BBB Technologies is regularly asked to examine the failure of construction materials, ranging from metals to paints to timber. In this case study, we will discuss a significant timber issue experienced by a reputable timber joinery.

A large joinery shop was contracted to manufacture several hundred exterior doors for a decorous application, which called for the use of facings made from marine plywood glued with resorcinol adhesive. The doors were manufactured and installed, after which they received one primer coat and two coats of topcoat. Within several months, issues arose in the form of coating failure and localised delamination of the individual plies. The doors were replaced at the expense of the joinery, and BBB Technologies was called in to advise.

We attended the joinery to examine the doors, and take samples from various points of the door. 

Marine plywood is manufactured from durable face and core veneers, with few defects so it performs longer in both humid and wet conditions and resists delaminating and fungal attack. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will be from tropical hardwoods and have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Weather and Boil Proof (WBP) adhesive.

The quality of the bonding of the plywood can be assessed in accordance with I.S. E.N. 314 - "Plywood - Bonding quality". Essentially, a sample of the plywood measuring 25 x 50 mm is taken, and small channels are cut into the ply wood to expose the many glue lines bonding the various plies. The sample is then immersed in boiling water for 72 hours, after which it is subjected to a tensile shear test to failure. The quality of the plywood is then assessed through a combination of the shear forces required to cause failure, and the percentage of cohesive failure of the ply. 

Approximately fifty samples representative of the doors which had failed were tested, alongside ten samples of the doors used to replace those which had failed. 

Upon completion of the immersion in boiling water section of the test, it was found that samples taken from the problematic doors had delaminated, with complete loss of adhesion between the individual ply layers. Due to this, the laboratory was unable to carry out lap shear testing. 

Samples taken from the doors used as replacements did not degrade and their performance was consistent with that expected of exterior grade plywood.

A Technical Report was prepared on our findings, and supplied to the joinery. With this report in hand, the joinery sought a claim against the supplier of the plywood. The findings of our technical report was impossible to refute, and the claim was settled out of court. The joinery was compensated for their additional work, and their reputation was restored.

Do you have an issue with the failure of a material? Contact us today, and let our scientific expertise work for you!