Tips For Working With Self-Leveling Underlayments

A few years back, I participated in a National Tile Contractors Association Installation Seminar.  They had invited a few of us, representing installation products manufacturers, to assist by taking up individual installation topics.

The presentations were supposed to be generic, but a couple of them turned into infomercials.  As a result, I paid little attention to the course section immediately preceding mine.  I was setting up my installation demo, in an area separated by a curtain, from the main room.

At one point, I thought I heard a presenter refer to the need to note in a product file what primer to use with a given underlayment.  I just thought that I probably heard it wrong and dismissed it.  After he concluded, the Moderator called for a lunch break.  I knew most of the attendees and a couple of them came up to me to see what I thought of matching primers to self-levelers.  I admitted that I was not really paying much attention to the last course section and thought that I had simply misunderstood what he was saying.  They confirmed that he had said that you should match a “preferred” primer to a self-leveler.

I explained to them that, with only a couple of exceptions (that I will go over later), the primer selection is predicated on the substrate that you are going over.

  • The primer, that you would use on a cured concrete slab will be different than what you would typically use over plywood and that primer may not be acceptable over a gypsum underlayment.
  • Gypsum sealer/primers are sold as concentrates, calling for dilution rates of between 1:1 to 3:1 (water to concentrate).
  • If you were going over ceramic tile, VCT, terrazzo or a poured epoxy floor, you would probably need a primer that may be much different from one that you would use over steel.

There are also primers that are approved for use over adhesive residues, provided that those residues are non-water soluble.  My experience has been that most carpet and multi-purpose adhesives are water soluble and should be mechanically removed completely, prior to priming.  For the most part, these primers are acrylic and therefore are heavily laden with water.  Some of the water does evaporate, but a lot of it penetrates the substrate; which means that it passes through the adhesive residue, and given the type of adhesive, potentially loosening it up and de-bonding.  At some point, your floor system may no longer be attached to the substrate.

Most manufacturers of self-levelers have primer guides on their website.  I worked for a manufacturer that had eight (8) different primers in our division, with several more available in their concrete restoration group.

Earlier, I had stated that there were exceptions to primer selections based on the substrate rule.  These exceptions are typically when the self-leveler is one that is classified as a topping.  There are toppings that can be polished and others that were developed for heavy industrial applications.  Polishing exerts substantial shear loads on the self-leveler and it is essential that the bond lines from the primer to both the substrate and to the self-leveler be aggressive.  The selection of a primer, in these applications, would favor an epoxy formulation, as opposed to one that is acrylic based.  Many manufacturers continue to call for a sand broadcast (mesh size of between 16 and 30 sand, with no fines) into the fresh epoxy, to refusal, as a method of enhancing the bond line.  Typically, they will indicate a spread rate of 1-lb per square foot.

self leveling underlayments tips
Workers installing a MAPEI self-leveling underlayment

So, when planning to self-level, consider the substrate when selecting the primer and then pick the self-leveler that is designed for the site’s requirements, including depth of pour and dry time.  It should be noted that some self-levelers will allow for the installation of ceramic tile in as little as three (3) hours.  While others require up to a three (3) day wait to install any moisture sensitive flooring.

More on Self-Leveling Underlayments

Ron Gosselin

About the Author:
Ron has over forty-five years of experience in the industry, including Concrete Restoration, Resinous floors, Surface prep, Floor Covering, Tile & Stone and more.

Certifications & Affiliations include:
o CTC registered with the Ceramic Tile Institute of America
o AIA Registered presenter for over 35 Continuing Education Seminars
o Twenty year member of CSI
o Past member of ICRI


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