Proofing wood resting on concrete and other wood?

As an experiment we are replacing a nominally 6' by 6' fence panel (blown out in the gales, bottom rail rotted away) with lengths of 6x2 laid on their side.

So that would be 12 lengths of 6' long 6x2 all laid on the side and stacking up between the concrete fence posts.

We did similar with concrete gravel boards for the first two panels by the house, and this has worked well but we aren't keen on a 100% concrete look all the way down the garden.

So we have these 6x2 lengths, with one 2" side down and the other up. The gaps are where water collects and rot sets in over time. Any recommendations about what to put in the gaps?

Could be silicone sealant, could be black mastic or some other kind of sealant which would fill the space and repel water. Could be in a tube for "gunning" in or in a pot to paint on.

The nice thing about this strategy is that you can fit the lengths of 6x2 one at a time, instead of the usual game of holding a 6x6 fence panel up in the air in a gusty wind to get it over the top of the 6' concrete posts. You should also be able to take it out again and replace, for example, just the bottom one if this has rotted.

Cheers

Dave R

If you don't do something to let some of the wind through you will probably regret it when a serious storm hits it square on.

My instinct would be to leave a small air gap ~1cm between each board so that wind can get through and dry the wood out after rain.

That or use opepe which can survive almost forever wet even in direct contact with the soil. My parents fences were made of it (offcuts from dyestuffs industry filters) and were still fine 40 years later.

There is one minor snag. Its brittle and you can't nail it. Bright orange when new but ages to a soft silver colour by oxidation.

I'm not worried about the wind blowing it over. The wood is 2" thick and between concrete posts.

Leaving a gap is a possibility apart from the contact points between the spacers and the "joists" to create the gap. 10mm would be a significant gap, but I'm not convinced that it would allow enough air through to make a major difference in the wind loading.

Opepe looks interesting but I suspect that it may be expensive. At least, significantly more expensive than lengths of 6x2 from the local Builders' Merchant.

Thanks for the suggestions, though.

Cheers

Dave R

Depends if you can find somewhere locally that has it in offcut sizes. It is sufficiently difficult to work with that scrap pieces can end up as firewood. But if all you are doing it cut to length and slot it in...

David explained on 27/02/2020 :

The best strategy is to not allow the wood to be in direct contact with the ground, or other wood. Space them of the ground and space them from each other, so air can pass through the gaps and quickly dry them. Rigid plastic tube or rod, positioned at right angles to the wood.

Remember to leave gaps for Hedgehog Highways though! Brian

I was discounting that and looking for either a gun on mastic or a paint on underseal to fill in the gap and prevent water entering.

This may, of course, prove to be ineffective over time, but the first fence panel replacement is a trial run to see if we can get an acceptable result. In which case we will do the other panels for a long term heavyweight solution.

The idea is to do away with fragile fence panels and have a more robust barrier which will also heat up in the sun and throw some heat back. Low maintenance over the long term.

Cheers

Dave R

In message snipped-for-privacy@mid.individual.net>, David snipped-for-privacy@btinternet.com writes

Concur with much of the above. You need air movement and no contact with soil to maximise softwood life.

Green (spit) treated softwood fencing rails

Use your concrete gravel boards to keep any timber at least 6" above soil level. At 6 foot, lengths of softwood will move (warp and bow/twist). Tacking on vertical stiffeners would allow you to get away with 38mm and arrange the air gaps others have suggested while minimising movement.

Larch is said to be better provided there is no soil contact but I have no personal experience.

Vertical stiffeners were in the plan, not least to allow attachment of climbing plants.

Interesting thought that the joists could be spaced then fixed in position which allows removal of the spacers and air flow without the spacers themselves becoming a source of water trap and rot.

The first lot of timber has been delivered in the pouring rain and so is drying out a bit under cover.

Cheers

Dave R