The selection criteria for an adhesive should take into account the special characteristics of the materials to be joined, the properties of the surfaces at the joint, the strength requirements, the environmental influences to be expected, the weather and temperature fluctuations, the presence of chemicals, the constructional design of the adhesive joint, and the types of loads. In addition, the process of forming the adhesive joint should also be considered at this early stage. Important criteria here are the working time and the way the adhesive is measured out and applied.
The mechanical and thermal properties adequate for the respective application must be clearly defined. Furthermore, an evaluation of the adhesives with respect to their tendency to creep and their relaxation behavior under permanent loading is necessary so that their suitability for systems carrying self-weight can be determined. Beside these important, measurable factors, there are also other aspects to be considered, e. g., appearance and aesthetics. The main assessment criteria for adhesive joints for structural glass and facades include:
– Adequate strength
– Durability (UV, salt-laden and acidic atmospheres, moisture, cleaning agents)
– High stiffness for point fixings
– High elasticity for linear or planar joints between materials with different coefficients of thermal expansion
– Reduced tendency to creep
– Service temperatures from —20°C to +80°C
– Transparency in the case of visible joints
Owing to the large range of adhesives, it is almost always possible to find a suitable adhesive system for the respective application. The quality of the material, the properties, and the internal strength of an adhesive normally vary only minimally across different batches and can be well controlled by the manufacturer. This makes it all the more important to provide a good, reproducible surface quality that enables adequate, good adhesion between adhesive and substrate.