Microcement floors in Mallorca

The floor is where microcement works hardest: it takes footsteps, chairs, sand from outside and the water from mopping. That is why a microcement floor is not only a question of colour and finish; it is a question of what is underneath and how it is protected on top. On this page we explain how it is applied over tiles and over screed, what happens to the joints, how thick it is, which sealers are used, how it wears and how it is cleaned, and what happens when there is underfloor heating.

Microcement floors over tiles and over screed

Over tiles or terrazzo, the work starts by checking that every piece is firm. Those that sound hollow are removed and the gap is filled with repair mortar. The joints between tiles are filled with a levelling paste until the surface is continuous; skip this step and the grid of the tiles reappears through the microcement as soon as the material dries and shrinks. The glaze is then sanded to open the surface, and a bonding primer for non absorbent substrates is applied.

Over cement screed or concrete, the process changes. The substrate must be cured, dry and free of surface laitance. A new screed needs at least four weeks; if it is covered sooner, the moisture still coming out of it lifts the sealer. Cracks are opened, sealed with resin and bridged with mesh; uneven areas are corrected with self-levelling compound before the microcement, because 2 to 3 mm levels nothing. The primer here is a consolidating one, so that the screed does not draw the water out of the first coat.

Expansion joints and cracks

Microcement is continuous, but the substrate is not always. The expansion joints in a slab are there because concrete moves with temperature, and that movement does not disappear because it has been covered over. The rule is to respect them: they are cut into the microcement in the same place and filled with an elastic sealant of the same colour, or marked with a profile. Covering them gives a perfect floor for a few months and a straight crack afterwards.

Shrinkage cracks, the fine ones that do not move, are treated and covered with mesh. Active cracks, the ones that open and close with the seasons, are a sign that the substrate is not suitable. We say so at the visit, even if it means not doing the job.

Thickness and flatness

The complete system adds up to between 2 and 3 mm: two coats of base microcement, which has a coarser grain, and two coats of fine finishing microcement, sanded in between. That thickness does not correct unevenness or undulations: whatever is out of level stays out of level. That is why flatness is dealt with beforehand, with self-levelling compound or a levelling layer, and the microcement only provides the surface. Doors hardly ever need trimming; skirting boards are taken off and refitted, or replaced with a microcement skirting or a recessed profile.

Sealers and finishes

The real protection of the floor is the sealer. The usual system is a sealing primer that closes the pores of the microcement and two coats of two component water-based polyurethane. The sheen is chosen from matt, satin and gloss; matt hides marks better and gloss brings out the watermarking of the colour more. The polyurethane reaches its working hardness after 7 days: until then, no dragging furniture, no mopping with lots of water and no rugs. In busy areas we add a water-based maintenance wax, a sacrificial layer that is renewed without touching the polyurethane.

Wear and cleaning of a microcement floor

Sealed microcement scratches with sand, with metal chair legs without felt pads and with office chair castors. It does not break up, but it marks, and the marks show more on gloss finishes and dark colours. In an entrance that gets a lot of soil, a large doormat and a matt finish are advisable.

Daily cleaning is water and pH neutral soap, with the mop well wrung out. Bleach, ammonia, vinegar, strong degreasers and limescale removers are out, because they attack the polyurethane. Wine, coffee or oil stains should be cleaned promptly; left for hours on a sealer that is already worn, they get into the mortar. A maintenance wax once or twice a year, and renewing the sealer when water stops running off, keep the floor going for many years.

Microcement over underfloor heating

It is compatible, on two conditions. The heating screed must have been through the commissioning protocol, with the temperature raised gradually and then lowered again, so that all the shrinkage happens before it is covered. And the heating is switched off 48 hours before work starts and stays off until a week after sealing; then it is brought back up gradually. Done this way, microcement transmits heat well, because it is thin and mineral, and it does not suffer.