Tiling over existing tiles: conditions, preparation and limits

When new tiles can go over old ones

Before suggesting bonding new tiles onto old ones, we check five points. If one of them fails, removal or heavier preparation is needed:

• bond: no tile should sound hollow or move;
• flatness, compatible with the size of the new tiles;
• stability: no crack running across several tiles, a sign that the substrate is moving;
• the height available under doors, at thresholds and on the stairs;
• the load the floor can carry, especially if it is timber.

These are the requirements of any floor and wall tiling job. We treat old tiles as a substrate in their own right, prepared as the primer and adhesive data sheets require, as explained in our article on tiling rules and standards.

The assessment: tap, measure, look

The first check is the tap test: we tap each tile with a mallet, and a hollow sound reveals a loss of bond, even if the tile does not move yet. On a floor, a hollow tile eventually cracks the covering laid on top of it.

We then check flatness with a 2 m straightedge and look for edges that stand proud (lippage), recessed joints and cracks. The type of covering matters too: glazed porcelain, ceramic wall tiles or waxed terracotta are not prepared in the same way.

Preparing the old tiles before bonding

Glazed tiles are a closed substrate: they absorb nothing, so the adhesive only grips a perfectly prepared surface:

• re-fixing defective tiles and filling any holes;
• thorough degreasing and rinsing: in kitchens and bathrooms alike, grease, limescale and soap build up right into the joints;
• light sanding of the glaze if the primer or adhesive manufacturer requires it;
• vacuuming, then a bonding primer for non-porous substrates, respecting its drying time.

The adhesive’s data sheet must list old tiles as an approved substrate. It is usually an improved cement-based adhesive of class C2, often deformable (S1), with back-buttering where the tile size or the room requires it.

Levelling compound over tiles: when is it needed?

A levelling compound is not always necessary: on flat tiles with shallow joints, the adhesive absorbs small variations. It becomes useful if flatness does not suit the new tile size, if the joints are wide and recessed, or if the new tiles are sensitive to the slightest relief, such as large formats or thin porcelain.

Over tiles, it needs a primer made for closed substrates, a product whose classification suits the room and a thickness within the manufacturer’s limits. This work is part of our screed and levelling service, and its cost is covered in our guide to screed and levelling prices.

Extra height: doors, thresholds and fittings

The new tiles add their own thickness, plus that of the adhesive and any levelling compound: usually in the order of one to two centimetres with standard floor tiles. Yet a few millimetres are enough to jam a door. At the visit, we note:

• interior doors, to be trimmed at the bottom while keeping the air gap the ventilation needs;
• junctions with adjoining rooms, finished with a threshold strip or a transition profile;
• the front door or French window, whose frame is hard to alter;
• the stairs, where the first or last step changes height;
• in a kitchen, the integrated dishwasher, which must still fit under the worktop;
• in a bathroom, the toilet and shower tray, to be reset to the right height.

Old skirting is removed and replaced with skirting that matches the new tiles, keeping the perimeter gap along the walls.

On a timber floor or parquet: stiffness and weight

If the old tiles sit on a timber floor, or if parquet is to be tiled, stiffness becomes the key issue: the floor must not flex underfoot, and the boards must be securely fixed, dry and ventilated underneath. A floating floor, laminate or carpet is never a substrate for tiles: it has to come up.

On a rigid floor, tiles are laid on an uncoupling membrane, on a fibre-reinforced levelling compound designed for timber or on suitable boards screwed to the floor, depending on the substrate and the system chosen.

Weight matters too. On a concrete slab it is rarely an issue; on an old upstairs floor, with large formats or stone, we sometimes ask a structural professional for advice. In a flat, in Paris or elsewhere, check with the managing agent as well: some co-ownership rules require acoustic insulation under hard floors.

Wall tiles over wall tiles

On walls the logic is the same: the old tiles are tapped, degreased, descaled and primed before an adhesive suited to the substrate and to the weight of the new tiles is applied. Plan ahead for:

• extending electrical boxes so that sockets and switches stay flush;
• wall-mounted tap connections, which may need extension pieces;
• finishing the edges and window reveals with a trim or a neat cut;
• the extra weight on a lightweight partition or plasterboard.

In a shower, we often prefer to remove the old tiles: if water has got behind them, covering them would trap the moisture, whereas removal lets us check the wall and create continuous waterproofing under the tiles.

When is it better to remove the old tiles?

Tiling over is not always the cheapest option in the long run. We recommend removal when:

• many tiles sound hollow or are cracked;
• the tiles already cover an earlier floor: we avoid stacking layers;
• there is no height to spare, for example to stay level with an adjoining room;
• the timber floor lacks stiffness or cannot carry the load;
• water has got underneath, or the project includes a level-access shower with a recessed drain;
• underfloor heating is to be built into a new screed.

Removal has its own constraints: noise, dust, rubble and sometimes a screed to repair. Whether in a house in the Eure or a flat in Île-de-France, we decide after the visit, and the quote lists removal, preparation and laying separately, as our article on preparing a tiling quote explains.

Frequently asked questions