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Due to the growth of large-format and gauged porcelain tile (GPT), the use of self-leveling underlayments (SLUs) have also become more frequent in tile installations. A properly installed SLU can provide a flat, smooth substrate, ideal for tile. Depending on the need of the project and skill of the applicator, a properly mixed and applied SLU can provide a level substrate, ideal for hanging commercial fire doors and laying out interior walls, in addition to providing an excellent substrate for our tile installation. It is for this reason, that the Materials, Methods, Standards Association (MMSA) decided to pursue an ANSI standard for both the self-leveling underlayment product and installation standard back in 2012.

Listing SLU standards in our own industry’s ANSI documents can be very beneficial to the tile contractor out there fighting for a decent substrate on which to install that large-format 2- x 4-foot porcelain tile. It can also be extremely beneficial for the design professional as standards provide a basis of quality and a proven set of test methods to verify that quality. Reference standards also allow specifications, and those who write them, to remain neutral and refrain from becoming proprietary.

There is a variety of different SLUs available. MAPEI’s Novoplan DPL (pictured) is a deep-pour self-leveling compound. Photos courtesy of MAPEI (Click on image to enlarge.)

For floors, mortar bed installations are a traditional technique for creating a flat substrate with the use of a mortar applied 1 ¹/₄-inch-thick or thicker. Unfortunately, this step is frequently “value engineered” out of projects because concrete contractors don’t want to recess the slab and limited installers have the skill needed to mud a large area. When a mortar bed is used successfully in large or wet areas, the installer has control over the substrate and can prepare a very flat, and if needed, level floor.

When leveling large areas, floors can be prepared much easier and more effectively than walls due to SLUs. The self-leveling market has exploded because of their ease of installation. It is important to note that all installations of self- leveler require the use of a good primer. Some manufacturers make a few different primers, so please check them out and select the one most appropriate for your project. The same can be said about self-levelers -- there is a variety of different SLUs available. Which one should you use? It depends on your site requirements. Do you need something that is fast-setting? Just a skim coat? Are you looking for a leveler with high flow characteristics or one that will accommodate deep pours? One that requires minimal prep?  Or do you just need a competitive leveler?

Other options accommodate other types of applications such as MAPEI’s Novoplan HPL, a high-flow self-leveling compound. Photos courtesy of MAPEI (Click on image to enlarge.)

Please do not misunderstand me; I said that SLUs were easy. They are easy when compared to the alternative -- installing a labor-intensive mortar bed. Self-levelers still require you to select the proper primer and self-leveler for your specific project. There are also some important rules that must be followed when it comes to using SLUs. You must carefully follow the manufacturer’s directions. Do not exceed the maximum thickness recommendations. You must mix SLUs properly. And you must add the proper amount of water. This is critical because overwatering can cause separation of the chemicals, which can lead to a weaker pour with a different dynamic of expansion and contraction, often resulting in a failure. Another component of mixing SLUs properly is to mix them with a suitable drill and mixer or pump. It is usually recommended you do two bag pours if you are mixing in a SLU mixing bucket.

Most manufacturers have a mixing kit that includes a large mixing pail, water buckets, proper mixing paddles, a gauge rake and other beneficial tools. Before attempting a self-leveling project, make sure you have the necessary tools. Self-leveling projects take good planning, proper tools and teamwork because it is best to keep a wet edge when pouring multiple pours in a large area. Have your pour well planned out, who is mixing, who is pouring and who will provide the final finishing?

Self-levelers do not know the topography of the room you are trying to level. You must know the high spots and what it is going to take to get a level substrate if that is your end goal. You must mark what it will take to level, by use of pins, concrete nails in the substrate or caulk lines on the wall.

In addition to mortar beds and SLUs, patching compounds are suitable for localized patches or filling “birdbaths” or dips in the floor. There is a variety of different patching compounds that are fast-setting, moisture-resistant, and that can be applied in thicknesses ranging from skim-coating to very thick, depending on the needs of your project.

There are currently two ASTM standards for self-leveling underlayments: ASTM C1708  C1708M - 19 Standard Test Methods for Self-leveling Mortars Containing Hydraulic Cements and ASTM F2873 - 13 Standard Practice for the Installation of Self-Leveling Underlayment and the Preparation of Surface to Receive Resilient Flooring. A new standard from Materials and Methods Standards Association (MMSA), chaired by Mike Micalizzi with patience and persistence, will be an ANSI standard specific to the installation of self-leveling underlayments for ceramic tile. The proposed standard is currently out for vote to the ANSI committee. We hope that by the time you read this article, ANSI A118.16 American National Standard Specifications for Flowable Hydraulic Cement Underlayment/Self-Leveling Underlayment and A108.21 Interior Installation of Flowable Hydraulic Cement Underlayment/Self-Leveling Underlayment will have passed, and tile installers, estimators and design professionals will begin benefitting from the addition of this complete standard that took so many years to test, complete and adopt.