A customer reported a problem with Le Tonkinois not drying.
He was using epoxy on a teak rudder. He confirmed the epoxy was the correct mixture and dried perfectly. He had sanded it back and then varnished. The rudder was in a dry heated workshop and it was still not dry after 10 days, leaving patches all over of very tacky varnish.
Le Tonkinois applied over epoxy is not usually a problem and tests revealed the varnish dried normally on plain timber.
An experienced boat builder confirmed our suspicions that epoxying teak was the cause.
He described applying epoxy to teak as "a recipe for disaster."
Unless the teak is thoroughly scrubbed with something like acetone to remove completely the natural oil in the wood it may contaminate the epoxy. Varnish applied over this has no chance of surviving for a reasonable time.
Even if this contamination does not happen the grip between the epoxy and the teak is not very strong, leading to a tendency to separate at the edges or at sites of damage.