Various adhesives may be used for glulam. The polycondensation adhesives such as, melamin-resine and phenol-resorcinal resin adhesives harden through the separation of water and are referred to as glues. The polyurethane adhesives belong to the group of polyaddition adhesives.
At the time when this section went to press, the verifications of usability for the adhesives required in the future were still unclear. Presumably, comprehensive supplemental national verifications will be required in the planned residual standard in addition to the verifications according to EN 14080: 2005-09.
The glue-lines are very thin (approx. 0.3 mm), the adhesives are very insensitive to chemical influences (see also the section Additional Characteristics and design properties). Inasmuch as glulam is given a preservative treatment, the compatibility of the preservative agents used and the adhesive used has to be verified. Glulam manufacturers generally do not use all adhesive types for bonding.
Glue / Adhesive Types
|Adhesive Type ||Area of Application ||Color of the glue-line |
|Modified melamine-resin ||inside and outside ||light to brown |
|Phenol-resorcinal-resin ||inside and outside ||dark brown |
|Polyurethane ||inside and outside ||light to transparent |
Modified melamine-resins and phenol resorcinol-resins contain formaldehyde. Because the concentration is low and particularly low-formaldehyde adhesives are used, the expected ambient concentrations are significantly below the limit values given in the Formaldehydrichtlinie (a directive limiting the formaldehyde-emission of wood-based-panels) that applies to wood-based panels (known as E1 class). A publication on this topic can be found in the download area of this homepage.
Polyurethane adhesives are formaldehyde-free. Because formaldehyde is a natural component of wood, glulam made with polyurethane adhesive also contains small quantities of formaldehyde.
Source: Studiengemeinschaft Holzleimbau