When we’re out on site inspecting wood poles, the assumption is often that the pole will need to be removed and replaced.
However, we’re quite often the bearers of good news.
More often than not, we can save, assess, treat or strengthen a pole and extend its useful life by 10-20 years.
Sometimes that’s simply by testing the pole and proving that, despite what it may look like from the outside, it is still structurally sound and fit for purpose.
At times it means reinforcing a pole that has lost strength but can still be safely retained for another one to two decades.
And sometimes, where the pole remains structurally suitable, we can use boron paste to halt or significantly suppress further fungal decay, allowing the treatment to protect the remaining sound wood. This can potentially give the pole many more years of usable service.
The important thing is knowing which option is right for the pole in front of you.
Decay doesn’t automatically mean replacement
Finding decay is not the same as finding a pole that has reached the end of its useful life.
When we carry out a PASS (Pole Analysis and Structural Security) assessment, we drill three small holes around the pole at ground level, angled downwards at 45 degrees. These allow us to assess the critical area around and below ground line, measuring the depth of sound wood and identifying internal decay.
And if you’re wondering whether drilling inspection holes weakens the pole, research on 92 Douglas-fir utility poles found that drilling up to six 20 mm inspection holes had no significant effect on flexural properties.
We also inspect the pole above ground for other signs of deterioration and damage. The condition data is assessed alongside its actual loading and configuration to establish its residual strength and fitness for purpose.
And this is where the process becomes particularly useful. The holes we use to assess the pole also form part of the treatment process.
After we have assessed the structure of the pole, we backfill the inspection holes with boron paste as part of our standard procedure.
So the process isn’t simply:
Find decay → replace pole.
It is:
Test → understand → treat, reinforce or replace.
That distinction can make a significant difference to the life of a timber asset.
Does boron paste actually work?
There is some very good science behind the use of boron paste as a remedial wood treatment.
Research specifically looking at borate mixtures as groundline preservative pastes for utility poles found that boron can move inwards from the treated surface at protective levels. The researchers found that movement increased with moisture and time. They then concluded that combining borates with different solubilities could provide both relatively rapid protection and slower release to help limit renewed fungal activity.
And this isn’t just laboratory theory.
A USDA Forest Service field study followed remedially treated pine posts for ten years. After 3.5 years, every untreated control post had failed, while the treated posts were generally still sound at groundline after 6.5 and 10 years. In most of the treated posts, borax levels remained above the threshold needed to prevent fungal attack even after ten years.
There is evidence of even longer persistence. A 2023 review of borates in remedial timber treatments reports field trials where boron was still present in Douglas-fir poles almost 30 years after application, supporting its value in limiting fungal attack in timber already in service.
So, yes – there is a strong scientific basis for using boron paste as a remedial treatment for timber decay.
How boron paste works in wood
But there is an important qualification.
Boron is mobile in wood. That is part of what makes it useful. Boron can move beyond the immediate point of application. However, prolonged exposure to moisture can also cause boron to leach from the timber.
That means we would never present boron paste as a magic cure or promise that one treatment will protect a pole indefinitely.
Instead, we see it as one part of a sensible asset management strategy: assess the pole, establish its remaining structural capacity, treat where appropriate, and monitor its condition over time.
And that brings us back to why the assessment matters.
We don’t treat a pole simply because it has decay. We first establish whether it has enough sound wood and residual strength to remain in service. If it does, boron paste can help protect what is left.
If it doesn’t, we can reinforce the pole which can extend the pole life for another 10-20 years. Or, if the pole is decayed beyond treatment or reinforcement, we can advise for it to be replaced.
Boron paste for wood poles in the recreational industry
The same principle applies wherever timber structures are expected to carry significant loads and remain in service outdoors.
Adventure playgrounds, zip wires, climbing structures, outdoor attractions and timber infrastructure all face exposure to moisture and biological deterioration.
For anyone responsible for these assets, the question is much the same:
Does this timber structure still have enough strength to do its job? If it does, what can we do to keep it that way?
That is the thinking behind our approach.
We don’t test a pole simply to find a reason to replace it. We test it to find out what is actually there – and then make an informed decision about what happens next.
Out in the field, the answer is rarely replacement. We keep it simple – and cost-effective – test it, treat it, and keep it in service for as long as safely possible.