Short answer: usually, yes - and it is one of the strongest reasons clients choose microcement for renovations. Overlaying existing tiles avoids days of demolition, skip hire, dust through the house and the risk of disturbing whatever the tiles were hiding. But "over tiles" is only a good idea when the preparation is done properly, so here is what that actually involves.
First, we interrogate the tiles
Microcement is only as stable as what it is bonded to. Before we quote for an overlay we check three things: that the tiles are soundly bonded (we tap-test the field and lift anything hollow), that the substrate behind them is dry and stable and that the floor level can accept 3-4 mm of build plus any levelling. One or two loose tiles are re-fixed; widespread hollowness means the tiles come up after all - overlaying a failing surface just buys a more expensive failure later.
What a tap test actually is
Not a formality. We go over the entire field with a knuckle or a light mallet, listening. A tile bedded properly gives a dull, dead note. A tile with a void behind it rings hollow - "drummy" - and that void is a bond that has already partly failed. Nothing applied on top will re-attach it.
We mark the drummy tiles as we go, then count them. A handful, isolated and we lift and re-bed those. Clusters, or more than roughly one in ten and the honest answer is that the floor comes up.
The height check
Measured, not estimated. The overlay adds 3-4 mm plus any levelling needed to correct lippage between tiles. We check door undercuts, thresholds, the underside of any level-access shower former and where the floor meets carpet or timber in the next room. Almost always it is fine - that is the whole point of a 3 mm finish - but it is worth five minutes with a tape rather than a conversation on the day.
The moisture check
Tiles are not vapour-open, so a substrate underneath them can hold moisture for a very long time without anyone noticing. If there is any history of a leak, a bathroom below, or a solid floor with no evidence of a DPM, we take readings before we agree to build on it. Sealing moisture in under another impermeable layer does not make it go away.
The overlay build-up
- Degrease and abrade. Glazed surfaces are mechanically keyed so the primer has something to grip.
- Bonding primer. A grip coat formulated for low-porosity surfaces like porcelain and glass.
- Base coats with mesh. Fibre mesh bridges every grout line - this is the step that stops joints telegraphing through as ghost lines months later.
- Finish coats and seal. The same fine coats, compression and sealing as any other microcement installation.
In wet areas we add a waterproofing membrane over the prepared tiles before the base coats, so the enclosure is waterproofed as one continuous system regardless of what is underneath.
Ghosting - the failure people actually see
The characteristic failure of a badly executed overlay is not a crack or a debond. It is a faint grid appearing on the surface some months later, as the grout lines telegraph through the finish and catch the light. Once it appears there is no fixing it short of re-doing the surface.
It happens for two reasons and both are preventable. Either the grout lines were not filled and levelled before the base coats, so the finish is marginally thinner over each joint and cures differently; or the mesh was omitted or laid without proper embedment, so there is nothing distributing stress across the joint lines. Deep or wide grout lines - anything much over 3 mm - need filling as a separate operation rather than being absorbed into the base coat.
If you are comparing quotes, ask specifically how the grout lines will be treated and whether mesh is included. It is the cheapest step to leave out and the most expensive to have left out.
Walls and the harder case of splashbacks
Tiled walls overlay well and the same rules apply, with one addition: tile edges and trims at the top of a half-tiled wall create a step that has to be feathered or removed. A microcement finish running from tiled area onto bare plaster above will show that transition unless it is dealt with and the neatest answer is usually to take the trim off and level across.
What it means for your programme
A typical tiled bathroom overlay saves one to two days of strip-out plus making-good and spares the household most of the dust. Total build-up stays within a few millimetres, so doors usually don't need trimming and thresholds stay level - worth checking at survey and we do.
The cost saving is real but modest - you are saving demolition labour and a skip, not the finish itself. The disruption saving is the larger one and in an occupied house with a single bathroom it is usually what decides it.
When we say no
- Hollow or drummy tiling across large areas - the bond below is already failing.
- Active movement or cracking in the substrate - mesh hides nothing forever.
- Persistent damp behind the existing finish - the cause gets fixed first, always.
- A timber floor that deflects underfoot. If you can feel it move, a 3 mm rigid finish will crack, tiles or no tiles.
- Very large-format tiles with wide, deep joints on a floor, where the levelling required starts to cost more than lifting them.
Roughly four out of five tiled bathrooms we survey are good candidates for an overlay. The fifth is not and we would much rather say so at survey than take the job and be back in eighteen months.
How to find out about your room
Photographs get us most of the way: the whole room, a close-up of the grout lines and anything that looks damaged or damp. Then tap a few tiles yourself and tell us whether any sound hollow - you will hear the difference immediately once you know what you are listening for. Send them over and we will give you a straight answer, including if the answer is that the tiles need to come up.