The Zealandia Blog

An ama-zinc solution for our fence

January 24, 2013

Mark on the fence

Facilities Officer Mark Bathurst takes to the fence

Our resident busy-body, Alfie Kākā, interviews Zealandia Facilities Officer Mark Bathurst and finds out about a generous local company supporting the sanctuary vision and just what Mark is doing up that ladder.

AlfieAlfie: Every time I fly around the valley, I see you on the fenceline tinkering with the fence – what are you doing?

Mark: I’m working on the top hat, or hood, that runs along the top of the fence and prevents any mammal that climbs up the mesh from getting over the top and into the sanctuary. In case you haven’t taken the time to examine it closely: imagine a long steel pipe (diameter 250 mm) cut lengthwise in half. That’s the top hat, and it’s fixed to the top of the fence in sections (the longest measuring 6m) to form a smooth, uniform curve – like upside-down spouting – that mammalian claws are unable to grip. Now, imagine what that means when the fence cannot run straight but must turn a corner. A straight length of top hat must have a wedge cut out of the middle so the two halves can be welded back together at the appropriate angle. But welding damages the zinc-and-aluminium galvanising on the surface of the top hat, meaning the join soon starts to rust unless treated in some way. The earlier treatments haven’t worked, with the result that every top hat angle on the fence (unless recently replaced) has at least some rust, and many have rusted so badly they either have holes in them or soon will do. I’m currently replacing all the angles that have rust holes.

Alfie: That sounds very important. What is so special about the technique you found to fix the rusty angles?

Mark: Previous treatments entailed painting the joins to keep them moisture free. The earlier paints proved not to be up to the job. The last paint we tried – a zinc-rich preparation pioneered by my esteemed predecessor, Dale Burrell – was much more promising, although the angles treated with it have not yet been up long enough for us to know for sure how efficacious it is. The other problem with paint is the need to prepare the surface beforehand, in particular to abrade it by blasting it with garnet so the paint adheres properly. This was extremely time-consuming and the results, despite the genius of Dale’s home-made blastarium, not guaranteed. The new treatment is a far-superior kettle of fish. It’s a whizz-bang industrial process called zinc arc spraying. Pure zinc wire is atomised by a high-voltage electrical current and air-blasted at just under supersonic speed onto the join. Again, the surface of the join is first blasted with an abrasive so that it anchors the zinc, effectively fusing it to the welded steel. But here’s the other great thing: the entire process is being carried out by professionals – a company in Porirua called Steam and Sand. And, what is more, they’re doing it at only nominal cost – because they love Zealandia and are keen to help! At a stroke, their expertise and generosity have rid us of one massive headache.

Mark on the fence

Checking the fit and admiring the zinc.

Alfie: That’s great news! How long will it take you and the crew to finish fixing the angles? Sounds like a Sisyphean task to me…

Mark: Yup, we and Sisyphus are going to have plenty of time to get to know each other – we could be replacing rusty angles ad infinitum. At least our work is more interesting than repeatedly rolling a boulder up hill. I hope to have replaced all the so-called category 1 angles – those that already have rust holes – come autumn. Then we’ll turn to the category 2 angles – those that looked as if they were soon to develop rust holes when we carried out the top hat audit in mid 2012. And after that, I anticipate yet others will have deteriorated to the point of needing to be replaced. And so on! It sounds like a lot of work but our fence is the moat that keeps our mainland island safe, so you could compare it to the processes in other sanctuaries where they maintain a grid of baited traps year-round, run a ferry back and forth every day and so on.

Alfie: Can you tell us more about why the fence is important? It doesn’t stop me flying in and out of the valley on a whim (of which I have many).

Mark: You’re right, it doesn’t. But I hope you realise the danger you place yourself in every time your whimsical nature prompts you to set foot outside the valley. Not to mention those of your ilk who try nesting beyond the fence. You see, my little feathered friend, that fence is what keeps the valley free of mammals such as rats, stoats, possums and cats, which play merry havoc with bird-folk such as your good self – especially those who nest in tree holes, where they and their eggs and nestlings are easily trapped by ravenous, hairy, four-legged beasts with razor-sharp claws and teeth. Were we to let the fence deteriorate, you’d be in big trouble. Be grateful someone’s looking out for you!

Alfie: Thanks Mark and the rest of the team – we couldn’t do it without you!

Steam and Sand

Zealandia would like to thank Steam & Sand for their ongoing support. By reducing the time and cost of fence maintenance we can do more with our resources, continuing to bring the bird song back to Wellington.


You can follow Alfie on Facebook and Twitter to get his latest skraarks.

Comments are closed.