SLC: Everything You Need to Know for Your Floor-Heating Project

Confused about SLC or intimidated by how to use it? You’re not alone. When planning your floor heating project, you’ll come across terms like self-leveler, concrete and mortar. But what are they, how are they different, and what do you need to know about them for your electric radiant heat project? Read on for our answers to these commonly asked questions about this essential and surprisingly easy-to-use material – no cement mixing truck required.

What is self-leveling concrete?

Self-leveling concrete (SLC) is a viscous, pourable substrate material that contains polymers. It’s used as an underlayment for tile and other flooring types that require a smooth and even surface and to cover irregularities in a subfloor. It can also be used as a topping over concrete slab surfaces to add color and shine. For most electric radiant heating projects, it’s primarily used as an underlayment for pouring over and protecting heating wires and mats before adding flooring to the top.

What’s the difference between self-leveler, concrete and mortar?

Self-leveler is a catch-all term for self-leveling concrete (SLC) and self-leveling underlayment (SLU). There are many brands and proprietary variations in material for each. But for electric radiant floor heating projects, these polymer-based products function the same way. SLC/SLUs need little water and only a small mixer – usually mounted on a power drill – to become pourable. The polymer base ensures that the sand particles remain uniform throughout for a more consistent product.

Cement, or portland cement, is a crushed-rock material made from clay and limestone that is fired in a kiln and fused at high temperatures. It’s an important ingredient in both slab concrete and mortar.

  • Concrete is portland cement mixed with water and sand or gravel. This type of concrete is used for pouring slabs for basements, driveways and foundations. Unlike SLC/SLU, concrete requires a lot of water to become spreadable. It also requires an industrial (and usually large) mixer, like a large drum or cement truck, to keep the concrete uniform and prevent larger sand or gravel particles from sinking to the bottom.
  • Mortar, also called thin-set mortar, thin-set concrete, or thick-bed mortar, is a portland cement-based product that, like slab concrete, requires more water to become spreadable. Instead of mixing with large gravel, mortar contains fine sand particles for a thin, uniform surface. Spreading thin-set over a subfloor allows tile or stone to be laid over the top, bonding it to the subfloor. Thick-bed mortar is applied over the subfloor and allowed to dry before laying tile or stone, creating a “floating” mortar that can move independently of the subfloor, to avoid cracking tile if the subfloor shifts.
    SLC sets up quickly. For small jobs, SLC can be mixed by hand or mounted to a power drill over a bucket. Larger jobs can be completed with two or three people mixing and pouring enough concrete for an area and allowing the concrete to set up before mixing another batch and moving on to the next one. A pump can also be used for larger jobs where mixing isn’t practical.

Why should I use SLC with my heating project?

Besides protecting electric radiant heating wires and mats, SLC/SLUs smooth out subfloors and eliminate irregularities for an optimally even surface before laying any flooring type.

SLC/SLUs also strengthen floors and are preferable to backer board or plywood, which can flex and bend. Unlike plywood and many backer boards, SLC/SLUs also create a moisture barrier to prevent water from seeping into the subfloor where it can grow mildew and rot.

Which floor heating projects require SLC/SLUs?

Besides the added benefits mentioned above, many products Warm Your Floor sells require self-leveler used as an underlayment to encase the electric radiant heating elements to protect them from the flooring. For glue-down and floating engineered hardwood floors, or floating laminate floors, cover Nuheat and SunTouch wires and mats with SLU first.

For concrete basement floors, lay SunTouch mats or WarmWire cable on top of the slab, then apply a layer of SLC with a tint or your preferred decorative finish to encase them.

Before a self-leveler pour
After self-leveler is poured

2 thoughts on “SLC: Everything You Need to Know for Your Floor-Heating Project”

    I am redoing my bathroom in my basement. It already has tiles on the floor. Was thinking about tiling over the tiles(solid base). Can I Place your mat over the tiles cover with thin set then retile.
    Also do I require an indepedant 15 amp breaker for your unit
    Bathroom is 36” x 58”

    • Hi Rick,

      That is totally fine to place a mat over the existing tile. We recommend using a self-leveler before placing the mat in order to make sure that the floor is completely level. After that, you may place the heating mat and then thinset over the top before placing the new tile.

      As for the wiring, the floor heating systems require a dedicated circuit to a 20amp breaker. The thermostat maxes out at 15amps, so it is important to have the 20amp breaker.

      Please, feel free to contact us at 866-558-3369 if you have any further questions!

      Warm Regards,
      Warm Your Floor Team

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