Mercer Group shares dropped 17 per cent after the stainless steel fabricator said Fonterra Cooperative Group's final loss from the collapse of a silo it designed and supplied was $20 million.

The company's Mercer Stainless division designed and supplied a silo to TetraPak that collapsed at Fonterra's Edendale factory in September 2016.

At the time, Mercer said the loss could be as high as $45m. It also said it has professional indemnity and public and products liability insurance but that cover would depend on the findings of the investigation and the extent of its liability, if any, as well as the amount of cover and any relevant exclusions.

Mercer said no formal claim has been made by any party against Mercer Stainless to date.

Advertisement

"Liability as between relevant parties has not yet been determined and the investigation is continuing, it said.

The stock dropped 6 cents to 30 cents, having shed 5.3 per cent so far this year.