Prime a Cement Slab for Self Leveler (LevelQuik ES)

January 1, 2009 | by Fred (email) |

We’re finishing up the 4th quadrant of our basement electric radiant heating installation.  To recap the project, we’re installing electric radiant heating wire over a cement slab in a 1000 square foot area.  After laying the heating element, we’re encasing the wire in 3/8-inch self leveling underlayment (LevelQuik ES), which will be topped with Schluter Ditra, and then with some type of ceramic or natural stone tile.  We divided the room into 4 quadrants (or zones), each with its own radiant system and thermostat to make the job more manageable.

Throughout this project, we never covered the first step of the process for laying the floor, which is to prepare the cement slab for the heating wire and self leveler.  So, here’s that information for those who are considering this project.  If you’re looking for more information on various stages of this project, we suggest using the search feature at the top of our site to locate more articles.

Prime a Cement Slab for Radiant Heat & Self Leveler

Preparing the slab for radiant heat is a simple task.  In fact, the radiant heating element itself dictates no particular requirements.  Only the self leveler (LevelQuik ES) requires steps to ensure a good bond between the underlayment and the floor.  These steps must be taken prior to fixing the radiant heat to the floor.

  1. Sweep the slab to clear all visible debris.
  2. Wash the slab to remove all remaining dirt & residue. If efflorescence is visible, you may also need to use an etching product to remove it.  Home Depot and Lowes sell several etching products.  (Check in the basement waterproofing section).
  3. Paint on a latex primer to seal the slab. LevelQuik ES recommends LevelQuick Latex Primer.  We decided to use the LevelQuik brand product because it was locally available. (see details below).
  4. Allow the primer to dry thoroughly before laying the heating wire. If you’re using the hot glue technique to lay the wire, the glue won’t stick well until the primer is dry.

Why Prime the Slab?

The goal of the primer is to seal the slab and create an adhesive layer for the self leveler.  Sealing the slab is essential to ensure the cement does not steal moisture too quickly from the self leveler, which would cause premature drying and cracking of the leveler, ultimately ruining an installation.

Whatever you do, don’t skip the priming step.  Self leveler is an expensive product.  Latex primer is relatively cheap, and skipping the priming step will almost certainly result in a sub-par installation.

8 Responses
  1. Tom says:

    Hello Fred,
    I have been enjoying your information and how-to’s on levelquick es.
    Here’s my project. Question follows.
    My master bathroom floor is slab. I have glued down 1/4″ cork underlayment as a thermal break (it really stopped the cold coming up from the slab). Now I will lay down the radiant wire mesh. I plan to pour levelquick ES over the wiring before I tile the floor. Now my Question; Do I need to prime the cork underlayment with the latex primer? I read the primer was to keep the moiture from being drawn out too rapidly. Cork is not absorbant. I wondered if it will bond to the cork and I have to think it will. It’s made for underlayment and thinsettting tile,. To prime or not to prime. That is the question. Thanks, Tom Pirch. Lubbock Texas

  2. Fred says:

    Tom, I am not familiar with cork underlayment so take this with the appopropriate grain of salt… That said, I would definitely prime the cork underlayment. Levelquik ES demands the primer and there is no harm in adding it (except for a few bucks to buy it and 15 minutes painting it on). It will seal the cork and serve as a bonding layer for the Levelquik. If you don’t do it and end up with a problem, you’ll regret it and have a huge mess on your hands.

  3. Dale Marcus says:

    I have just purchased a foreclose home which I intend to rehab. I intend to lay down vinyl tiles in the living and dinning rooms. The living room can be viewed from north to south going slightly downhill while the dinning room can be viewed from north to south going uphill. This I was going to level using plywood and self leveling compounds which I don`t anticipate having any problems.
    There is an entrance opening between the living room and the dinning room separated by two interior walls. The problem lies between these two walls where there is a huge hump separating the two rooms The hump itself measures approximately 1 foot wide by 5 to 6 feet long. I`m guessing it is between 1 to 2inches high. How do I eliminate this hump?
    I will appreciate any and all suggestions you can offer.

  4. james says:

    I am planning to place a wire mesh heated floor on my ground level. I was told that I would need to purchase a n expensive product to first put down to prevent the heat from heating the slab, then I was told that heating the slab is a normal process and that the self leveler would suffice. Your insight please.

  5. HANDYMAN51 says:

    Are etching products needed to create a good bond when repairing cracks in a slab floor, or can the areas just be cleaned well with a driveway cleaner?

    • Fred says:

      Are you just repairing cracks, or is it more than that? If you are going to pour SLU, you don’t need to etch, you just need to prime. I don’t know when you would need to etch, unless you saw efflourenscence on the surface.

  6. Tony says:

    My house is built on a slab. I want to convert to hydronic radiant heat which I plan on using 3/8″ pex. My questions are instead of muddying the pex on the existing slab can I use self leaving so I don’t have to go so high? And if yes how do I secure the t pex to the slab so when I pour it don’t move or float?

    • Fred says:

      I have not done this and don’t know if it would be appropriate, but you could hot glue the pex. Once the leveler dries it will be frozen in place. But sounds like you’ll need a lot of leveler and that isn’t cheap!

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