Why timber proved tops

The different floor timbers used in the Melbourne Sports and Aquatic Centre include American Maple used in the aerobics area where it was installed as overlay strip flooring that has resilient mounts to dampen imapct loads; Brush Box flooring in the table tennis area where colour, durability and stiffness criteria were important and Tasmanian Oak flooring which was used for the bulk of the project floor material, chosen because there were many precedents for its use, it was available in a large quantity with reasonable consistency and for cost reasons.

The Tasmanian Oak flooring used on the project is 60 x 25mm finished size tongue and groove. The 25mm thickness was chosen to allow two size reductions due to future sanding and refinishing. The end result in years to come will be the thickness of a new standard floor of about 19mm thick.

Twenty two container loads of Tasmanian Oak were provided at the moisture level requested by the supplier. The average moisture content of the floor is 10.5 percent and the flooring is secretly fixed through an extended tongue with crowned staples fired into the tongue recess. These staples are 8mm across the head and act like two brads in their fixing method.

Because the floor area is large, considerable allowance was made for expected movement due to atmospheric changes. Not all movement could be taken up at the perimeter at the walls, so 1.6mm per 1500mm nominal floor width was allowed as a gap within the body of the floor to take up expected expansion. This was incorporated as an open gap produced with 1.6mm thick metal bolt washers used as a spacer during installation. These gaps were kept clear of dust and the like, and after six months in service, most of the gaps closed up and were indistinguishable. The floor perimeter gaps allowing movement at the walls were a minimum of 35mm with a horizontal skirting covering this gap. The skirting also functions as a warning system should excessive expansion occur in the floor. In this case, the skirting would pop off the floor, revealing the presence of excessive expansion.

Before the floor was sanded, a kerosene and water mix at 1:1 proportion was sprayed and mopped over the floor. This technique was used because it provided surface lubrication to help the sanding process; the wet surface helped keep dust down; subsequent dust removal was made easier and the water also helped to disperse the kerosene.

It seems that the main reason for its use was to give a visual indication of any uneven patches on the floor. Sanded timber is light in colour while unsanded sections show up darker.

The applied finish was tung oil, chosen because it is inexpensive and easily repaired; it increases traction under foot; the resultant finish is low gloss for minimal glare, it creates minimum edge bonding between boards and it has little toxicity. An additional advantage of this finish is that it does not need to be stripped as part of any future sanding and refinishing.

For ventilation, forced and natural ventilation occur in the sub-floor space. Natural ventilation occurs through wall vents down one side of the building below the store areas. This is supplemented by a duct and fan system below floor level that runs continuously to move and vent air through the sub-floor area.

Additionally, the building ventilation system draws air throug the floor vents and exhausts out through the roof monitor. This system is switched on only when required by the users.

By this method, a consistent moisture content above and below the floor area is maintained and air freshness is improved, adding to the health and amenity of the space.

This is an edited version of an article that appears on the website of the Timber Research Unit of the University of Tasmania - http://oak.arch.utas.edu.au.