Marvellous stuff, wood. It can be turned into a desk, a violin or a 50ft yacht. But when it comes to knocking a wooden post into the ground to keep sheep and cattle from straying, things get tricky.
For starters, which type of wooden posts last the longest and what species of tree? Should you go for treated posts or ones that put a layer of bitumen around them?
The choice you make is very important and could mean the difference between posts that last a mere five years or ones that are still going strong 15 years later.
See also: Twelve top tips for perfect fencing
Which wood species lasts the longest?
In the UK, chestnut is reckoned to be the best home-grown timber for posts, though it can be unpredictable.
Larch will last for 30 years, but spruce, on the other hand, is best only on wood that is above ground level. In the US, redwood is thought to be the best wood for posts and fencing.
A shortage of good timber has also meant that Britain has also had to import timber from Scandinavia, Estonia, Latvia and Belarus, which is often reckoned to be denser than some of the home-grown versions.
Bear that in mind when you are choosing fence posts. Don’t buy the cheapest – sweet chestnut stakes and strainers, for instance, don’t need any form of chemical treatment.
HC4/UC4 – What’s that?
For farmers who have had a lot of experience of putting up fences, knowing the best woods for putting in posts is easy. But if you’re new to all this, check what you’re buying.
There are four classes of treated timber, UC1 being the least resilient and UC4 giving the longest-lasting and best protection. UC4 stakes should give you 15 years’ service.
This would typically come from Scots pine or larch dried to 28% moisture content (or less) and pressure-treated to British Standard BS8417.
Creosote and bitumen
Coal tar creosote has been used as an effective preservative for wood for more than 150 years. It deters wood-destroying insects and wood-rotting fungi. However, rules introduced in 2003 meant the public couldn’t buy it any more.
It can be used by professionals and farmers, but you must have a contractor’s log to purchase it.
It’s also important to wear gloves, eyewear and a mask and don’t breathe in sawdust. Don’t burn it either. Wood that is being used in ground contact applications, such as fence posts, is required to be treated to use Class 4/UC4.
Bitumen has been around in the form of natural deposits since the beginning of time and is similar to tar, asphalt and pitch. It does a good job of waterproofing roofs and other things that you don’t want to rust or rot away.
It also does a pretty decent job of stopping fence posts from rotting away.
However, health and safety worries prompted a ban on many existing products in 2005, particularly to prevent prolonged breathing in of the fumes from asphalt or getting bitumen and bitumenous paints on skin.
Equally, if you are removing asbestos-containing bituminous products such as built-up roofing, gutter linings or damp-proof courses, you should use a mask.
One of the clever ideas the industry came up with was incising. This involves using a knife blade to make slots into the surface of the wood and allows the chemical to penetrate about 6mm into the fibre of the timber.
Companies such as Stirlingshire-based Agricision says its fence posts are guaranteed against premature failure for 15 years. The posts are available in 100x100mm and 75x75mm section.
M&M Timber, meanwhile, offers agricised posts with a 15-year anti-rot warranty, kiln-dried to 40% moisture for spruce and 30% for pine. Each post has metal date-tag on it.
Pressure preservative treated timbers
Pressure preservative treatments for agricultural timbers have been around since the 1940s and provide long-term protection against decay and insect attack. The controlled treatment process is carried out in large industrial vessels under a vacuum and pressure cycle.
The wood preservative solution, formulated from copper and modern biocides, is forced deep into the structure of the timbers to provide an effective protection.
Preservatives from different chemical suppliers differ in their formulations and the treated timbers from treatment companies and sawmills are usually branded as either Tanalith/Tanalised, Celcurised, Impralit or Wolmanit treated timbers.
Gloucestershire company Postsaver started making its sleeves in 1994 and now sells to more than 50 countries. A dual layer of bitumen is applied hot and it takes about a minute to apply the sleeve.
You simply overlap the wrap by 3cm or so and staple it to the post with small staples or tack it in place with small round head nails at roughly 75mm intervals, trim with a knife and heat-shrink it in place. Five meters covers 11 100x100mm square posts or 14 75-100mm round posts.
It carries a 20-year guarantee when used on HC4 and UC4 (high-quality) posts. The company says it can be driven into hard, stony ground.
Costs go from a starter pack that includes 5m of wrap at £25 plus a handheld blow-torch. Pretty much any size of post can be accommodated.
Tuffdip is a bituminous emulsion developed by two Herefordshire farmers, which is said to lock out moisture and seal in any chemical treatment. That means the timber remains below the 20% moisture level that makes it less susceptible to fungal decay.
The post can be dipped or brushed to the required in-ground depth plus 100mm. Once cured and hard, the Tuffdipped posts can be driven into stony ground without damaging the moisture resistance.
Tuffdip is also said to be non-hazardous, non-toxic and easy to use. You simply dip for a maximum of five minutes and then allow it to dry. Drying time can be from two hours (in ideal conditions) to 48 hours in cold weather with high humidity.
The company says dipped posts immersed in water for more than a month showed a ground level moisture contents of 20%, whereas conventionally treated posts showed a moisture content of more than 40%.
Don’t let it get frosted, though, as it can become useless. Also, use it up within six months as it can start to separate and the bitumen content will go hard.
These sturdy-looking octagonal Swedish creosote fence posts are imported by Carmarthen-based Davies Implements and claim to have a 25-year guarantee and a life expectancy of 30-40 years. Sizes range from 80×1,600mm and straining posts range from 200×2,400mm.
Farmer case study: David Carbis, Cornwall
Cornwall may be one of the wetter parts of the country, but farmer David Carbis is amazed by how quickly wooden posts rot. He has 100 calves at this time of the year, plus 80 younger stock and 130 fat bullocks.
On his 100ha farm near Truro he found posts had rotted within three years. Even posts left in a shed that had never been put in the ground had started to rot.
He soon got fed up with the costs and decided to use 35mm tapered white plastic posts at a reasonable 90p for a 1m high version. They cost 90p a post and he uses 250 of them a year.
They don’t last for ever (cows tend to flick them off with their tails), but they are quick to replace. He takes them up every three or four years.
There are many good companies selling fencing in the UK with a good track record when it comes to quality. Kent company Jacksons, for instance, has been supplying fencing for farmers for 70 years.
It claims its timber products last for 25 years.
There are many fence systems around, but McVeigh Parker’s Clipex natty fence system is aimed at farmers with long fences. It claims that labour and machinery are reduced, while possessing simplicity and strength, plus a guaranteed life expectancy of 30 years.
Plastic posts are now widely available in 1.8m to 2.7m lengths in three colours and a 1.8m post costs about £15. Are they any good? According to the widely used farmfencetalk.co.uk forum, plastic posts can work, even in hard ground.
The difficulty is that they are quite flexible, said one person, and tend to be weaker than wood at equal sizes. They won’t replace wood, he said, though he could see them being useful across a bog or wet land. They do need a support sleeve, he points out, and are useful for footpaths
One person said he tried pushing a plastic post sideways to straighten it and it broke in the ground. A wooden post would have broken at some point, but the plastic post broke sooner. It is not the easiest task to put in staples either, but they can be persuaded, he said.
Although plastic posts are popular in Germany, they put very little tension on their fences and their posts aren’t driven in very deep.
“The strainer we used was 150mm diameter, reinforced with a moulded in scaffold pole, and it bent. We also found that knocking them in was a bit of a nightmare; once they go off square they start bending and you can’t them back straight,” he said.
When stapling, you need a 30x3mm staple as the material is much more dense than timber and 40x4mm staples bounce off. They are also 50% more expensive than timber, but otherwise OK, said another forum poster.
Fencing contractor case study: Andrew Upson, Essex
Andrew Upson runs Essex Field Fencing, a busy agricultural fencing business at Hatfield Peverel, in the centre of Essex. He has provided a premium service installing field fencing for the past 12 years, and as a dairy and livestock previously, and has more than 40 years’ experience of fencing.
As a one-man band, he makes good use of the latest equipment, including various post-rammers and net unrollers, along with air-powered staplers and nailguns.
He also makes a lot of adaptations to equipment to make them work smoothly and effectively.
He has the latest Bryce tracked rammer, which can put posts into the ground on either side of the machine. The £45,000 machine was built to order and has lots of extras.