The country's largest manufacturer of plasterboard has had to close its Christchurch plant after a high level of asbestos was found in the roof of the manufacturing building.
Winstone Wallboards, which is a subsidiary of Fletcher Building, says it shut the Opawa Road plant on Monday as a precaution.
The company has stood its 45 staff down on full pay.
It hopes about 20 staff will be able to return to work on Wednesday in a newer part of the plant.
However, the 25 people who work in the manufacturing building could be stood down on pay for several weeks.
General manager David Thomas says the company has known there was asbestos in the roof of the plant built in 1961.
He says the roof needs replacing, which is why the recent testing was carried out.
Mr Thomas says the plant makes 25-30% of national plasterboard production.