Heat
Marble and granite conduct heat about ten times better than oak, so the warmth gets through quickly and the stone stores it. The room stays at an even temperature.
Thickness
Floor tiles are usually 1 to 2 cm, large slabs often 2 cm. Thin stone warms faster, thick stone holds the heat longer. For a holiday home heated only when you arrive, go thin. For a house lived in all year, the extra mass helps.
28 °C
In living areas the floor surface is capped at 28 °C in France. That also keeps the stone's movement small. The heating installer sets the water temperature to match.
The screed
The screed has to be cured and dry to the level the adhesive maker asks for. With pipes in it, the heating normally goes through a first cycle before we lay, slowly up to temperature and back down. That drives out moisture and shows any cracks before the stone goes on. The protocol comes from the screed and heating makers, and laying follows DTU 52.2.
Adhesive and joints
- We use a flexible cement adhesive, the bag will say C2 S1.
- Full bed, buttering the back of each tile, so there are no gaps. Gaps make hot and cold spots.
- Movement joints at doorways, round the edges and at set intervals, so the floor can expand.
- White adhesive under white marble, grey can show through.
Tricky stones
Some green marbles curl or stain with water-based adhesive and are laid with epoxy or polyurethane instead. Very porous travertine or limestone can show dark patches for a while as they take up moisture. Ask about your particular stone before laying.
Finish
Honed marble feels warmer and grips better than polished, and shows less wear in a hallway. Polished suits a quiet living room. In a bathroom, honed or brushed is safer when wet. A thick rug stops the heat coming up where it lies.
The first winter
After laying, the heating stays off or low until the adhesive and grout have cured, then goes up in small steps over several days. If a new stone floor is heated up in one go, tiles can crack. In a second home, set this up with the installer before you leave, so the house isn't put on full on your next visit.
Electric mats
For a single bathroom, a thin electric mat in the adhesive bed is common. It goes into the adhesive bed, so you don't need a new screed. Same rules on adhesive, joints and slow first heating.
Existing floors
A dull marble floor over heating can be honed and repolished like any other. Turn the heating down first, wet honing on a hot floor dries too fast. See restoration.
Bring your installer's floor build-up to the workshop at 8 rue Joseph Marie Jacquard, the stone thickness has to fit it. Galala and granite both work well here. See also bathrooms and the farmhouse guide, or call +33 7 45 20 76 39.
