Groups and Forms of Adhesives

There are an enormous range of adhesives. The correct type for a particular application will be specified in the relevant repair procedure.

Great care must be taken that only the correct type is used. If an unsuitable adhesive is used on a critical structure, a catastrophic failure may well occur.

The two major groups of adhesives are:

• Flexible
• Structural

Flexible Adhesives

Flexible adhesives are used when some flexing, or slight relative movement of the joint is essential and where high load-carrying properties are not paramount. In general, flexible adhesives are based on flexible plastics or elastomers, whereas structural adhesives are based on resins (the most common ones being epoxy or polyester).

Structural Adhesives

Structural adhesives are primarily aimed at applications where high loads must be carried without excessive creep. Therefore, they are relatively rigid, but without being excessively hard or brittle.

Note: Another group of adhesives is the two-polymer type, which has a reasonably even balance of resin and elastomer, resulting in a flexible, yet fairly strong adhesive.

Adhesive Forms

Adhesives can be obtained in a variety of forms, the most common being liquid, paste or film. Others are those such as the special foaming types that which are used to splice honeycomb sections together. Some require heat for curing, whilst others can be cured by the addition of a catalyst or hardener.