Screed heating before flooring installation

Functional heating and drying are different tasks

Functional heating checks the operation of a heated floor construction. Drying heating helps bring a screed to the moisture condition needed for a floor covering. Completing the first does not necessarily achieve the second; Uponor distinguishes these purposes in its planning guidance [1]. A heating cycle may reveal cracks or installation problems, but cannot guarantee that every defect will emerge. It also does not replace a required heating-system pressure test.

When can heating begin?

Only after the curing period specified for the screed. Cement, calcium sulphate and fast-setting mixes may require different procedures. Obtain the product name, installation date, screed thickness and heating documentation before deciding when to start or what maximum temperature to use.

Do not copy another project’s heating schedule. Starting too early or increasing the temperature too quickly can conflict with the mix requirements. The screed contractor and heating installer should agree a procedure suitable for the actual construction.

A practical sequence

1. Identify the construction. Collect the screed specification, heating documents and movement-joint plan.
2. Complete curing and the required system checks. Only then start the specified cycle.
3. Follow and record the programme. Note dates, temperatures, interruptions and defects. Arrange moisture removal appropriate to site conditions.
4. Stabilise conditions for testing and installation. A hot screed is not automatically suitable for bonding.
5. Test moisture and assess the substrate. If requirements are not met, agree further drying and retesting.
6. Prepare and install. Restart heating according to the flooring instructions and the adhesive’s curing requirements.

Does the 27°C limit apply to screed heating?

The finished-floor surface limit and a bare-screed heating programme describe different stages. For example, Kährs specifies a maximum surface temperature of 27°C for its wood flooring on underfloor heating [2]. This is neither a universal water setting nor the maximum temperature for heating an uncovered screed.

Keep flow-water, surface and room temperatures clearly labelled in the record. They cannot be substituted for one another.

Electronic measurements and the carbide test

A non-destructive meter helps compare locations and identify areas needing investigation. Its scale, suitable substrates and limitations must be understood. A percentage display is not necessarily CM%. Tramex describes material-specific quantitative scales, comparative readings and carbide-equivalent readings [3]. An equivalent reading is not an actual carbide test.

Acceptance testing must use the method required by the selected system. If CM testing is specified, a representative sample must be collected and tested using the proper procedure. In-situ relative humidity and electronic percentage readings are not automatically interchangeable with CM%.

On a heated screed, use a designated safe sampling point without heating pipes [1]. Do not assume pipes are deep enough to avoid. If sampling points are missing, establish the installation layout before disturbing the substrate.

What moisture content is acceptable?

There is no single threshold for every floor. As a specific example, Barlinek’s guidance for engineered wood on heating gives maximum values of 1.8 CM% for cement screeds and 0.3 CM% for calcium sulphate screeds [4]. Those are product-system requirements, not universal permission to install all wood floors at those readings.

Check screed, levelling compound, primer, adhesive and flooring requirements together. Conflicting instructions need a system compatibility clarification, not a choice of the easiest limit. A moisture-control coating is not a universal alternative to drying.

What else needs checking?

• Flatness, strength and surface cohesion.
• Cracks, movement joints and their continuation through the finished system.
• Contamination and layers requiring removal.
• Subfloor temperature, air temperature and relative humidity.
• Compatibility of preparation products, adhesive and covering.

Record the test result, method, location, date, substrate type, room conditions and decision about further work. Keep heating and moisture records separately.

Common questions

Can heating be skipped in summer?

Warm weather does not replace a required procedure for a heated screed. Documentation and substrate condition determine the scope.

Is waiting several weeks enough?

Time alone cannot establish readiness. Moisture and all other installation conditions must meet the requirements.

Does SPC need a dry screed too?

Yes. A water-resistant plank does not permit installation over an arbitrarily damp substrate. SPC also has substrate and commissioning requirements.