Every manufacturer publishes installation guides for their underlay products.

You should always follow these recommendations, because they'll not only help you to do the job properly, they may also form part of the warranty conditions.

This means that if there is ever a complaint at some time in the future relating to the underlay, the manufacturer will be on your side as you negotiate a solution with the customer.

Below are some general techniques used to install cushion underlays.

Note that if any of these practices differ from the specific guidelines issued by the manufacturer, you should always follow the manufacturer's advice.

Planning and preparing

The first step in deciding which way to roll out the cushion is to figure out where the seams will fall in the carpet.

Then lay the cushion so that the seams are at 90 degrees to the carpet seams.

If that's not possible and the seams need to run in the same direction, try to keep them at least 300 mm away from the carpet seams.

Make allowance in the width and length of the cushion for trimming it flush with the gripper strip.

If you start by cutting it to the room size, you will have enough allowance for trimming.

Don't forget to include door drops in your measurements.

Manufacturers often specify that the cushion should be unrolled and left to acclimatise in the area where it will be laid.

This allows it to 'relax' as its moisture content adjusts to the humidity of the surrounding air.

Depending on the product and the manufacturer's recommendations, the acclimatisation period might be three hours or even overnight.

Using staples

On wood floors, use stapes to fix the cushion to the floor.

Start with a straight wall and butt the underlay up against the gripper.

If there is no straight wall, lap the cushion over the gripper, staple it in position, and use a knife to trim it.

Smooth out the cushion before you staple it.

You can do this by hand for most materials, but for felted cushion you may find it easier to use a knee kicker.

Use a cushion tape or vinyl-coated cloth tape to cover the seams (other than for fibre underlay).

This will stop any dirt from coming up through the seam and showing as a line on the surface of the carpet.

Using adhesive

On floors where staples are not appropriate, such as concrete, you can use a latex cushion adhesive to fix the material in position.

We will talk more about adhesives in later carpet units in this series.

Calculating quantities

In theory, the amount of underlay you'll need will be the same as the total carpet metreage.

In practice, though, many carpet layers like to estimate the underlay quantity by taking the carpet metreage and subtracting 10%.

This is because you are able to re-use waste pieces without them showing.

However, using small pieces can cause its own problems, so you should still try to keep all pieces as large as possible.