Concrete slabs with underfloor heating (UFH) must be cured properly to avoid cracking, warping, or system failure. Rapid drying, thermal stress, or poor moisture control during early curing can lead to major problems, especially in polished or exposed floors. This guide explains how to cure a UFH slab correctly, maintain surface integrity, and bring the heating system online without damage.
Begin curing immediately after the slab is finished. Apply curing blankets, plastic sheeting, or liquid membrane to retain moisture. The first 48 hours are critical, surface moisture loss during this phase is the number one cause of shrinkage cracking. Avoid airflow from open doors or windows, especially in warm or dry weather. Maintain uniform temperature and humidity around the slab to prevent edge curling and surface tension.
Do not activate underfloor heating during the first 28 days. The concrete must reach sufficient strength and moisture balance before any internal heating is applied. Turning the system on too soon risks thermal shock, internal cracking, and delamination. If temperatures drop below freezing, insulate the area with blankets or passive heating, never use the embedded heating pipes during early cure.
Allow the full 28-day curing window before applying finishes or bringing the system online. During this time, maintain curing sheets, wet coverings, or approved curing compounds. If polishing is planned, remove membrane-based sealers before grinding. Do not remove protective layers early, even if the surface appears dry, internal moisture loss is still ongoing and affects slab strength and integrity.
Movement joints should be cut within the first 24 to 72 hours, depending on ambient temperature and mix design. These joints relieve internal tension and prevent uncontrolled cracking. Use a saw with depth control to cut no less than one-quarter of the total slab thickness. Position joints away from UFH pipes, always confirm the pipe layout before cutting to avoid damage.
After 28 days, begin warming the slab by turning the heating system on at a low temperature (e.g. 20°C). Hold for 24–48 hours, then increase by 2–3°C per day until reaching normal operating range. This controlled ramp-up allows the slab to adapt thermally and prevents microcracks from sudden expansion. Rapid heating can result in fine surface cracks or slab curling, especially on thin or highly finished floors.
Do not install surface finishes (tiles, polish, coatings) before the slab is cured. Adhesion failures, bubbling, and moisture traps are common when coverings are laid too early. Always check the slab’s residual moisture with a hygrometer or moisture test before applying any floor finish. For polished concrete, schedule grinding and sealing after the 28-day window, with heating still off during polishing.
During curing, avoid concentrated loads or heavy traffic. Scaffolding, wheelbarrows, and equipment can create stress points in green concrete. Use plywood sheeting or soft matting to distribute load if access is required. Even when the surface looks set, the internal structure is still gaining strength, small cracks from early impact can worsen when the heating system is activated.
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