Installation considerations
Tongue and Grooved Timber Floors
T&G timber floors may be fixed to a variety of substrates including timber and steel joists, and to battens or plywood over a concrete slab. Depending upon board width and profile they may be either secret nailed (where the nail is installed within the T & G joint and effectively hidden from view), or top nailed.

For T&G timber flooring installed on a suspended timber or steel framework, the nailing requirements are as per those specified in AS1684 – Residential Timber Framed Construction. The flooring forms an integral part of the framework of the building. It must also have the capacity to span between the joists, with consideration being given to the loads imposed, i.e. commercial loadings or residential loads. Refer to Table 2 for spanning capacity of 19/20mm flooring.
 

Parquet
Parquet is installed directly onto the supporting substrate. The parquet pieces are glue fixed to the substrate in the desired pattern. Key issues for parquet installation include:

1. Slab moisture content: Typically, when tested with suitable measuring instruments, the slab moisture content should measure no higher than 5.5%. Refer to Moisture Control previously discussed.
   
2. Substrate tolerance: No more than 5mm below a straightedge of 3m length, and no more than 1mm below a straight edge of 150mm. Where the slab surface does not meet these requirements it may be either ground or topped with a suitable levelling compound.
   
3. Adhesive: The adhesive must be suitable for the purpose. It must be applied at the appropriate rate, with a notched trowel. Care must be taken to ensure that parquet can be laid before the adhesive skins or becomes unworkable.
   
4. Expansion joints: Expansion joints may be necessary in large areas of floor to allow for some natural moisture driven movement in timber. This movement is across the grain and hence does not impact on the length of the parquet pieces but rather their width. Brick block type laying patterns are the most affected as all the movement will be in the same direction, perpendicular to the length of the parquet blocks. An allowance for movement, typically no less than 10mm, should be made at wall or other structures such as a tile/parquet interface.

Timber Flooring Fixed over Concrete Slab
Timber flooring over a concrete slab can be fixed by means of a sheet floor underlay, typically plywood (12mm minimum thickness), or seasoned timber battens (typically 19mm hardwood). The flooring is then installed in much the same way as for floors on timber joists.

The boards are usually secret nailed in these applications. Where top nail fixing is required, the batten needs to be a minimum of 30mm in thickness to accept the nail. Plywood is not suited for top nailed installations over concrete.

Note: It is good practice to install a vapour barrier (plastic membrane type) over the slab before installing either battens or plywood sheeting. This is a low cost and reasonably effective barrier which will assist in lowering the impact of slab moisture.

Substrate tolerances for a slab surface which supports tongued and grooved flooring fixed to plywood or battens is greater than those allowed for parquet flooring. The acceptable limit for this type of application is a tolerance of 3mm below a 1.5m straight edge. Where tolerances do not meet these requirements, the slab surface may need to be either ground level or topped with an appropriate levelling compound.
 

Figure 14: Fixing layout for plywood under T&G flooring

 

Figure 15: Fixing layout for battens inder T&G flooring

 

T&G Flooring Fixed over Particleboard
T&G flooring fixed over particleboard requires special attention as the particleboard does not provide a suitable base for effective nailing. Acceptable fixing methods are either: nailing through the particleboard into the supporting floor joists so that the nail is adequately embedded into the joist, normally 10 x nail diameter; or alternatively fully glue fixing the boards, generally in association with secret nailing.

Typically, the particleboard will require a light sanding to remove peaked joints and to enhance adhesive bond. Care must be taken to ensure that the moisture content of the particleboard is not above that of the flooring. In many cases the particleboard may have been exposed to the elements during construction and may not have dried sufficiently.

Overlay Timber Floor Systems
Overlay timber floor systems may be fixed in a variety of ways. Some are not fixed directly to the substrate, but rather, each panel or board is fixed to adjoining boards/panels. Some are partially fixed, others are fully glue fixed. In all cases follow the manufacturer’s fixing instructions. These flooring system are not structural, and are laid directly over the substrate. Acceptability of the substrate in terms of level, integrity and moisture content is critical for their long term performance. Typically, constraints placed on overlay floor systems are similar to those for parquet systems.