Police say attempts to cap the ventilation shaft at the Pike River mine on Saturday have been unsuccessful and the operation will resume on Sunday.
Low cloud, rain and wind have hampered the capping, which police say is a challenging helicopter operation requiring safe weather conditions.
They say the cap is expected to increase the efficiency of the GAG unit, which is working as normal, and improve the mine's atmospheric stability.
Superintendent Dave Cliff says once the weather allows, they will clear debris at the entrance of the shaft and a helicopter will then lift two semi-circular steel plates, weighing nearly 800 kilograms, into place to seal off the vent shaft.
He says conditions are expected to improve on Sunday.
Twenty-nine men are dead in the mine following a series of explosions since 19 November.