate side-effect is that cyanoacrylate adhesive has the alarming ability to stick people to themselves or to their surroundings, so it needs to be used with great care. It is not, however, as dangerous as sometimes suggested: a lot of patient work with hot soapy water often does the trick. In summary, a cyanoacrylate adhesive isn’t as ‘super’ as it might appear, but it is worth keeping a tube handy for repairs where other adhesives have failed.
10 Epoxy resin adhesives
These are less convenient than cyanoacrylates as they come in two parts, a resin and a hardener, which must be carefully mixed. But epoxy resin adhesives come closer to the ‘stick-anything-to everything’ ideal. The strong, heat-resistant, oil-resistant, waterresistant bond that they provide makes them a good choice for small-scale repair work involving metal, china, and some plastics, as well as a variety of other materials. The surfaces must be clean, but since the resin will bridge small gaps without losing strength, a perfect fit is not essential. In fact, for repair work, epoxies have only two major snags. One is that they dry to a pale brown colour, which tends to highlight the join, though it is possible to colour the adhesive with dry pigment. The second is that they need a setting time of up to 48 hours. This can be overcome by using a fast-setting formulation, which generally holds within five or ten minutes, but still requires at least 24 hours to achieve full strength. Of course, epoxies can be used for large scale jobs too. The reason why they tend not to be is that they are simply too expensive to use.
11 Acrylic adhesives
This is a two-part adhesive with a difference. It will join the same sorts of material as an epoxy, achieving a bond of only slightly less strength in as little as 5 minutes. You don’t have to premix the adhesive and catalyst before you apply them. Instead, you can apply the catalyst to one surface, the adhesive to the other. And most important of all, the surfaces need not be clean. Even oily surfaces can be joined successfully. But it’s expensive, and it is not yet widely available.
12 Plastic solvent adhesives
Although between them, epoxies, acrylics, PVC adhesives, and cyanoacrylates allow you to stick many plastics to themselves, some require a special solvent adhesive. This works by chemically ‘melting’ a layer of plastic on each of the surfaces to be joined, so that they merge together and produce a ‘welded’ joint rather like the join in a plastic model kit assembled with polystyrene cement. They work quickly, and give strong results. However, you must be sure to match the solvent to the particular type of plastic, and only two solvents are commonly available. These are UPVC solvent adhesive (for unplasticised polyvinyl chloride; used mainly for joining lengths of UPVC drain pipe) and polystyrene cement, mentioned above.
13 Cellulose adhesive
Adhesives based on cellulose aren’t very strong, but they are fairly waterproof and heatproof, transparent when they dry and they do set quickly. They are most useful as an alternative to epoxy resin adhesives, or to cyanoacrylates, when repairing china and glass.
14 Vegetable gums and pastes
Based on either starch or dextrine, two plant extracts, these are useful only for sticking paper and card, and even here, these days, they tend to be restricted to the ‘suitable for children’ market.
15 Specialist adhesives
In addition to the general-purpose adhesives we have mentioned so far, you’ll find a number of specialised adhesives, such as tile and wallpaper adhesives.