Polished concrete over underfloor heating combines aesthetics with efficient heat delivery, but the polishing process must be handled carefully. Grinding too soon, applying excessive heat, or damaging pipes during finishing can undermine the system and compromise the surface. This guide explains how to polish a concrete floor that contains UFH, from curing to sealing, while protecting both the heating system and the structural integrity of the slab.
Curing is non-negotiable. Wait a minimum of 28 days before any grinding begins. This allows the slab to reach sufficient hardness and strength. During this time, keep the slab moist using curing blankets, plastic sheeting, or sprayed compounds. Avoid switching on the UFH system until the slab is fully cured. Premature heating or grinding can lead to surface stress, laitance, or thermal cracking.
Decide what type of polished finish is required. Options include cream polish (minimal grinding), salt-and-pepper (light grind), or full aggregate exposure (heavy grind). For slabs with UFH, deep grinding should be carefully assessed to avoid reducing concrete cover above pipes. You should know exactly how much concrete sits above the UFH zones, and mark any critical areas before work begins.
Perform Mohs hardness testing or surface scratch tests to confirm the slab is ready for grinding. Areas that are still weak or dusty may indicate improper curing or high water content. Polishing over soft concrete will create patchy sheen and uneven clarity. If needed, apply a densifier after the initial grind to harden the surface before progressing through finer grits.
Start with a heavy planetary grinder and a 30 or 50 grit metal-bond diamond. Remove surface laitance and level minor imperfections. Use a cross-hatch grinding pattern and avoid staying in one area too long, especially over known UFH zones. Maintain a slow, consistent pass rate and use adequate water to cool both the slab and tooling, reducing heat transfer into the concrete mass.
After initial grinding, apply a lithium-silicate densifier to harden the surface. Use a sprayer for even distribution and let it soak in without pooling. Densifier helps improve abrasion resistance and reduces future dusting. For heated slabs, ensure the UFH system is off and the slab is cool to prevent rapid drying or poor absorption. Wait the manufacturer’s recommended dwell time before continuing with finer grits.
Move up through the grit levels in stages: 100, 200, 400, and up to 800 or 1500 depending on the desired gloss. Each pass should refine the previous one, removing scratch marks and increasing clarity. Use resin-bond pads with water or densifier reactivation. Watch for overheating — polishing can build surface heat quickly, especially on large slabs. Stop and cool the surface if the concrete becomes warm to the touch.
Use handheld or smaller edging machines to polish around walls, columns, and fixtures. Edges often contain more trowel marks or laitance and may need extra passes. Be especially cautious around manifold zones or wall penetrations. Never use heavy tooling near pipe inlets or visible floor penetrations without confirming depth. These are the most common points of accidental damage during edge polishing.
Once polishing is complete, apply a breathable concrete sealer designed for high-temperature environments. Avoid topical coatings that trap moisture, especially over UFH systems. Use penetrating sealers for long-term protection against stains and wear. Apply in thin coats and allow proper drying between applications. For domestic or commercial use, consider anti-slip additives if required.
Do not activate the underfloor heating system immediately after polishing. Wait several days post-seal to allow curing, then switch the system on at a low temperature. Increase the temperature gradually over 7 to 10 days. Sudden heat changes can crack the slab or weaken sealer adhesion. This ramp-up method ensures long-term stability for both floor performance and finish retention.
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