Fitting a carpet underlay

Fitting carpet underlay is pretty straightforward for most DIYers. Let's take this step by step:

1. Use the right tools

In any successful carpet underlay installation you must have the right tools. You don't need many but you should use tools specifically for the job. For a conventional "stretch fitted" carpet you will need:

• Utility Knife - for cutting the carpet and underlay.
• Knee Kicker (Carpet Stretcher) - for stretching the carpet over the gripper.
• Carpet Tucker - for creasing and tucking the carpet behind the gripper.
• Staple Hammer - for stapling the underlay to timber floors.
• Hammer - for hammering the gripper nails into the floor.
• Gripper Shears - for cutting the gripper to the correct length.
• Tape Measure - a good quality, domestic metal tape measure will do.
• Knee Pads - optional - depends how strong your knees are!

We even have a Carpet Fitting Kit which includes a Carpet Stretcher, Carpet Tucker and Utility Knife to get you started. You'll be fitting underlay in no time!

2. Preparation

Good preparation is vital:

• When laying any type of carpet or flooring the first thing to do is make sure the sub floor surface is smooth, clean and dry. Sweep the floor thoroughly and remove any nails or material that may be protruding. Use a vacuum cleaner if you need to.
• Remove any doors to the room so you won't have to work around them. This isn't mandatory but it will make things easier, especially when you reach the door jambs.
• Nail your carpet gripper around the edge of the room leaving a gap of three quarters the thickness of the carpet you are going to lay (you will tuck the carpet into this gap, and you want a snug fit). Don't fit carpet gripper in front of your doorway. The gripper has an angled edge on one side - this needs to face the wall. You should be able to read the printing on the gripper as you face the wall.   
• If you have a hard subfloor (such as concrete or tiles) then it may be better to glue your gripper to the sub floor. Make sure your gripper is laid evenly. This is what keeps your carpet in place.
• Now you have everything in place for installing carpet underlay.

3. Laying carpet underlay

• Lay the underlay, ideally, so that it runs at right angles to the direction of the floor boards.
• Lay the underlay so that it overlaps the carpet gripper.
• Rubber underlay should be laid face down with the rubber on the sub floor and the backing facing up to meet the underside of the carpet. PU foam underlay should have the coloured film facing down on the sub floor and the backing facing up to meet the underside of the carpet.
• Lay the underlay in strips against each other tightly - but make sure they don't overlap.
• Staple the underlay down along the inside edge of the carpet gripper.
• Trim the excess underlay along the inside of the gripper and use underlay tape to seal the seams. This will prevent lines showing through to your new carpet and stop the underlay moving when you are laying out and stretching the carpet.

4. Laying the Carpet

A new carpet is a significant investment. If you're in any doubt on how to install it we strongly recommend you contact a professional carpet fitter.

• To install a carpet you need to start with a piece that overlaps the edge of the floor by about 10cm. The overlay can be trimmed later so the carpet fits properly.
• To cut your first section, measure the room at its longest point and add 10 cm to that measurement.
• Mark the back of your carpet at both edges with that measurement and join the two marks with a line.
• Fold the carpet over on itself, and using a straight edge and a utility knife, cut through the back of your carpet.
• Be sure to place a piece of scrap board underneath your cut line to protect the underlying carpet from being cut.

Joining the Seams

• If your room is wide enough that you're going to need another piece of carpet, follow the same process with the second piece - measure, mark and trim.
• Be sure the carpet pile is running the same way in all pieces, and that the carpet you cut is large enough to overlap the wall by about 10cm, as well as overlapping the first piece of carpet by 10cm.
• Try to lay out your carpet pieces so the seams won't be in a noticeable position or in high traffic areas, but obviously sometimes this isn't possible.
• Where the carpet pieces will join, overlap the two pieces, and then using a utility knife or a rented seam cutter, cut through both pieces of carpet, ensuring the edges will match exactly.
• Place a piece of seaming tape (sticky side up) on the underlay where your carpets will join.
• Use a carpet seaming iron to activate the adhesive (the iron goes on the tape not the carpet) lay the edges tightly together and seal the seam with a roller.

Fitting the Carpet

• Attach the carpet along one edge.     
• Put the end of the knee kicker about 8-10cm from the wall and kick your knee forcefully into the padded end of the knee kicker. This will stretch the carpet over the carpet gripper, where the pins will grab it and hold it firmly in place. Then using the carpet tucker push the carpet behind the carpet gripper.
• Work your way around the room stretching the carpet over the carpet gripper, and trim the carpet near the wall with a utility knife or carpet trimmer.
• At the doorway trim the carpet so the edge will be underneath the closed door and install a threshold bar, which will hold the carpet in place at the doorway section.

Fitting carpet on stairs

• Fitting carpet on stairs can be awkward but the same principles still apply.
• Fit a piece of gripper on the tread of each stair so that the angled edge is furthest away from you and also fit a piece on the riser of the next stair so that the angled edge faces the angled edge of the gripper fitted on the tread. Again the gap left really does depend on the depth of carpet to be installed. Three quarters of the depth of carpet is the correct gap. If in doubt try it on one stair.
• Cut the underlay in strips off of the roll about 5mm narrower than your stairs. Starting at the top stair fit and staple the underlay to the stair tread and over the nose down to the next piece of gripper and cut off with a utility knife. Repeat all the way down.
• Measure the width of the stairs and cut the carpet from the length of the roll. Roll the carpet up so that the outside is facing you, then fit from the top stair down tucking into the  gripper recess on each stair, ensuring the carpet is pulled tightly over each nose.
• Cut off any excess carpet.