bonding

Bonding is the joining of two similar or different types of materials using the properties of cohesion and adhesion. By adhesion we understand the attractive or adhesive force between the adhesive and the materials to which it bonds, whereas cohesion describes the internal strength of the adhesive (cohesive force).

Combination bonding is joining wood with other materials or joining different materials such as metal, glass, natural stone and a wide variety of different plastic materials.

To ensure successful bonding, it is necessary to take a number of influential factors into account – both during and after the joining process. During everyday use, the bond must later be able to resist all kinds of loads and stresses like moisture and thermal stress as well as different mechanical stresses (e.g. compression, tension, shear and peel).

Examples of factors that influence bond quality during the joining process are ambient temperature, humidity, air circulation and the fitting accuracy of the joint. Prior knowledge of the later use of the work piece is therefore key when selecting the right adhesive for the job.

Types of adhesives

Natural adhesives

Protein adhesives

 

Skin glue

Bone glue, fish glue, glutin, casein

 

Resins

Synthetic adhesives

Thermosets

Thermoplastics

Elastomers

Urea resins [3]

Polyvinyl acetates [1]

Silane-crosslinked polymers (e.g. Flextec) [7]

Melamine resins

EVA hotmelts [4]

 

Phenolic resins

Contact adhesives - Polychlorobutadiene [5]

 

Resorcinols

Acrylic dispersions [6]

 

Polyurethane adhesives (PUR)

 

 

Cyanoacrylates

(instant adhesives) [2]

 

 

An extremely high resistance to water and heat, as required for example in boat building or outdoor applications without surface protection, cannot be achieved with the adhesives that are commonly used today in the joiner’s workshop. For such applications, phenolic resins or resorcinol resins are the adhesives of choice. However, they are more difficult to use and can also be harmful to health.

Please also refer to the types of adhesives listed under Construction adhesives.


[1] White glues (= polyvinyl acetates) are thermoplastic dispersion adhesives – also in their fully cured state.
They are excellently suited for all applications in interior finishing work and furniture-making and reach very good strengths. They are easy to use, highly transparent (Pattex Classic) and also feature good storage stability and tool-friendly finishing work. 
However, they should only be used outdoors if the wood surface is sufficiently protected by a coating or adequate structural measures. If in doubt, we recommend using a thermosetting adhesive like PUR adhesives.

[2] Cyanoacrylates are primarily used in the construction of PVC windows. When installing roller shutters, the end pieces of roller shutter profiles are bonded with cyanoacrylates. Furthermore, cyanoacrylates are used for fixing PVC sealing strips in corners.

[3] Urea resins are used almost exclusively for veneering applications today. They feature short press times at temperatures from 85 °C upwards.

[4] EVA hotmelts are used for the machine gluing of edge bands. They offer a broad adhesion spectrum.

[5] Contact adhesives (= polychlorobutadiene or polychloroprene) are mainly used for joining two non-absorbent surfaces, for gluing surface coatings (HPL = high-pressure laminates) on pre-shaped parts and for fixing thick veneer edge banding. In addition, they are used for repairing delaminated edge bands and for fixing edge bands on pre-shaped parts that cannot be applied by machine.

[6] Acrylic dispersions are physically drying adhesives. They are often used as assembly adhesives with joint- or gap-filling properties. Usually, they can bridge up to 10 mm. As they are water-based, any adhesive residues or stains can be easily removed while the adhesive is still fresh. These adhesives require at least one absorbent surface.

[7] Silane-crosslinked polymers (e.g. Flextec® by Henkel in Pattex PL 300) are a new type of adhesive and offer a very broad adhesion spectrum. They feature excellent initial tack as well as high water and heat resistance. These polymers are not only able to join two non-absorbent surfaces, but can also bridge gaps. They can even be used to produce elastic, vibration-damping bonds, for example when fixing stair treads on a galvanized steel construction.