Can polyurea be applied over existing pool tiles or mosaic?

The most important check is sounding the tiles. With a light hammer or a wooden handle we work systematically across the floor, the walls, the corners and the steps. Where the sound is dull and solid, the tile is still bonded. Where it rings hollow, the adhesive bed has released or the tile has come away from the concrete, even when nothing shows on the surface.

We also look for loose mosaic, which is fixed in sheets and can lift as a whole, for washed out or soft grout, for cracks running through the tiling into the shell, and for moisture pushing through from behind: damp patches, lime bloom, or tiles still feeling wet after days of standing empty. Finally the edges and penetrations, from waterline and skimmer to main drain, lights and overflow channel, because almost every leak starts there.

We do not use a fixed percentage of hollow sounding tiling above which the answer is automatically no. Such a threshold creates false certainty, because the cause tells you more than the count. A few loose tiles on an otherwise healthy shell are local repair work. If the sound is hollow across large stretches, or whole mosaic sheets lift away, the adhesive bed or the substrate is failing. Location counts too: loose tiling at the waterline or around penetrations weighs far more than a patch on a quiet wall.

The pool is first cleaned and degreased thoroughly. We then cut out the hollow sounding areas and make them good locally. Where needed a levelling layer of cement based mortar is applied, around 15 kilos per square metre for a layer of one centimetre. Grout lines and irregularities are filled, otherwise the tile pattern telegraphs through the finish. Glazed or slippery tiling is mechanically roughened.

Next comes the bonding primer rated for permanent immersion, in two coats totalling around 500 grams per square metre, which doubles as a vapour barrier. The polyurea membrane is then sprayed at roughly 2 kilos per square metre, to a final thickness of at least 2 millimetres, seamless and in one continuous pass. The visible finish is a UV and wear layer, rolled on in two coats totalling around 400 grams per square metre. It is the only layer that withstands permanent immersion. The pool may be filled after seven days, not sooner.

No tiles and no adhesive bed have to come off the shell. That saves days of breaking out, rubble, skips and trips to the tip, and it spares the concrete, because every round of demolition occasionally creates damage that was not there before. The pool also keeps its dimensions: step heights, depths and the connections to coping and overflow stay exactly as they were.

It saves time as well. A complete pool renovation takes five to ten working days on average, and overcoating sits at the short end of that range. Spraying itself is a day's work; the preparation takes most of the time. Dates we give remain target dates, because the weather can shift the planning.

The classic mistake is coating over tiles that later let go anyway: the coating bonds perfectly to the tile, but the tile does not hold on to the concrete, and the whole package lifts as one. Just as wrong is coating over moisture trapped behind the tiling with no way out. Residual damp or a substrate that has not fully cured brings osmosis and blistering, sometimes weeks after filling. Things also fail with a missing or unsuitable primer, and on a smooth, plain finish unfilled joints telegraph through as a fine grid.

None of these points are guarantee exclusions by accident: residual moisture or osmosis from an insufficiently cured substrate, a missing or unsuitable primer where a third party prepared the substrate, moisture or water pressure from outside, and work carried out against our written advice. If someone else prepares the substrate, we cannot vouch for what sits beneath our layer. Where we do the work ourselves, the cover is ten years on watertightness, ten years on adhesion, five years on the UV colour stability of the topcoat and three years on the finishing details, counted from the handover date.

Owners who want to keep the look of tiling or mosaic yet still have a closed waterproof skin can turn it around: the membrane goes on the bare shell first, and the new tiling on top of it. The waterproofing then sits under the tiles, and the tiles are a finish rather than the barrier holding the water. A hairline crack or a washed out joint no longer causes a leak. It does call for a different build up and an adhesive suited to the surface, and for more work and a longer lead time than plain overcoating.

The visible finish is the UV and wear layer. Virtually all RAL colours are possible and the pigment runs through that layer, so the colour is not a thin film sitting on the surface.

How flat the result reads is decided by the levelling. Fill only the joints and the old grid stays faintly visible in raking light. Want a completely even surface, and more levelling work is needed, which costs time in the preparation rather than in the spraying. Where anti slip is wanted it can be blended into the topcoat, usually on the steps, in the shallow end and along the walking edge.

If the tiling is loose over large areas, or whole mosaic sheets are leaving the wall, stripping back to the shell is the honest choice. A new layer over a loose substrate is postponement, not a solution. The same applies to moisture or water pressure from outside, for instance a high water table or a leaking pipe behind the shell: we resolve that cause first, because a coating does nothing against it and it falls outside the guarantee.

A shell that is still settling or is structurally unsound must come to rest or be repaired first, because movement beyond the elongation limit of the system is likewise excluded. And if the pool is going to be replaced, enlarged or reshaped before long, wait until the shape is final and then do it properly in one go.

Whether overcoating is sound in your case depends on what is happening under the tiles, and that shows fastest on site. We come and look free of charge, and we can judge from photographs as well: an overview of floor and walls, close ups of the waterline, the steps and the penetrations, plus every spot where you notice something yourself. After that you hear what we found and which approach goes with it, with a quotation within 24 hours.