CTEF Tile Tip: The Basics of Self-Leveling Underlayments

Tools needed to install SLUs.

The term SLU refers to Self-Leveling Underlayment. This product is a great and quick way to flatten most horizontal surfaces prior to installing large format tile (LFT). As you probably already know, large format tile installations (a tile with any one side greater than 15" in length) require the floor to have no more than 1/8" in 10' deviation. This means that the floor will not have any low spots or “bird bath” areas greater than 1/8" deep when measured from the high points on the floor with a 10' straight edge.

Most of us know that the floors over which we are asked to set tile are nowhere near 1/8". Being given a floor within 1/4" would be a gift, but most times the floor surface (substrate) is a mess. If these areas are small, a fast-setting patch works really well. But when the area to be flattened is large or looks like the ocean on a rough day, self-leveling underlayments can save you time and money.

There are five critical components required to achieve a successful SLU installation:

Reading and following the manufacturer’s recommendations sounds like common sense, but unfortunately some tile placers think they know it all and skip this step. SLUs are not very forgiving if not handled properly, so following the directions to the letter is a must-do.
When an installer applies thin set or large and heavy tile mortars, they must be keyed into the substrate with the flat side of the trowel. With SLUs, nothing is keyed in, so it is crucial that the recommended primer be applied. This is so important that the manufacturers may want to consider packaging the SLU and the primer as a unit. This way the installer doesn’t “forget” to purchase the primer.
SLUs are engineered to use a very specific amount of water. Using too much or too little water could be a cause for failure. Accurately measuring the water by using a measuring container is a must.
Mixing the powder and water at the proper speed and for the recommended amount of time also are key components for success.
Using the proper tools is a no-brainer. It makes the job go more quickly and helps to ensure a superior finish. The above photo shows all the components of the SLU tool kit, including the mixing barrel, mixing paddle, measuring pitcher, gauging rake with handle, finishing smoother and spiked sandals.

This combination of knowledge and tools will go a long way in providing quality installations that will stand the test of time.

Scott Carothers is the Director of Certification and Training for the Ceramic Tile Education Foundation headquartered in Pendleton, SC, and is responsible for the creation of the Certified Tile Installer (CTI) program, is involved in the creation of the new Advanced Certifications for Tile Installers (ACT) program as well as providing training to others in the tile industry. He has been involved in the ceramic tile industry for over 33 years and was the owner of a successful retail firm prior to coming to CTEF. He has served as President of the NTCA, Chairman of the NTCA Technical Committee and named the NTCA Tile Person of the Year in 2005. He is a voting member of the ANSI and the TCNA Handbook committees. He may be contacted at 864-222-2131 or scott@tilecareer.com.