Microcement on Underfloor Heating - How to Do It Right

More and more clients are choosing to forgo traditional radiators in favor of underfloor heating. Although this solution is more expensive to install, it offers better thermal comfort and is cheaper to operate. However, not all finishing materials are suitable for use with underfloor heating. For example, you need to be careful with large floor tiles and many types of wood. But what about microcement on underfloor heating? Microcement can absolutely be used with underfloor heating, but there are a few important rules you need to follow.

1.Take Microcement Thickness into Account When Designing the Screed Height

The microcement system is only 3 mm thick, so it’s important to ensure that the screed is poured at the correct height. This way, the total floor height-including the microcement-will match the floor level in other rooms.

2.Cure the Screed Properly

Underfloor heating systems are typically installed under a cement or anhydrite screed. Once the screed has set, the underfloor heating should be turned on to evaporate moisture from the screed. This process must be carried out slowly—gradually increasing the temperature by 5°C per day until the maximum temperature of 45–50°C is reached. This maximum temperature should be maintained for 4–5 days. After that, gradually decrease the heating by 5°C per day. The entire curing process takes about three weeks. The substrate moisture content should not exceed 4%.

3.Prepare the Expansion Joints

Microcement itself does not require additional expansion joints, but we recommend recreating the expansion joints that exist in the concrete screed to which the microcement will be applied.

 

Below is a post by Artial Design, a microcement contractor from Kraków, showing photos of properly prepared expansion joints before microcement installation. The previous team that poured the concrete floor created too few expansion joints, which caused the concrete to crack. Before starting their work, the specialists from Artial Design had to carefully prepare the existing expansion joints and cracks to make the surface suitable for microcement. They stitched the expansion joints and other cracks in the screed and, after completing their work, cut new expansion joints where needed. Typically, expansion joints are placed at door thresholds or used to “divide” large rooms (over 20 m²) into smaller sections.

4.Use a Fiberglass Mesh Before Applying Microcement

Using a fiberglass mesh helps absorb stresses caused by subsequent heating of the substrate and prevents them from transferring to the microcement layer. The substrate should be sanded and vacuumed, then the first layer of base coat should be applied, with the mesh embedded in it (our reinforcement kits are available in our store). It’s worth investing in a high-quality mesh—cheaper options can unravel. After 3–4 hours, apply a second layer of base coat over the mesh to achieve a smooth surface.

 

After another 3–4 hours, lightly sand the surface, remove any dust, and you can proceed with applying the first layer of microcement.

Once this layer has set, sand it again and apply the final layer of microcement.

During the microcement application process, under no circumstances should you turn on the underfloor heating, as this may cause microcracks on the microcement surface.

5.Apply Two Coats of Sealer

The final step is sealing. On the day after applying microcement, apply two coats of dedicated sealer for microcement. The interval between coats should be at least 12 hours. Why do we recommend one coat of sealer for walls (except in wet rooms) but two for floors? Floors are exposed to heavier wear and damage, so to ensure full protection, we recommend applying two coats. With just one coat, some areas might be inadequately covered; two coats minimize this risk. It’s also worth mentioning that the best microcement sealers are two-component polyurethane sealers (such as PU Fest 2K). They offer optimal durability, water and stain resistance, easy application, do not yellow, and do not leave roller marks.

 

The floor is ready for use after 7 days. Only then should you turn on the underfloor heating.

Frequently Asked Questions:

Can I use microcement with underfloor heating?
Yes.

 

Does microcement create too much thermal resistance?
No. The microcement layer is very thin and microcement itself conducts heat very well.

 

Can microcement be applied over anhydrite screed?
Yes.

 

Does microcement crack due to temperature changes?
No. Thanks to its special polymer blend, microcement is flexible and does not crack, which is why it can be used on underfloor heating, in saunas, or for finishing fireplaces.