rated for ground contact?

[pike]

I've come across several books which specify timber which has been treated and is "rated for ground contact". The nearest I've seen to any specification of treatment at b&q is C16 or c32. Is treated tanalised b&q wood ok for ground contact? If not, what do I look for at the timber merchants?

Thanks,
pike

 

[OPJ]

Those C16 and C24 markings are relevant to stress-grading and have nothing whatsoever to do with any kind of treatment. :wink:

Yes, the green, 'tanalised' stuff is what you want. If you make any cuts in pre-treated timber then you effectively break the seal of the chemicals and the exposed section(s) would need to be retreated. You can buy tins of 'end seal' which can simply be brushed on for this.

 

[pike]

Thanks Olly. I do treat the cut ends. I've been using cuprinol which I hope is good enough.

 

[kingcod]

I have purchased tanalised posts and was wondering, along the same lines, whether it would be OK to sink these straight into the ground, do further treatment, and if bedding in 'postcrete' would shorten its life by keeping moisture in contact for too long ....?

 

[pike]

I've done a bit of googling and tanalith appears to be used for above ground and in ground contact. Sounds like it can be high or low pressure treated though. I haven't seen any treated tanalith e wood which specifics to that detail though.

If it's in concrete there should be some drainage (gravel) at the very bottom.

I'm not putting wood in ground contact directly. It's just shims for shed foundations.

I guess old style post and beam uses very durable resistant hard wood.

 

[OPJ]

I guess old style post and beam uses very durable resistant hard wood.

Exactly. Even after treatment, pressure-treated softwood is generally expected to last no more than 10-15 years before it does rot. Regular maintenance could help to prolong this slightly but, ultimately, most people cannot afford to spend hundreds of pounds more on oak fencing.

Most often, rot and decay will occur approximately four-to-six inches above ground level, while the eighteen-inches or so below ground remains durable (initially, at least). That's why you may have seen some fence posts with a bit of black plastic wrapped around the bottom (usually at double the cost of the ones without! :x).