How long will douglas fir posts last untreated?

[Woodworks]

As above really.

 

Last load of firewood had some nice long lengths of douglas that would make good poles for a small shed. Wondering if I give them a good coat of Creosote how long they my last? some are large enough to get a few plank out of as well to make perlins.

[se7enthdevil]

i believe they will last a good decade or longer untreated but i'm sure it will depend of just how protected it is and if it's in direct contact with the ground.

[Woodworks]

Thanks Steve.

10 years would be great but yes they would be sunk into the ground but treated as best I can below ground level.

[Squaredy]

Yes the bits above ground should last decades, depending on design.  Posts sunk in the ground will be rotten in 6 to 10 years.  Unless you can work out a clever way to protect them of course.  If you can bed them in large chippings (like railway ballast) and keep mud and sawdust away then they will not stay wet at ground level and may last better.  If they are embedded in concrete then at and just below ground level they will get wet and stay wet and therefore rot.

[Woodworks]

Sadly the ground is often waterlogged in winter with the water table pretty much at the surface so they will be wet a lot of the time regardless of bedding material. 

[se7enthdevil]

can you soak the DF in oil for a few weeks first?

 

it might stop the water and rot getting in?

[Woodworks]

As I say I can give them a good treatment of Creosote first but they are not dry yet so doubt they will soak up a lot.

[Big J]

The most vulnerable bit is not the bit under the ground, but the point a few inches either side of the surface. Below the ground, the environment is anoxic, and bacterial and fungal attack will be slowed as a result. Above the ground, the lack of moisture will slow degradation, but the bit in between will be the issue. Treat that bit most heavily.

 

Douglas is regarded as moderately durable, so you should be OK for a while. Cedar or larch would be preferable.

[Stere]

Sit the shed up off ground on blocks?

[LeeGray]

Sit some 200mm box section shoes into concrete or bolt to floor then notch the posts into these so they are above standing water height.