Winstone Wallboards, which controls about 94% of the country's plasterboard supply, has frozen all advance orders for July onwards for the product, as it deals with the construction sector stockpiling building supplies.

In an update to merchants and customers this week, the Fletcher Building-owned company said the September and October lockdowns had caused significant disruption across the building industry.

Fletcher's chief executive for building products Hamish McBeath said despite operating its two plants 24/7, the manufacturer had been unable to make a dent in existing orders.

This has created a backlog of orders to pick up and deliver, resulting in longer lead times which had already stretched out to May.

McBeath said the firm was currently dispatching enough plasterboard every week for the equivalent of 1,000 new average size homes.

"Record manufacturing output, coupled with sourcing some product from an overseas manufacturing source has not been sufficient to keep up with the level of forward ordering and halt the increases in lead times.

"It is not pragmatic for lead times to continue to extend as they are and consequently an alternative approach is necessary."

McBeath said while raw material supply hasn't significantly impacted domestic production, there was some volatility of imported supply as a result of disrupted shipping lanes from the US, China and Australia.

The upshot is that from July, supply of Winstone's two main gib plasterboard products, Barrierline and Weatherline, will move to an "allocation" model to prioritise orders and minimise the number of order changes.

"Effective immediately we will not be accepting or processing new plasterboard orders for July 2022 deliveries onwards."

The company said over the next two months it will provide additional information to its merchant customers, which include major building materials retailers Placemakers, Carters, Mitre 10 and Bunnings as to "how the process will work".  

The move comes as the Commerce Commission begins its market study into the materials industry, in the wake of concerns of an inefficient, monopolistic market, largely dominated by Fletcher Building and timber supplier Carter Holt Harvey.

Fletcher invested $400 million for the construction of a new plasterboard plant in the Bay of Plenty, expected to become operational from the middle of next year.