At the southern tip of New Zealand, Invercargill Airport’s complete rebuild occurred in two phases over 18 months with main contractor, Amalgamated Builders, ensuring the airport could operate during construction.

A key feature of the new single-level facility is its magnificent polished concrete floor with its high-gloss finish.

The client was specific about the look they wanted for the floor and they also wanted to unlock the natural beauty of regional aggregates. Consequently, they chose a special mix using black oxide and local aggregates that were sourced by local concrete suppliers Firth Industries.

Once the concrete had been poured, Polished Concrete Limited sought to produce the best polished concrete floor possible.

"To get to what you see in the photos is an involved process. Concrete is a natural material and every floor is unique. The aggregate is unusual as it is a lighter colored stone in a darker background, where most floors are the other way around,” says the director of Polished Concrete Ltd, Jason Torbet.

The original idea for the floor was a salt & pepper ’look but during the process it was decided that a deeper grind was the best option.

There is a real art to getting the best from a concrete floor like this and it was important that Torbet’s team worked closely with Amalgamated Builders to carefully program the various stages of the grinding and polishing.

“Once the building was watertight and the floor was at least seven days old, we can get our large grinders on the slab,” says Torbet. “We now have new remote-controlled grinders that are less physically demanding for my guys and give a more uniform finish.”

It takes three grinds; a coarse, medium and then a fine grind to complete the first stage. “At this point we fill the pinholes in the floor using a polymer slurry and chemically densify the concrete with lithium surface hardeners before we mechanically diamond polish the floor to achieve the shine you see now. We progressively polish several times, finishing at 800-grit in this instance.”

“The last stage of the process is protecting the surface with a lithium surface hardener,” says Torbet. “It has come up great and fits in with the rest of the building, and it’s nice to know it comes from local materials. I have been finishing floors like this for 20 years and have come up with a system and products, that I know work. I think the proof is there to see.”