Rust is already affecting Eden Park's redeveloped South Stand just four years after it was built - but stadium bosses have described the problem as "minor".
Opened in October 2011 as the centrepiece of the stadium's $256 million redevelopment for the 2011 Rugby World Cup, the stand is just months away from hosting thousands of fans during the 2015 Cricket World Cup.
On Thursday abseiling maintenance workers were using grinders on the metal supports for the sound barrier that wraps around the southern stand. A worker said the team was treating rust spots.
Eden Park chief executive David Kennedy said that the work, which was being carried out by the stadium's builders Fletcher Construction, was "normal stadium maintenance" to "remove a small amount of cosmetic rust on some steel brackets".
The work was being carried out under warranty at no cost to the Eden Park Trust Board, Mr Kennedy said.
"The remedial work is of a minor nature and affects secondary steel work that is not structurally important."
It is understood the work has been going on for at least two months at the cost of tens of thousands of dollars and is far from finished.
An engineering expert with experience in building stadiums, who asked not to be identified as he was not aware of the specific facts relating to Eden Park, said the amount of time it took for a structure to begin to rust depended on the surface treatment applied to the steel.
Most stadiums would be built with a 5-, 10- or 20-year maintenance guarantee.
Mr Kennedy indicated the present work would fully fix the problem.
Fletcher Building representatives did not respond to phone and email messages requesting comment.
A report tabled at a July meeting of Auckland Council's finance and performance committee indicated the stadium's finances allowed for paying interest repayments and operational costs but there was no capacity to "reduce debt further [or] address major maintenance issues".
The trust board will also borrow $1.8 million for an extended sound barrier around the Eastern Stand.
• Workers have spent months treating rust that has appeared on the structure supporting the sound shell on the redeveloped South Stand
• Cost estimated in the tens of thousands of dollars, to be met by Fletcher Construction as stadium is still under warranty
• Eden Park chief says work is routine, minor and cosmetic