One of the major advantages of glulam is its freedom from major checking due to the exclusive use of kiln dried lumber in its fabrication. According to CSA 0122, laminations are glued with a moisture content of 7-15% . This approximates the moisture content in normal use and thereby reduces checking. However, some seasoning checks may occur when members are installed under conditions that require rapid adjustment to a much lower equilibrium moisture content.
Rapid changes in moisture content after gluing will result in shrinkage that will develop stresses in both the glued joint and the wood. Differences in the shrinkage rate of the individual laminations tend to concentrate these stresses at or near the glue lines. For this reason, when checking does occur, it is usually adjacent to glue lines. The presence of wood fibre separation in the laminations of checked members indicates that there is adequate glue bond and not delaminating.
Precautions to minimize checking:
- Ensure proper storage (see storage guidelines). This will prevent moisture absorption by the members.
- Consider the environment. Factory applied sealer is applied at a level consistent with normal environments (single coat in side grain surfaces, double coat on end grain surfaces). If the structure is being erected in an area where severe conditions are expected, ordering members double coated is recommended.
- Once a structure is enclosed, temperature should be increased over several days. In dryweather conditions, air should be humidified and maintained at a low temperature over several weeks to promote gradual drying.
- Apply finish. The factory sealer is intended as a temporary protective coating. Once the structure is enclosed, and before any excessive heating, one coat of varnish, urethane, or other undercoating should be applied, then followed by the finish coating in accordance with the architect's finishing schedule.
