Fence posts, preservatives, et el.

23 Jan 2006
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United Kingdom
I am currently creating a ‘Stockade’ type fence at the bottom of my garden. It’s a joint venture between myself and one of the back-to-back neighbours (our boundary wall was in a dangerous state so we’ve agreed to replace it).

Where possible, I’ll be sinking posts into holes in the ground and setting them in postcrete.

A couple of the posts will be bolted to the neighbours garage foundations using bolt on meta posts.

Finally, where my back garden joins another neighbour’s back garden – which is at a slightly lower level than mine, I’ve used drive in meta-posts. Before driving in these posts, I dug down about 18 inches but was not able to get further down. This meant that on one side of the hole, there wasn’t really sufficient support to hold a post – hence the drive in meta-posts (confused – see diagram below)

OK, to the question(s).

What’s the best preservative to use on the fence posts? I’ve trawled through this site and seen some mention of using bitumen. Is this simply a case of painting bitumen onto pressure treated posts or do I need to preserve them further with a wood preservative – if so, which is best? Overall, the fence is going to be green but if needs must, I’ll use a different colour (black if bitumen) for the below ground level and first few inches above ground.

Secondly, as mentioned, some of the posts will be using drive in meta posts which have sockets some distance below the ground surface. Here is a diagram for help.


The left shows the level of land on my side, the right is the neighbours.

Once the wooden post is in place, is it possible to then concrete over the bottom of the post and the socket. The post will be a six and a half foot post which I think is too big for the socket. This way, there’s 2 foot driven into the ground, and 18 inches sort of supported in concrete – overall the amount above ground would be about 5 foot.

Many thanks in advance

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I don't like putting wooden posts in concrete in the ground. they'll rot, because they're in the ground, and it'll be an awful job to get them out (because of the concrete).

I prefer concrete posts, with dark brown masonry paint to blend them in with the wooden fence.

If you like wooden posts, I'd still try to use concrete repair spurs in the ground, and bolt the wooden posts onto them (wood must not touch the ground).
You see plenty of rotten posts in concrete – as well as plenty of good ones. The rotten ones have generally been put in place and then left – probably with a concave top to the concrete so that water pools against the post. A fence that was put up at my childhood home over 30 years ago is still extremely strong – it has had a coat of creosote on it every other year though.

My preferred method is to creosote a post extremely well, dig a hole, whack the post in, concrete it in with a slope away from the post and the concrete not below ground level. Then, every few years – add further preservative to the visible parts of the fence.

I have a dilemma though. As mentioned, I’ve always used creosote. Is creosote substitute as good? Also, we want the post/fence to be green. Creosote comes in light and dark brown. The question regarding preservative is: is bitumen the bees’ knees of preservative or is it simply a water and air barrier? So, if needs must – I’ll use creosote substitute or bitumen to a few inches above ground level. However, if there is a green preservative that does the job just as well, I’ll use that instead.

Regarding concrete posts – I’ve just taken three of these out of the ground. They were at the part of the boundary where my garden is higher than the neighbours – and they weren’t in place very well. A good shove was all it took to dislodge them – and then plenty of heaving to get them out of the ground. They hadn’t been set into the ground or concrete very well – probably due to the adverse conditions. This is the reasoning behind using the drive in meta posts; the socket may be 12 – 18 inches below the eventual surface but it isn’t half solid. It’s just – what to use to fill the gap. Don’t want to back fill with soil – that is asking for trouble.

Many thanks for your answer.

You're in luck! You're looking for a preservative as good as creosote, and you want your posts to be be green?

one of the finest wood preservatives available is "Cuprinol Green". Several flowing coats, and stand the ends of the posts in it - much better than creosote. It is not cheap - about £20 a gallon - but is very good.

It is so good and so expensive that you can reasonably use it on posts, and timber in contact with the ground, but not on an entire fence.

It does slowly fade in sunlight, and is a wood preserver not a water-repellent stain. If you like you can apply a waterbased waxy green stain from time to time to keep the rain out (after the Cuprinol has thoroughly dried).

(If by green you meant "environmentally friendly" then it is not as polluting as creosote, but it does contain VOCs).
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Many thanks for the answer. I did see ‘Cuprinol Green’ on Cuprinol’s web-site but the instructions it gave were “For wood not in constant contact with the ground”. However, if it’ll do the job – that’s the one for me. Wickes also do their own version – but not in green.

Regarding greenness – it’s green as in the colour rather than green environmentally. I do try to do my bit green wise but realise that there are instances where being green is not the best option for me. I wonder how many VOCs are released when filling a car with petrol (or diesel in my case) compared with the number released when painting a fence. (Off topic a bit)

Once again, thanks for the reply.

this is the stuff


You were thinking of the text that says :

"Small timbers, roof trusses, horticultural timbers: Dip for 3 minutes or brush or spray 2 coats - Minimum 1 litre per 6 sq. metre.
Outdoor or large timbers not in ground contact: Dip for 3-10 minutes if practical or brush or spray 3 coats - Minimum 1 litre per 6 sq. metres. Note: Rough sawn timber will absorb up to twice as much as planed wood."

The instructions used to continue, to say, "for timber in contact with the ground, dip for..." (just checked my can, it says 1 to 24 hours depending on size - allow 40 litres per cubic metre). The idea is to stand the ends in a paint tin or similar to soak it up.
You won't get better than bitumen ... Countryside fencing posts have been preserved this way for decades and they last forever ... Well, almost :LOL:
Seems a similer issue to me,

I take it part of the post will below ground level?
what are you doing about the fence? iss taht all above ground level? and the land drops after the fence? if thats so wont the ground move leaving an increasing gap under the fence?
I saw a gardening program many years ago where the presenter recommended placing a plastic bag over the end of the wooden post before adding the concrete. I can't remember how he finised it off though. Anybody tried this?
Plastic bags are a bad idea as water will get between the plastic and the wood and rot it.
OK, going to put the posts in this weekend. I’m not a slow worker, it’s just I’ve had another major job on (had to have the living room plastered from floor to ceiling – including the ceiling, including first fix electrics and removal of a nailed down floating floor).

Some of the fence posts are going into Meta post sockets but three posts are going to be sunk into concrete. Not sure whether to use Cuprinol Green preservative or Creosote substitute yet – whatever is used would then be covered in bitumen.

First question, where it is often said “Stand the end of the post in wood preservative for X hours”, does this mean the end grain or the whole two foot that is going into the ground? If it is two foot (plus six inches for just above ground level), what does one use as a bucket? I thought maybe stick the post in a watertight rubble sack, and then stand that in a 30 inch length of soil pipe. Only problem is, when you say 4 inch soil pipe, is that the internal diameter? If a wooden pole is classed as 3 inch, I think the diagonal measurement is 4.25 inch so it wouldn’t fit in a pipe. I may even want to use 4 inch poles so, if I need to dip 30 inches of the pole, what should I use?

Second question, instead of using standard posts, I just happen to have a few railway sleepers lying around. We ordered 20 for a raised lawn but the missus has implemented a late spec change so we don’t need that many any more. Sleepers are 8 foot 6 inch long by about 5.5 inch by about 10 inch and weigh between 12 and 16 stone. I need the post above ground to be six foot high so the maximum depth I could bury the ‘post’ would be 30 inches (approx.). The rails of the fence would be secured to the thin side of the sleeper. Can anyone see a problem with this? The sleeper would be secured in the hole with postcrete?

Many thanks

The sleepers are probably already full-cell pressure-treated so will be fairly rot-resistant. If they are full, you will find they bleed tarry black preservative on hot sunny days. They should be plenty strong enough but are very heavy, may need a good foundation to stop them falling over.

I doubt bitumen will stick and harden on wood that is wet with fresh preservative.

If you have the chance of buying preservative in 25litre drums or anything similar, you can stand posts in that to soak. The end grain is definitely where the rot starts. Because I now use concrete spurs and bolt the wooden posts to them (easily replaceable) I never need such a deep soaking bucket.

As far as I know, cuprinol green is a much better preservative than anything else, including creosote or subs.
to protect existing fence posts try this.
Drill a hole halfway into post at 45 degrees just above ground level. Insert a funnel into hole, fill funnel with preservative and let it soak in. Finally place a dowel into hole as a bung. Process can be repeated each year or as necessary. I have not tried it but it sounds OK in theory. I once read that the most vulnerable part of a ground-fast post was the portion just above and just below ground level, that is the part that is subject to alternate wetting and drying.
As far as I know, cuprinol green is a much better preservative than anything else, including creosote or subs.

The old Post Office telegraph poles were treated with creosote (vaccuum rather than pressure treated) - you don't see many of them rotting away and falling over!

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