When properly selected, installed, and maintained, ceramic tiles are one of the most durable of all materials used to finish pools and spas. Certain types of natural stone tiles may be used in these areas, but the stones must have the same properties exhibited by vitreous or impervious ceramic tiles. They must also be strong enough to withstand the normal brushing, chemicals, and maintenance necessary for a pool or spa environment.

Photo 2: The tiles at the waterline, and those attached to the concrete tank, were installed more than 28 days before the plaster work shown here was completed.

As well, tiles installed on the coping or walkways surrounding a pool or spa must not be too slippery. Careful selection should also extend to the adhesives, grouts, and sealants used around pools and spas: as in tiles, some installation materials are preferred and some should be avoided. The main issues are the rate of absorption of all materials used for the installation, the submerged strength of the adhesives and grouts, and the toughness of the surface of the tiles.

Photo 3: Cavities incised into the back of this grip-edge tile improves the bond strength between the tile and the pool’s cast mortar coping.

Tiles

Absorbent, non-vitreous tiles are frequently used in tropical climates, at the waterline, without much concern about freeze-thaw damage, and little thought about mold and mildew. But while non-vitreous tiles may be safe in non-freezing climates, they are porous enough to harbor mold and mildew. For that reason, I install only impervious porcelain tiles at, above, or below the waterline that meet the P1 requirements of ASTM C373 (see Photo 1). If the tiles are unglazed, I have little concern about wear, but if the tiles are glazed porcelain, it is important to select a glaze with a finish strong enough to withstand brushing, chemicals or salts, and the tough cleaning materials and methods that are sometimes required to keep the waterline free of encrusted salts and minerals that occasionally accumulate in pools, spas, and fountains. When tested according to ASTM C1027, Classes III, IV, or V are preferred. Class I or II glazed porcelain tiles are not recommended.

Photo 4: Applicator cleaning plaster residue from the surface of a tile. The tiles and their beds of thinset mortar are a bit less than 1/2-inch – about the thickness of the finishing layer of plaster.

Bond strength is definitely an issue in a wet or submerged environment, and a concern with some types of tile made from metal or glass: glass tiles with a back-coating are particularly difficult to bond under any conditions, and may be impossible to bond in a pool or spa. If glass tiles are desired, I prefer uncoated, face-mounted glass mosaics, and follow ANSI A108.14, A108.15, or A108.16.

Chlorine and salts attack some metals and the resulting oxidation can cause discoloration. For best results when a metal tile is desired, choose stainless steel over brass, copper, or iron. Brass and copper oxides can stain grout blue and iron can turn white grout orange.

Photo 5: Timing is critical for the installation of the plaster, which must be cured by filling the pool: All tiles must be cured a minimum 28 days prior to the day of plastering.

Adhesives

Latex is known for its ability to enhance dry set thinset mortars, however, not all latex or acrylic admixtures are suitable for submerged environments. Under the right conditions, and even after extensive curing, certain latex components can re-emulsify, soften, leech into the surrounding water, and cloud or contaminate it. Generally speaking, latex thinset mortars designed for pool, fountain, or spa use require a 28-day cure prior to immersion (see Photo 2). The same is true for most regular dry set thinset mortars approved for constant immersion.

All tiles installed above, at, or below a pool or spa’s waterline should have minimum 95% adhesive coverage to help eliminate voids and the potential to harbor mold or mildew. Of course, the role of most in-pool tiles is aesthetic, but some pool tiles are designed to enhance the safety of the people using it. The grip edge used to trim the edge of a pool’s coping is an example. To increase adhesion for the fat, 3/4-round grip-edge tiles shown in Photo 1, the manufacturer incised numerous cavities in the porcelain clay body, before firing, to ensure a tenacious grip regardless of what adhesive is used (Photo 3).

Photo 6: This view shows the grip-edge tiles installed, the coping tiles staged to the right, and a movement joint running right up the middle.

Probably more important than the type of thinset mortar you use is the time that must be allowed for whatever thinset mortar is used to cure properly. Curing cannot take place without water, but subjecting many thinsets to total immersion usually results in a reduction of bond, shear, and compressive strength. Under extreme conditions, some thinset mortars can actually re-emulsify when subject to premature immersion. For the installation contractor, timing is a critical factor in all pool, spa, or fountain installations. No tiles should be installed over a concrete tank or base until the concrete has cured a minimum of 28 days, and no tiles, adhesives, or grouts should be subject to total immersion until 28-days after the last tiling material has been installed (Photo 4).

All-tile pools and spas are quite common, and they require a highly detailed network of movement joints that require periodic maintenance and replacement. I prefer to use tiles as accents with plaster as the main finishing material. To do this, I simply wait 28 days for the concrete tank to cure, clean off the surface, install tiles directly over the concrete tank with thinset mortar. And allow them to cure 28 days before plastering up to them. Since the plaster must be immersed completely in water on installation (Photo 5), the timing for curing the tiles is critical to the durability of the pool or spa.

Photo 7: A network of movement joints between the pool and spa and the surrounding stone deck ensures long life for this installation.

Normally, the last job is to install the tiles covering the pool coping. In Photo 6, the grip-edge tiles have all been installed, and the remaining coping tiles have been staged. At the center of the photo is a movement joint between the pool’s tank and the surrounding sloped deck covered with irregular stone. Throughout the year, even in stable tropical climates, a pool will move independently of its surroundings.

When the pool shown in the photos was built, it required approximately 524,000 pounds of concrete; filling it required 48,000 gallons of water or another 400,000 pounds: A pool tends to move, expand, contract, and travel (sometimes) when it wants to and without regard to anything in its way. A half-inch wide movement joint allows the pool to move within reason, prevents damage to the deck stones or coping tiles, and is a requirement for all pools and tiled-in spas (Photo 7).

Resources:

Standard Specifications for tile are available from the Tile Council of North America at: www.tileusa.com

Tiles courtesy: Michelle Griffoul Studios, www.michellegriffoul.com

Photos courtesy: Mike Mesikep