Ian McChesney: We used a grade of stainless steel called Duplex which is resistant to corrosion.
(see right). It's such a harsh environment. You can see sand in the air. If you try to paint anything, it's a disaster. They used Duplex for the Dublin Spire, and Mtech had used it for the streetlights along the seafront, so we had confidence it would work. The benches on the seafront were the first part of the promenade project to be built, using a 316-grade steel, but they are starting to rust, so we had to use something else.
Aran Chadwick: The Duplex was a little bit more expensive, but on a project like this, it doesn't really signify. The raw materials are such a tiny percentage of the project cost. The total cost of the steel didn't come to much more than £2,000.
Why did you choose timber for the bench?
Ian McChesney: We tried to make it in metal, to be more durable. But we were told that the welding might distort the steel slightly. So, we went for oak. I wanted it unvarnished to keep it more tactile, but they've varnished it, because if someone tries to write on it with a marker pen, the ink will sink in.
The steel wouldn't necessarily distort. It would depend on the thickness of the steel and the fixing technique. What's the finish on the ground plane?
Ian McChesney: It's called Addagrip. It's a resin-bonded aggregate that is about 3-5mm thick. It's very lightweight. We couldn't use tarmac as it would have been too heavy. Addagrip is just bonded directly on to the steel sheet with resin.
We had a huge conversation about whether or not we could bond it straight on to the galvanised steel.
We spoke to two different companies. The first one said we couldn't. The second one said: 'Just put an etching primer on it and away you go'. So we went with them.
The base is in pie sections.
When you take a panel off, the break automatically locks on, so there's no danger of a maintenance man getting trapped down there while it's moving. Sand is going to get in there, so it will need cleaning out.
DUPLEX Duplex stainless steel's high corrosion resistance and excellent mechanical properties are a result of its chemical composition and balanced ('duplex') microstructure.
Duplex stainless steels are a mixture of approximately equal volumes of ferrite and austenite crystal structures. The percentage of each element is dependent upon the composition and heat treatment. The primary alloying elements are chromium and nickel.
Duplex stainless steels generally have a similar corrosion resistance to austenitic alloys, except they typically have a better stress corrosion cracking resistance.
Duplex stainless steels also generally have greater tensile and yield strengths, but poorer toughness than austenitic stainless steels.