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Competencies covered

MSFFL2017: Install carpet cushion underlays and gripper accessories

MSFFL2018: Install unpatterned tufted and bonded carpet floor coverings

Properties and classifications

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Carpet cushion underlay improves a carpet installation in several ways.

The cushioning layer helps to:

  • protect the carpet pile from being crushed under furniture and heavy objects

  • maintain the carpet's texture

  • provide an extra layer of insulation from the cold or heat

  • improve the sound absorption of the carpet

  • give the carpet a softer feel underfoot
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Some people think that if you increase the pile weight of the carpet, you can get away with not using a cushion underlay at all.

But that doesn't take into account the fact that cushioning improves the carpet's resilience and resistance to pressure.

This will reduce the loss in pile height thickness as the carpet wears over time.

So in practice, a carpet installation that includes a cushion underlay is often more economical over time than one without a cushioning, because the carpet will retain its appearance and softness underfoot for longer.

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Thermal insulation

All cushions 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.

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 means you will need to choose a thinner cushion, such as flat cellular sponge rubber or synthetic fibre cushion.

Before you decide on the most appropriate underlay to use, always check to see whether the rooms you'll be laying carpet in have an underfloor heating system.

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There is an Australian Standard classification for the different types of cushion underlay, categorised according to their intended use or application.

This is set out in Table 1 in 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.

Note that a particular classification for a cushion does not mean it can't be used in a different application.

For example, an underlay classified as 'luxury' could be used in a commercial application where extra comfort or firmness is required.

Below is a summary of Table 1 from AS 4288-2003.

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DesignationDescription of intended use or application
LRLight residential use, not suitable for stairs
GRGeneral residential use
LLuxury use, domestic/commercial where high energy absorption is desirable
GCGeneral commercial use, suitable for normal foot and wheel traffic
HCHeavy commercial use, suitable for heavy foot and wheel traffic and castor chairs

Learning activity

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Choose a specific cushion underlay that you have installed at one of your jobsites. Look up its specifications in the manufacturer's datasheet or on their website.

Write down the brand name of the product, the manufacturer, and any other technical details that relate to its properties and classification.

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