THE LEAD STACK - MOUNT ISA

One of Mount Isa's dominating man made features is the Lead stack. A feat of engineering and construction, it has a fascinating construction history.

This information was comiled by the North West Branch of the National Trust of Queensland.

Contract Engineers:
Tileman(Qld ) Pty Ltd
They are recognised as world wide leaders of chimney construction

Commencement Date: January 1977
M.I.M. surveying the site and excavations, designs and planning. Exhaustive tests both on computer and in wind tunnels done in Tileman's office in Melbourne.

Base Foundations: 18th August 1977
Concrete pur commenced (1600 metres) staff of 23, commenced the assembly of platform upon which all work would be carried out as chimney rose. 

Concret Windshield: 16th December 1977
A further 50 people were recruited including steelfixers, winch drivers, concrete finishers and labourers.

Second lift: All concrete pouring ceased at the height of 30 meters to install two lifts that were to transport men, concrete, reinforcing steel and other materials to the working deck.

First 60 meters: 4th January 1978
Pouring recommenced and proceeded aat approximately 5 meters per day before further interruption

Cocoon Erected: 8th February 1978
A cocoon was needed over the working decks to protect the workers from dangerous gases emitting from both the copper and lead stacks. A side benefit was not the men were able to work in airconditioning.

Halfway mark: 28th February 1978
After the worlds first cocoon was operational on the chimney, pouring commenced this time at approx. 6 metres a day.

Finish Target: 31st March 1978
This target was set and the race was on for the top.

After completion of the windshield, the original gang of 20 specialists remained to erect six platforms and galleries, the steel roof, ladders joing the galleries, the service lift and aircraft warning lights. This was completed by the end of 1978 including the removal of the cocoon and the demolishing of the old lead stack.

STATISTICS

Overall Height: 270 Metres
Diameter at base: 22 metres
Diameter at top: 12.4 metres
Thickness of concrete at base: 700mm
Thickness of concrete top: 235mm
Crushed ice used to stop concrete setting too quickly: 5000 tonnes
Total weight of concrete used: 17,400 tonnes

The highest rise in any one day was 6.63 metres on the 9th March 1978.