Cushion underlay
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Carpet cushion underlay improves the performance of a carpet in several ways.
It provides better impact absorption, sound dampening and insulation against heat and cold.
And in the long term, it significantly increases the carpet's resistance to wear and tear, and helps the pile to recover from the heavy static loading of furniture and other objects.
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The underlay you select for a dual bond carpet installation will depend on its end use and the type of carpet the client has chosen as a covering.
It will also need to be compatible with the adhesive you're using for the job.
Note that cushion underlays used in conventional carpet installations are made in a variety of materials, generally fibre, rubber or foam.
However, for dual bonded installations, particularly in commercial premises, the underlay material needs to be a high-density purpose-made slab foam.
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Classifications
There is an Australian Standard classification for different types of cushion underlay, categorised according to their intended use.
This is set out in Table 1 of AS 4288-2003 Soft underlays for textile floor coverings.
The classification is based on the cushion's performance in compression and deflection after dynamic loading.
A 'dynamic' load (also called 'live' load) is one that is not constant, and includes foot and wheeled traffic.
Below is a summary of Table 1 from AS 4288-2003. Most dual bond carpet installations carried out in commercial premises specify HC underlay.
| Designation | Description of intended use or application |
|---|---|
| LR | Light residential use, not suitable for stairs |
| GR | General residential use |
| L | Luxury use, domestic/commercial where high energy absorption is desirable |
| GC | General commercial use, suitable for normal foot and wheel traffic |
| HC | Heavy commercial use, suitable for heavy foot and wheel traffic and castor chairs |
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Thermal insulation
All underlays provide some level of thermal resistance - that is, resistance to the transfer of heat and cold through the floor. This is measured as an 'R' value.
The higher the R value, the better the material is as a thermal insulator.
Normally, this is directly related to the density and thickness of the underlay.
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Although higher R values are generally a desirable characteristic, it's not always the case.
For example, if your customer has installed an underfloor heating system (also called 'radiant heating'), you will actually want to use an underlay that lets the heat through.
This will affect your choice of underlay material and its R value.
Learning activity
Audio 6 (mp3 |6|KB)Choose one underlay product you're familiar with that is suitable for use in a dual bond installation. Provide the following details:
- brand name and manufacturer of the underlay
- type of underlay and materials used in its construction
- Australian Standard classification
- 'R' value (thermal resistance).
