Modern adhesives have not only revolutionized many manufacturing processes by eliminating the need for welding, riveting, bolting and other long-standing assembly techniques, they have also done almost as much for the do-it-yourselfer.

Amazingly versatile, today's spaceage glues and adhesives make it easy for the do-it-yourselfer to successfully complete seemingly "impossible" repairs, and simplify many projects that require joining parts made of metal, wood, pastic, glass and other materials.

But there are so many new products that the bewildered consumer often doesn't know which product to use. While it is true that many multipurpose products can be used to bond many different kinds of materials, there is still no truly universal adhesive that can be used for everything under all conditions.

How can you select the adhesive that will best suit your needs for a particular job? By familiarizing yourself with the types used most often for general-purpose work around the house, and by learning something about the principal characteristics and limitations of each.

The most useful and easily available brands fall into several categories, most of which are described in the accompanying chart. No attempt is made to list the highly specialized types that will be needed only for specific projects, but the adhesives described will probably take care of all the gluing and bonding problems the average homeowner or do-it-yourselfer is likely to encounter.

In choosing and using any adhesive, the first consideration is selecting one that will bond the particular materials you are working with, especially if there are two different kinds of material involved. For example, many adhesives will bond wood to wood or wood to leather, but not all will bond wood to metal and glass (epoxy, urethane, silicone rubber and the two-part "instant" will).

The second consideration is whether the adhesive requires clamping to insure a good bond; sometimes clamping is difficult or impractical. Generaly speaking, all wood glues require clamping, as do clear plastic cements, vinyl repair cements and urethane glues listed in the chart.

Epoxy, on the other hand, requires holding or supporting the parts so they remain in position and in good contact. The "instant" adhesives (both the one-part and the newer two-part) require no clamping -- just finger pressure for a minute or so. Contact cement bonds instantly without any clamping as long as both surfaces are completely coated, and after both coats have been allowed to dry before being brought together.

Another important factor to be considered in selecting an adhesive is whether the joint will be subjected to a great deal of dampness or moisture. Some adhesives can take continuous exposure to moisture, while others cannot withstand even a moderate amount of dampness (the label should spell this out clearly).

When assembling wood joints, for example, white polyvinyl glues will work well for most indoor projects, but the newer aliphatic types (slightly darker in color -- a pale yellow or very light tan) will have greater resistance to dampness and humidity, and will form a stronger joint than the conventional white glues will. Where maximum resistance to moisture, as well as maximum strength, is required in a woodworking joint, plastic resin glues should be used (these are powders that must be mixed with water before use).

For bonding other materials where a waterproof, weather-resistant joint is required, epoxy adhesives often provide the ideal solution -- especially for such hard-to-glue materials as metal, glass, ceramics, masonry and many plastics. Epoxies, which come in tubes, jars and hypodermic-type dispensers, are two-part compounds that must be mixed just before use. Some come as a puttylike compound principally intended for filling in and building up broken or missing parts, while others are liquids primarily intended for bonding or joining. Both types have strong bonding qualities and exceptional resistance to moisture, most household chemicals, oil, grease and other solvents. The joints formed are generally not flexible.

The new two-part "instant" glue (Depend, made by Woodhill Chemical, and currently the only brand on the market) is said to be almost as strong and waterproof as the epoxy adhesives. It is a two-part adhesive but does not need mixing. You brush one part on each surface; the cure does not start until the two parts are brought together. However, contact cement is only a moderate-strength adhesive intended for jobs where little stress will be encountered (bonding plastics laminates to plywood or hardboard is the most common use).

Other adhesives, such as the instant one-drop adhesives and the clear vinyl or plastic cements, dry in a minute or two; you can hold parts together with your fingers while the adhesive sets, then put them back in service almost immediately. (Caution is required with the instant cyanoacrylates: These will bond to skin as well as many other materials, so keep it off your fingers and away from eyes and face.)

Adhesives also vary in how effective they are at filling gaps and voids in joints when parts don't fit together neatly, or when pieces do not mate perfectly. Epoxy cement, silicone rubber adhesive and urethane glue (Dow is currently the only brand on the market) do a good job of filling voids, but plastic resin wood glues, and contact cements require snug-fitting joints with few, if any, gaps to form a strong bond.