Voice from the Woods July 2022: Common fence post mistakes

Even though I hadn’t yet touched the posts, the skin on my face began to burn with the vapour in the air. I have since deduced I must be very sensitive to chemicals, as not only did I get burns on the face but I also got burned in one eye. Several weeks later and my vision is still not fully restored.

It’s now nearly two decades since CCA for domestic use was banned and the reputation of green-treated wood in that period has taken quite a battering, largely due to its poor performance as agricultural round posts. Subsequently, small mills producing round posts have been wiped out in preference of imported creosoted posts.

The big mills producing sawn fencing have performed remarkably well as they’ve evolved by using incisor technology to gain improved penetration in wood like spruce, which is notoriously difficult to treat. The smaller mills are simply grading out different types of wood for different applications, which is what I do. Larch heartwood, which is red in colour, as well as both cedar and Douglas fir heartwoods, are all proving to last well, as long as all the sapwood is sawn into other products. Posts made from the heartwood of these trees needs to be fully dried out and seasoned, and the reason they last is quite simple; once the heartwood dries out, as long as it can breathw, it does not reabsorb moisture. Bugs in the ground don’t like hard dry wood; one only has to think of oak posts which are still going strong after 100 years.

Moving on, I’m well aware that problems still exist and more work needs to be done getting timber fit for purpose. However, in view of recent developments I think the whole industry needs a wake-up call, before we end up with legislation which bans any wood that lasts. The common misconception is that wood which is treated lasts and that wood that isn’t treated doesn’t last. There are people out there playing on myths and misconceptions and some who, quite frankly, are being plain dishonest.

For instance, look at the picture of a cross-section of a Douglas fir sawlog. You will immediately identify a dark ring of sapwood circling the log. The dark-red centre of the log is perfect for ground contact once it has been sawn and dried out. Once the moisture has been removed from the red wood it will stay dry, and dry wood doesn’t rot. The outer sapwood ring is a different story. This section needs to be dried out and treated and if creosoted it could last up to 100 years, while the untreated centre may only last 30 years. So, obviously in the days of creosote you wanted the treated sap wood and a perfect illustration of this would be an old telegraph pole where the outer sapwood is still good but the inner core has rotted out.

With modern green water-based treatments a problem exists with the sapwood because the treatment isn’t locking into the cells of the wood. Advice from the WPA (Wood Preservation Association) is to use ‘new generation’ treatments in an identical manner that you would creosote on the likes of pine and redwood sapwood. I feel heartily sorry for the sawmills that followed this advice – often at great expense. A problem exists whereby modern chemicals appear to leach out of the wood and simply wash away in wet weather. Quite often timber which has been treated and dried out (sometimes for weeks) appears to show no sign of treatment. When this timber fails, the WPA, the treatment companies and the angry farmers all blame the sawmillers for not treating the wood correctly. The farmers may have a point, but the other two should be fully aware of the truth. Blaming the sawmills is really their ‘get out of jail’ card – an issue I find disgusting.

READ MORE: Voice from the Woods May 2022: Rising fuel costs and Storm Arwen wasted timber

If we’re not careful, legislation will be introduced that treatment will be required to penetrate to a certain percentage, when the problem really exists not with the heartwood, which can’t take treatment, but with the sapwood, which is well treated. Put in layman’s terms, creosoted sapwood lasts forever; green-treated sapwood can rot in three to four years because of leaching. This is a problem the WPA and the chemical companies won’t accept.

Clearly, research needs to be carried out and an adjustment in chemical composition needs to be implemented. Maybe water repellent needs to be introduced to solve the problem of leaching? If we get legislation, I think the problem will only get worse.

Basically, people who know nothing about timber (heartwood, sapwood, treatments) will hold up timber with poor treatment penetration and accuse the sawmills of cutting corners. In a real-life situation, quite often this wood is lasting, while wood with good penetration is failing. The problem here is with the chemicals – not their application.

To illustrate my point, would you rather have a post cut from larch, cedar or Douglas dried heartwood (even spruce!) with a 20-year lifespan or a pine post produced to the WPA and chemical companies’ guidelines (fully treated all the way through) which is likely to be rotten all the way through within two years and showing no signs of treatment as it’s all washed away?

If you look at the photograph (above) of a well-rotted fence post, it may surprise you that the post is only three years old. I didn’t supply the post, but it came from a batch purchased by one of my customers. At the time he purchased them I remember inspecting them and commenting on the fact that he’d be back in a few years’ time to replace them. I must emphasise here that it wasn’t sour grapes on my part because he’d purchased them elsewhere. 

To all intents and purposes, the product looked impressive and appeared to be at least 80-per-cent treated. 

If I knew nothing about wood (and most people don’t), I’d have been entirely convinced.

It’s heartbreaking to see the product three years later and see the impact the failure of a product like this has on a person’s reputation and livelihood, when all they did was follow the advice of ‘experts’.