What is the most common reason for a glue line failure?

The most common reason for a glue line failure is insufficient glue in the joint. When there is an inadequate amount of adhesive applied, it can lead to a weak bond between the surfaces being joined. For a strong glue joint, it is essential that the adhesive sufficiently covers the bonding surfaces to create maximum adhesion. If the glue layer is too thin or uneven, it fails to fill the gaps and irregularities on the surfaces, which can lead to reduced strength and potential failure under stress.

In contrast, while saturation of the surfaces and the structural integrity of the wood are important factors, they are often not the direct causes of glue line failure. Properly applying the right amount of glue ensures that surfaces are effectively bonded. The surface condition should be clean and free of contaminants to ensure a good bond, but insufficient glue is a more specific issue in terms of preventing effective adhesion. Similarly, the presence of excessive glue may lead to other problems, such as squeeze-out or prolonged curing times, but it is less common as a direct cause of failure compared to insufficient application.