Treatment for wood for raised beds?

I am wanting to make raised beds from 8in x 1in rough sawn timber that should be already be treated, but as they are going to be in constant contact with damp soil I wonderif I should give them further treatment. Years ago I used preservative having a low viscosity that readily absorbed into the wood, but the current offerings seem to be more of a surface paint that would not soak in very far. I hope to make 4 - 12ft x 4ft beds.

I have two questions -

1. How long may the (presure?) treated timber last if I do not treat it? Say 10 years?
2. Is there any preservative of low viscosity that will absorb into the wood readily?

Thanks

 

5-6 years max for 4x1 type pressure treated... obviusly thicker will last longer although the end grain may rot.

Preserver (thin stuff!!!!!) ( this stuff is good qulity and often used as a pree treatment to unntreated timber joinery prior to primer):

http://www.screwfix.com/prods/65235/Paint/Wood-Care/Cuprinol-Clear-Wood-Preserver

 

Tanalised timber should last reasonably well, although I would not really like to guess how long.

Any other, after treatment, might help, but my guess is that it would probably only be of use for appearances sake.
Dont think any timber treatment can be relied upon if the timber is in contact with soil.

Not sure 1in thick is really enough though.

 

Pete, I agree, It deffinately needs 2" thick minimum.

My mention of 1" was as I have direct experience of replacing timber edgings failing after 6 years.... just trying to give a tangible life span.

 

Guys couldn't you tack some plastic to the inner edges surely that will last longer than just normal soil to wood no matter what the wood has been treated with? Hel.xxx.

 

Would the wood sweat then?? I've used gravel board along the back of my beds and painted it with the cuprinol paint I had

 

The outer side is exposed so it will still breathe,and the plastic must have drainage holes, the only danger area i think is the base as excess water drains away

 

If timber stays wet for long periods it will rot.
If its in contact with the soil, or a piece of plastic, that is in contact with the soil.
There is not much difference, its still gonna be wet.

Your best chance, I think, is to use as thicker timber as you can afford, and that way the rot will take longer to totally destroy the boards.

Probably the extream examples are sleeper, very thick and full of creosote, would last ages, but probably over the top for what you want.