Best external finish for elm?

[HamsterJam]

Looking for a bit of advice please…
While sorting out my late fathers estate, I found an almost completed post box project made from 20mm thick elm. I have decided to finish it and put it to use. It will be mounted on an outside wall exposed to the weather. What do you think will be the best finish to help it survive the best the British climate can throw at it please?

 

[Yojevol]

It was not the best choice of species by your father. It's likely to distort and it fares badly with changes of humidity. Almost any finish will delay the onset of degradation to some extent but an oil such as Danish which can penetrate the surface would best.
Brian

 

[sawtooth-9]

Agree, elm may not have been the best choice - but it is a hard dense timber.

If I had to suggest a finish that would survive the ( harsh ) Australian climate :

There are marine epoxy systems of almost water thin viscosity - a couple of coats of this would really seal the grain. However epoxy has no UV resistance, so I would then apply a few coats of exterior urethane varnish. You may need to give a light sand and re-coat with urethane every few years

 

[HamsterJam]

Thanks both. I have some Danish oil and Teak oil already but was also considering whether something like Osmo UV protection oil or an exterior varnish might be more durable (I would need to buy the latter two).