Police say a critical next step in making the Pike River Coal mine safe to re-enter will be attempted at the weekend.
The bodies of 29 men remain in the West Coast mine after a series of explosions which began on 19 November which has made the mine too dangerous.
Australian technicians will use a foam product to seal surface cracks around the slimline shaft.
Operation commander Superintendent Gary Knowles says the foam expands rapidly to 35 times its original volume and hardens in about five minutes, preventing oxygen entering the mine and stopping gases leaking out.
Superintendent Knowles says this will make machines being used to try to make the mine safe more effective.
Temperatures and toxic gas levels in the mine are continuing to fluctuate.