Extending asset life in one of New Zealand’s most challenging environments

At Milford Sound Airport, Downer’s Transport & Infrastructure team has delivered a technically complex pavement preservation project, helping restore and protect a critical airfield in one of the most remote and weather-dependent locations in the country.

More than a decade since its last resurfacing, the runway had begun to experience flushing, where excess binder rises to the surface, creating a smooth and potentially slippery condition for aircraft. Addressing this was essential to maintaining safe operations and extending the life of the asset.

A practical, proactive solution

Rather than undertaking a full resurfacing, the team applied Specialised Emulsion Preservation (SEP), a proactive treatment designed to preserve existing asphalt and chipseal surfaces that are still structurally sound.

SEP works by replenishing binder, sealing micro-cracks, and reducing water ingress, helping to slow deterioration and extend pavement life by 5–7+ years. It provides a cost-effective alternative to resurfacing, while maintaining surface performance and safety.

Delivering in a high-risk environment

Delivering this work at Milford required careful planning and precision. With a narrow weather window and a rainforest climate, the team had to wait for the right conditions to complete the works safely and effectively.

The project included:

• Surface preparation and targeted repairs
• Application of a Grade 6 emulsion seal
• A full SEP treatment across the runway
• Updated line marking to meet current requirements

All works were delivered within a tight closure window, ensuring the airport could return to operation as quickly as possible.

Powered by collaboration

Delivered by Downer’s national specialised team, in collaboration with local crews, the project reflects the strength of combining specialist expertise with regional delivery.

The success of the project was driven by strong teamwork across the South Island Sealing team and national SEP crews. Special recognition goes to Edward Hales and his sealing team, whose high-quality surface preparation enabled a strong final result.

As the Milford Airport team shared:
“Bringing in the Downer team was a great decision for the aerodrome, with specialists travelling from across the country to see the project completed. This collaboration has proven to be very valuable.”

A result that speaks for itself

With the runway operational shortly after completion, the project demonstrates how early intervention and the right treatment can deliver safe, durable outcomes, even in the most challenging environments.

SEP uses advanced emulsion technology, including EnviroShield developed by Road Science, to enhance durability and performance.

Looking ahead

This project builds on our recent work at Hawke’s Bay Airport, continuing Downer’s focus on smarter, more sustainable pavement preservation.

Read the Hawke’s Bay Airport story here: https://downergroup.co.nz/news/smarter-pavement-preservation-at-hawkes-bay-airport/

If you’re looking for a cost-effective way to extend the life of your pavements while minimising disruption, talk to our team about how SEP can support your network.

Contact: Trevor Otton, National Pavement Preservation & Sealing Manager, or Manvir Singh, Contract Engineer