Ground Contact Cedar and Siberian Larch

[Welshie]

Ladies and Gentlemen,

This is my first post on this site so my sincerest apologies if this topic has been discussed previously. I have checked and have not found the answer I'm after.

My question is regarding the use of Native (UK) Cedar, Western Red Cedar and Siberian Larch in ground contact. I intend to use these timbers on Gazebo projects, and I have a particular worry regarding the main posts that make up the structures. I intend to use six 6x6 posts to support the roof of the structures. I intend to place the bases of these posts on a concrete pad (some 3m across) end-grain down. My questions are as follows:

1. Will these timbers require preservative treatment where they contact the concrete base? I'm getting conflicting advice regarding the suitability and durability of the 3 timbers when they're in ground contact.

2. If they did require treatment, what would you recommend as a preservative? It would need to be a commercially available "paint on" product that I would use only on the lower portions of the post where they contact the ground.

My aim is to keep the 3 designs as plain as possible, and hence I don't intend on treating the parts of the structures not in contact with the ground.

Your wisdom/opinions/thoughts regarding this matter would be most welcome.

Many Thanks,
Welshie

 

[jasonB]

I would try and space the engrain off the concrete. Assuming you will need some form a anchor/locating dowel at the bottom of the posts even just a stainless nut & plate washer would give a small gap and stop a lot of moisture being sucked up by the endgrain.

I would also use a preservative like clear Cuprinol five star wood preservative, fill a bucket with it and stand the end of the post in it overnight so it sucks up the preservative, just painting it on will not do a lot.

Having said that I have used sawn green larch (untreated)for decking and not had rot issues. I've also had a couple of cedar greenhouses that stood on concrete edgings for a number of vears without problems

Jason

 

[Welshie]

Jason,

Thanks ever so much - that's just what I was after. I had planned to place the posts on Simpson Strongtie 6x6 bases but found that locating/fixing them accurately was a bit of an issue so had planned to do away with them... The other issue was their costliness.


Once again, thanks for the advice
Welshie