Microcement over tiles in Mallorca

The question we are asked most about microcement is whether it can go on top of the tiles that are already there. Almost always, yes. Microcement for tiles is not a different product: it is the same 2 to 3 mm system with a preparation designed for a ceramic substrate that is smooth and full of joints.

Why put microcement over tiles instead of breaking them out

Breaking out a bathroom or a kitchen means days of hammering, rubble carried down the stairs, a skip in the street and then a new substrate and new tiling. In a Palma flat with no lift, getting the rubble down is half the job. Over the existing tiles there is no demolition, the rubble comes down to the few hollow tiles that are removed, and the plumbing stays where it is.

For the household, that means less dust, only the dust from sanding, which is vacuumed up; fewer days, because a complete bathroom takes five to eight calendar days including curing, against the weeks it takes to demolish and retile; and fewer surprises, because nothing behind the tiles is opened up. The room is still out of use while we work: if the house has only one bathroom, it is worth planning for. The saving comes from the work that is not done; we explain it on the page on microcement cost.

What we check before quoting

Microcement is only as good as the tiles underneath, which is why we give a price after seeing them:

• Tapping, tile by tile. We tap every tile on the floor and walls. One that sounds hollow has air behind it and would come away with the microcement on top.
• Cracks and movement. A single broken tile is an impact; several cracked in a line, expansion joints or partition walls that shake when a door closes point to a substrate that moves.
• Damp behind. Dark joints, loose tiles near a pipe or stains on the other side of the wall. We measure the moisture; a leak is repaired first.
• Joints. Their width and depth decide how much levelling paste is needed; tiles with relief need a full skim.
• Type of tile. Glazed tiles, stoneware and porcelain are closed substrates: they are sanded and take a bonding primer. Terracotta and unglazed tiles absorb: we check that they bring no damp or salts with them and use a consolidating primer.

Where the tiles are matters too. On the floor, footsteps and furniture rule, and the mesh and four coats are essential. On walls there is less wear, but old wall tiles often have more hollow pieces than you would expect. On a kitchen splashback, the grease built up behind the hob stops anything bonding and has to be removed thoroughly. Whole kitchens, worktops included, are covered on microcement walls and kitchens.

How the tiles are prepared

Preparation takes almost as long as the microcement, and it is what stops the grid of the joints appearing a few months later.

1. Hollow and broken tiles. They are removed and the gap is filled with repair mortar flush with the rest.
2. Cleaning and degreasing. Soap, grease, old silicone and the limescale left by Mallorca's hard water are all removed. Any residue acts as a release agent.
3. Joint levelling. The joints are filled with levelling paste until the surface is continuous. Skip this step and the microcement shrinks over the joints as it dries and the grid shows through.
4. Sanding the glaze. It opens up a surface made so that nothing sticks to it.
5. Primer. A bonding primer for non absorbent substrates, or a consolidating primer on terracotta and porous tiles.
6. Fibreglass mesh. Embedded in the first base coat, it spreads stresses and bridges the joints between tiles.

Then come two base coats, two finish coats sanded in between, and sealing with a primer and two coats of water-based polyurethane. In the shower, a cementitious waterproofing goes on first, as we explain on microcement bathrooms.

How much height it adds: doors, skirting and shower trays

The system adds 2 to 3 mm, a little more where the joints are very wide or the tiles have relief. It is not much, but we go over every junction:

• Doors. They hardly ever need trimming; we check the ones that already catch.
• Skirting. A tiled skirting can be coated in the same microcement or replaced with a profile; a timber one is taken off and refitted.
• Shower trays. A tiled built-in tray is kept; a ceramic or resin tray is usually replaced with a built-in one laid to a fall.
• Appliances. Under the worktop, an extra 3 mm can leave an integrated dishwasher with barely enough room. We measure and, if needed, the feet are adjusted.
• Walls. Switch and socket plates, tap flanges and accessories come off and go back on over the microcement.
• Thresholds. Where the coated floor meets one that is not touched, there is a step of a few millimetres, finished with a threshold strip.

Tiled floors with underfloor heating

They can take microcement. The heating screed did its shrinking long ago; what we watch is the tiles, because heating and cooling cycles loosen them, so tapping matters even more here. 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. The full protocol is on microcement floors.

Outdoor tiles on a terrace

Over the tiles of a terrace or porch we use an exterior system: a tougher microcement, aliphatic polyurethane with a UV filter and anti-slip aggregate wherever it is walked on wet. First we check the fall towards the drain and locate the expansion joints, which are cut through in the same place. The details are on outdoor microcement and pools.

If the terrace leaks into the room below, microcement will not fix it: it is not a membrane, and putting it on top only hides the problem until the autumn rain. First the terrace is waterproofed, often with a liquid membrane over the same tiles, and the microcement goes on top as the finish.

When microcement over tiles is the wrong answer

There are cases where we will not do it, even when asked:

• Tiles that move. If they sound hollow over large areas, removing the loose ones is not enough: the rest will follow.
• Damp from below. On ground floors laid on soil with no damp-proof membrane, moisture reaches the microcement from behind and blisters the sealer. The same goes for an active leak inside a wall.
• Cracked screed. Cracks running across several tiles in a line show that the substrate moves, and the microcement will copy the crack.
• Flexible substrates. Tiles on timber boards, on a floating floor or on a plasterboard partition that flexes.

What we do then depends on the cause. If the problem is one area, only that area is lifted, the substrate is rebuilt in mortar and, once it has cured, at least four weeks for new screed, the microcement goes on top. If there is damp or a leak, it is solved first and measured again. If the whole substrate moves, we say so plainly: sometimes the sensible thing is to lift and retile, and we compare both in microcement or tiles.