We have covered the preparations for subfloors in Section 1 of this unit (Preparing for installation), and the preparations for underlay and carpet in Section 3 (Basic carpet installation principles), including acclimatising them to the room conditions.

Make sure that if an underfloor heating system has been installed, it has been turned off at least 48 hours before you're ready to spread the adhesive, and is left off until the adhesive has set.

We've talked about different types of adhesives available for dual bond installations, and the fact that some people prefer to use a 'pressure sensitive' product to stick down the underlay.

This is an excellent choice for floor coverings that will be subjected to heavy wear and may need to be removed and replaced in certain areas.

Whichever adhesives you select, check that they will be compatible with the materials you're laying, including the heat bond tape that will go under the carpet seams.

Let's now assume that you're ready to install the underlay.

Installing the underlay

If you are not using carpet grippers in this installation, you should trim the underlay to fit tightly around the perimeter walls.

If you are using grippers, see Section 3 on the general installation procedure.

Make sure all underlay seams are butted neatly without any compression.

Fold one half of the underlay back on itself to expose the subfloor underneath. Pour a quantity of adhesive on the floor and spread it with a notched trowel.

Make sure you use the correct trowel size, as specified by the adhesive manufacturer.

Remember to hold the trowel at 60 degrees to maintain the right consistency, and go right to the edges and into corners.

Wait for the adhesive to 'tack up', and then carefully lay the folded-back underlay into position on the adhesive.

Use the same procedure on the other half of the underlay.

Then trim in the underlay around the perimeter.

If you're working right to the wall without grippers, leave a gap to allow for a tuck finish in the carpet.

Use a roller to apply an even pressure over the whole area.

Seaming the carpet

See the lesson page Seaming the carpet for the general techniques used to join carpet seams. The basic principles are the same as for conventionally laid stretched-in carpet.

If you're using a single-sided heat tape, you should spread adhesive underneath so it sticks down onto the underlay.

If you're using double-bond tape, you should only trowel up to the edges of the tape.

Don't forget to apply seam sealer to the join before bringing the two sides together.

Laying the carpet

Cut the carpet oversize, as described in Section 3, and position the seams either at right angles to the underlay seams or offset by at least 300 mm.

Fold back one side of the carpet and spread the adhesive onto the underlay.

Use the same techniques as you did for sticking the underlay to the subfloor.

Note that the trowel size will be different now, and will vary depending on the type of carpet you're installing and the backing it uses.

Wait for the adhesive to 'tack up', and then lay the carpet into position.

Check that the adhesive transfer is adequate by pulling up a small section of carpet and looking at the covering on the backing.

If there is not enough adhesive, increase the trowel notch size and check it again.

Use a roller to apply an even pressure to the whole surface area and roll out any wrinkles.

The carpet manufacturer will specify the most appropriate weight for the roller.

Eliminate bubbles by pressing straight down on the carpet before the adhesive sets.

Don't roll bubbles to the edge.

Repeat the same process on the other side of the carpet.

When both sides are done, roll the whole area from end to end and side to side.

Wait for the time specified by the manufacturer, and then roll the carpet a second time. This could be between 3 and 12 hours.

Allow the adhesive to cure before the floor takes any concentrated loads or traffic. This may be between 24 to 48 hours after installation.