Can you install microcement over underfloor heating?

Yes, microcement can be applied over underfloor heating. It cannot simply be trowelled over a heated floor with the system switched straight back on, though. Heating changes the temperature of the substrate, and a specific protocol is needed to help prevent the cracks those changes can cause.

This guide sets out the protocol step by step, explains why each step matters and covers how to look after a heated microcement floor once it is finished.

Why heated floors need a protocol

A new cement mortar or screed keeps drying and setting for weeks after it is laid. When heating is introduced, the base expands as it warms and contracts as it cools. If that early movement happens after the microcement has been applied, the stress can show up as cracks in the finish.

At around 2–3 mm, microcement follows the base beneath it. It is flexible enough to cope with minor movement, but not with a base that is still settling or being heated for the first time.

The protocol brings the base through its first heating cycle before microcement goes on, so the substrate is well set, stable and cool when application begins. It adds time to the schedule, but it helps protect the finish.

The underfloor heating protocol, step by step

These steps apply to heated floors with a cement mortar or similar base layer. The temperatures refer to the water entering the heating circuit, so review them with your heating installer.

1. Wait at least four weeks. Turn the heating on no sooner than four weeks after laying the cement mortar or other base layer.
2. Warm the floor gradually. Keep the circuit inlet water at about 25°C for 2–3 days, then increase it gradually to 45°C and hold that temperature for a few days.
3. Switch off and cool down. Turn the heating off at least 48 hours before microcement installation. The maximum floor temperature should be about 18°C.
4. Apply to a well-set substrate. Microcement goes onto a cementitious mortar or other suitable substrate that has reached an advanced setting stage, typically after 3–4 weeks, depending on the weather.

The sequence at a glance

Living with a heated microcement floor

The protocol prepares the floor, but a few ongoing habits keep it performing well once the finish is in place.

Change temperatures gradually

Always bring the temperature up gradually at the start of a heating period and down gradually at the end. Sudden swings from cold to hot, or hot to cold, put unnecessary stress on the floor. Some controllers can be set to change temperature in gradual steps, which is worth discussing with your heating installer.

Avoid very low humidity

Very low relative humidity should be avoided in heated rooms, particularly when the heating runs for long periods through winter. Keep an eye on the conditions in the room as well as the floor temperature.

Prevent heat build-up

Rugs, carpets and furniture that sits low to the floor can trap heat beneath them. Choose furniture with enough space underneath for air to circulate, and think carefully before covering large heated areas with thick rugs. Pieces with solid bases that sit flat on the floor, such as some storage units and platform beds, deserve particular thought.

Allow for an expansion joint

An expansion joint is required between the screed and vertical walls so the screed can expand as it warms. It is typically formed when the screed is laid, so confirm it with your builder or heating installer at the design stage.

Why cracks happen when steps are skipped

Microcement is designed to be durable and flexible, but it follows the substrate beneath it. Cracks over a heated floor typically trace back to one of these issues:

• Heating the base too early, before at least four weeks have passed since it was laid
• Skipping the initial heating cycle, so the base moves for the first time after the finish is applied
• Applying microcement to a floor that is still warm, or before the heating has been off for 48 hours
• Rapid temperature changes at the start or end of a heating period
• No expansion joint between the screed and the walls
• Heat trapped under rugs, carpets or low furniture

Our guide to whether microcement cracks covers other causes, including substrate movement and building shifts.

Existing heated floors

If you are renovating a room that already has underfloor heating, the base will usually be long set, but the same care applies at installation. The heating should be off for at least 48 hours beforehand, with the floor at about 18°C or less, and brought back on gradually afterwards.

The existing surface, whether tiles or a screed, still needs to be stable, level, clean and below 5% humidity. Tell us about the heating when you first get in touch, so it can be factored into the assessment and the schedule.

Planning a heated floor project

Underfloor heating adds lead time to a microcement project, so plan the sequence early:

• Confirm the heating type, the base layer and when the screed will be laid
• Build the heating cycle and the 48-hour cool-down into the schedule
• Check that an expansion joint has been allowed between the screed and walls
• Confirm on site that the substrate is stable, level, clean and below 5% humidity
• Choose rugs and furniture with heat build-up in mind

Agree early who is responsible for each step. Typically the heating installer commissions and runs the system, the builder or screed installer lays the base and forms the expansion joint, and the microcement is applied once the floor is ready. Keep a simple record of dates and temperatures as the heating cycle is completed.

Once the protocol is complete, application typically takes 5–7 days depending on the size and complexity of the floor. See how long microcement takes for the full timeline, and our application process for what happens at each stage.

After the microcement is applied

The microcement keeps hardening and gaining strength over several weeks, so take care with the floor during the first week. When the heating goes back on, bring it up gradually rather than straight to full temperature, and check the timing with us first.

Day-to-day care is the same as for any microcement floor: a pH-neutral cleaner, felt pads under furniture and a sealer that is maintained over time.

A heated, continuous microcement floor can run through living rooms, bathrooms and open-plan spaces without a change of material. Explore more ideas for microcement floors.