Pool interior finishes: porcelain tile vs plaster

Three families, three different jobs

The interior finish does three things at once. It is the surface you touch, the colour of the water you look at and — in one case out of three — the thing that keeps the water in. That last point decides most of the rest, so start there. A reinforced PVC membrane is waterproofing and finish in one layer; tile and plaster are finishes laid over a shell something else has already made watertight.

So the real choice is between three families. Porcelain and mosaic tile: the most durable, the most expensive, the one that still looks new after twenty winters. Cement-based plaster — marcite, quartz blends, polished aggregate: seamless, affordable, renewable on a rhythm. Reinforced membrane, 1.5 mm PVC welded on site: the pragmatic European default, the fastest route from shell to swim, and replaceable without touching the structure.

One-piece fibreglass pools sit outside this decision: they arrive with their own gelcoat, and the colour you order is the colour you keep.

Water colour comes from the finish

Pool water is very nearly colourless. What you see is the finish, read through one to two metres of water, and the water only deepens it. White interiors give bright turquoise. Sand and cream give a warm lagoon green. Grey cools everything towards steel blue. Deep anthracite and black stop reading as water and behave like a mirror, handing back the sky and the planting around the pool.

Depth is the other half of the equation. The same finish reads two shades lighter over a 15 cm tanning ledge than over a 1.8 m deep end, which is why pools with a generous shallow zone photograph brighter. Judge colour accordingly: ask for a sample of at least 30 × 30 cm, sink it in a bucket of water outdoors, and look at it at midday and again at dusk. A dry sample under showroom light tells you almost nothing.

This is the one decision worth playing with before you commit. Open your own dimensions in the designer, flip through finishes and colours, and look at the pool in day and night light. It is free and takes minutes.

Porcelain tile: the durable premium

Fully vitrified porcelain absorbs almost no water — under 0.5 % — and that single number is why it is frost-proof, colourfast and chemically indifferent to whatever your water is doing. It is the one interior that outlives the plant room around it. It asks the most in return: a sound shell, a substrate skimmed flat, a tiler who has done pools before, and pool-grade epoxy grout throughout.

Format changes the character completely. Mosaic at 2.5–5 cm on mesh sheets wraps curves, radii and Roman steps without a single cut, and forgives a wall that is not quite true. Large formats — 30 × 60 up to 60 × 120 cm — read calm and architectural, but need straight walls and a flat shell; every millimetre of unevenness becomes a lipped edge you find with your foot.

Grout is not a detail. Its colour decides whether you see a surface or a grid: matched to the tile it calms everything, contrasted it draws the pattern and makes a small pool look busy. Pick it on site, wet, next to the actual tile.

The finish is the only part of the pool you look at every day and touch on every swim — and the only one you cannot change without emptying it.

Plaster: the affordable classic, on a rhythm

Plaster is a cement-based layer troweled straight onto the shell: white marcite, harder quartz blends, or polished aggregate with the pebble exposed. It is seamless, takes any free-form shape, and can be renewed without touching the structure. The renewal is the deal you are signing: 10–15 years from a good quartz plaster, less from plain marcite, more from polished aggregate.

Plaster is also the finish most sensitive to your water. Aggressive, low-calcium water etches it. Hard water scales it. A chlorine tablet left lying on the floor bleaches a permanent pale ring. The first month matters more than any other: fresh plaster wants daily brushing and careful chemistry while it cures, and a builder who waves that away is saving his time, not your money.

Feel matters too. Marcite and quartz are smooth underfoot. Polished aggregate is grippy and hard-wearing — excellent on steps, unkind to the knees of a toddler crawling in the shallow end. Touch a sample before you decide; a photograph cannot tell you this.

Reinforced membrane: the pragmatic default

A 1.5 mm reinforced PVC membrane is welded together on site over concrete, blockwork or steel panels. It is waterproofing and finish in one layer, it forgives a substrate that is out by a few millimetres, and it turns a finished shell into a swimmable pool in days rather than weeks. If the budget is the binding constraint, this is where money goes furthest.

The honest limits: the welds are visible, inside corners need a careful installer, and a printed mosaic or stone pattern convinces from the terrace and is obviously a print up close. Life is 10–15 years — longer under a cover with sane chemistry, shorter with high chlorine, heat and unbroken UV on the waterline. Re-lining later is a planned event, not a renovation: drain, strip, weld, refill, swim.

Choose the installer over the brand. The material is broadly similar across serious makers; the difference between a membrane that looks tailored and one that puckers at the corners is the person holding the hot-air gun.

Mix finishes where it pays

The waterline is where a pool gets dirty. Sunscreen, body oils, pollen and calcium collect in the top few centimetres, and it is also the band everyone looks at from the deck. Tiling a 20–25 cm band there — and the steps with it — puts tile exactly where it earns its keep, for a fraction of the price of tiling the whole basin.

It works over plaster and over membrane alike, and it is the most common upgrade on a mid-budget build. Visually the band is a frame: matched to the coping it calms the pool, contrasted it draws a hard line around the water. Get its height right, so the water sits in the middle of the band and the tide mark never lands on plaster.

Grip, where it actually matters

Everything under 50 cm of water gets walked on. Step treads, benches, tanning ledges and the first metre of shallow floor are all places where a wet foot lands with weight behind it, and glossy large-format tile there is genuinely dangerous. A polished 15 cm ledge is a skating rink with an audience.

Ask for the textured or anti-slip version of your tile on every tread, on the ledge and across the shallow floor, and for a rounded nosing piece at the step edge instead of a cut tile. Polished aggregate plaster and embossed anti-slip membrane do the same job. Nobody has ever stood in a pool wishing the steps were more slippery.

The twenty-five year view, and what a builder will ask

Upfront the order is predictable: membrane cheapest, plaster in the middle, tile the most — and with tile, more than half of that is labour, not material. Stretch the view to twenty-five years and it inverts. A membrane pool is re-lined roughly twice in that time, a plastered pool renewed once or twice, a tiled pool simply cleaned. Tile is usually the cheaper expensive option; you just pay for it at the worst possible moment, when the build already cost more than planned.

Whatever you pick, your builder will want the same handful of answers: what the shell is and how it is waterproofed, how flat the substrate can realistically be made, whether the pool stays full through winter, how hard your tap water is, and which format and grout you want. Bring those and the quote stops being a guess.

What goes wrong in practice

1. Choosing colour from a dry sample

   Dry tile under showroom light is a different colour from wet tile under 1.5 m of water and an overcast sky. Sink the sample in a bucket and look at it outside, or judge it in a render of your own pool.

2. Large-format tile on a wavy shell

   Big tiles need a flat substrate; on a shell that is a few millimetres out, every joint becomes a lip you feel underfoot and see in raking light. Either the shell gets skimmed flat first, or the format comes down.

3. Ordinary grout in a pool

   Standard cementitious grout in permanently chlorinated water goes chalky, stains and washes out of the joints. Epoxy or a purpose-made pool grout costs more per bag and saves a full re-grout in year five.

4. A dark pool with no plan for maintenance

   Anthracite and black look extraordinary and show every trace of calcium scale, dust and pollen. Dark finishes want stable water chemistry, a robot that runs often and a cover — otherwise the pool looks dusty a week after cleaning.

5. Treating the first month as ordinary

   New plaster cures underwater, and the chemistry and brushing of those first weeks decide how it looks in year ten. Agree the start-up routine with the builder in writing before the pool is filled.