Underlay board products
However, it does form the substrate underneath certain types of floor covering, and there may be times when you need to assess it as part of your subfloor inspection.
The main board products used as underlay are hardboard, plywood, MDF and fibre cement.
Hardboard
Hardboard is made from wood fibres compressed into a sheet in a high temperature press.
In principle, the bonding is achieved entirely through the 'felting' process of the fibres and the natural glue, or lignin, already present in the wood.
However, other chemicals can be added to improve the board's strength and resistance to moisture, insect attack and decay.
Fibre cement
Fibre cement is made by bonding cellulose fibres with cement, sand and water.
Traditionally asbestos was used as the fibre reinforcement in 'fibro' products because of its excellent durability and low cost.
However, asbestos fibres were found to cause serious health problems in people who breathed in the dust, and it is no longer used in Australia.
Fibre cement underlay is highly resistant to swelling, shrinkage, fungal decay and insect attack.
Learning activity
When you're inspecting subfloors in older homes, it's likely that you'll come across asbestos fibro sheeting from time to time. Some homes also used asbestos-backed vinyl tiles and carpet underlay. These products are safe while they're left undisturbed, but you need to take special precautions if you plan to pull them up or do any work that might damage them.
We'll look in more detail at how to work safely around asbestos-based products in the unit: Safety at work. But for now, see if you can answer the following questions:
What types of safety precautions are needed to remove asbestos-based products?
Where should these products go once they have been removed?