John Green wrote: Coefficients of expansion and contraction differ with the type of timber and the influence of temperature and humidity. Any adhesive used for joint bonding on an aircraft should possess – among other characteristics – a gap filling and elasticity function. If some of the earlier adhesives tended to lack these qualities, then maybe a repetitive cycle of expansion and contraction could account for the failure of joint bonded elements critical to the integrity of the airframe.

You are so right. Problem is that Kaurit W with the bakelite filler added has a joint filling capacity of up to 2.5 mm. It wouldn’t be certified if it had no gap-filling properties… And when applied correctly it is absorbed by the wooden contact surfaces, and the resulting fully cured joint is quite strong and elastic. So in theory quite suitable. However, the process of storing, mixing, applying, clamping and curing the glue joints is somewhat complex when compared to say Aerodux. And with it it is prone to errors, which may only now show when the glue fails with age. Worrying, but with the correct inspection techniques it is not a problem to catch this in time. Problem is that for a wide range of aircraft there is no mandatory inspection program, and many owners/LAMEs are not aware of it either. I understand some TC-holders in Europe are working on an inspection program, but that will not catch all those experimental aircraft…