5.1 Considerations for Tile Selection

5.1 Considerations for Tile Selection

Tile and stone in swimming pools, fountains, spas, and water features is a very appealing way to provide beauty and functionality. There are many types of tile and stone in the world, but not all of them are suitable or functional in a submerged installation. Choosing a tile or stone that is suitable for submerged applications is critical to the long-term performance of the installation.

Generally speaking, tile or stone used in submerged installations must have a low absorption rate, a high coefficient of friction, be freeze/thaw resistant (in cool climates), resistant to moisture expansion, and chemical resistant.

Tile used in swimming pools, fountains, spas, and water features should be vitreous (absorption rate between 0.5% and 3%) or impervious (absorption rate less than 0.5%). Absorption rate of tile is determined by ASTM C373 “Standard Test Method for Water Absorption, Bulk Density, Apparent Porosity, and Apparent Specific Gravity of Fired Whiteware Products” and is important for selecting tile or stone for submerged installations, wet areas or any installation that will be subjected to freeze/thaw conditions. Tile for use in submerged installations should also be tested to ASTM C370 “Standard Test Method for Moisture Expansion of Fired Whiteware Products” to determine the extent to which tile will expand when exposed to moisture. Tile or stone with a low absorption rate will be far less susceptible to damage caused by water infiltration and provide a far more durable installation in a demanding environment. The most commonly used tile types for submerged installations are porcelain and glass since they provide the lowest absorption rates. It is also important to check with the distributor or quarry to see if a particular type of stone would be suitable for continual submersion. Ceramic and porcelain tile characteristics are also addressed in the ANSI A137.1 American National Standard Specifications for Ceramic Tile.

Tile with a high coefficient of friction is an important characteristic for tile in continually wet areas, and on pool decks, to help maintain the safety and well being of all who use these areas. Coefficient of friction is commonly determined using ASTM C1028 “Standard Test Method for Determining the Static Coefficient of Friction of Ceramic Tile and Other Like Surfaces by the Horizontal Dynamometer Pull-Meter Method.” Keep in mind that Americans with Disabilities Act (ADA) requires that floor surfaces be stable, firm, and slip-resistant so choosing the correct tile is required to comply with this important Act. Check with local building codes for minimum coefficient of friction values.

Tile in exterior or continually submerged installations must be freeze/thaw resistant, especially in climates prone to this type of exposure. Water can expand up to 25% of its original volume while freezing, and if this water is located within a solid material (e.g. tile, stone, etc…) then a significant amount of damage can occur to the solid material, especially if there are numerous freeze/thaw cycles. Freeze/thaw resistance is measured using ASTM C1026 “Standard Test Method for Measuring the Resistance of Ceramic Tile to Freeze-Thaw Cycling” and establishes the tiles ability to resist freeze/thaw damage.

Due to the amount of chemicals in a swimming pool, fountain or water feature it is necessary to install tile or stone that is resistant to pool chemicals with tile installation materials that are equally chemical resistant. There are several methods for sanitizing pools (including chlorine, bromine, ozone, and salt water) and the tile should be able to withstand whichever sanitizing type will be used in that particular pool. The chemical resistance of tile is established using ASTM C650 “Standard Test Method for Resistance of Ceramic Tile to Chemical Substances”.1

Tile should be UV stable, maintain its color when exposed to various chemicals, easily cleanable, and stated for use in submerged installations by the manufacturer. Choosing the wrong tile can lead to significant down time for the pool, tremendous expense removing the old tile, reinstallation of a suitable tile, and other potential issues that can occur when a pool is empty (see Section 4.5 and Section 11 for more information).

Abrasion resistance, more important on a pool deck tile installation, should also be taken into consideration. Testing for abrasion resistance is performed using a test developed by The Porcelain Enamel Institute (PEI). Tile is tested and given a PEI Rating based on a 0 – 5 scale, as shown in Figure 1.

Figure 5.1 – PEI Rating Chart.1

Tile used in residential swimming pool areas should be PEI 3 or higher and commercial swimming pools should have a rating of PEI 4 or 5. Abrasion from chairs, umbrella stands and other hard materials can scratch the surface of tile and cause damage, so choosing a suitable tile is particularly important.

Failure to properly choose and specify a tile for submerged installations can be a costly, time consuming and unnecessary problem. It is essential to choose wisely! Make sure that not only the tile is suitable for this type of installation, but also the way the tile is mounted (mosaics) and the setting materials used to install the tile as well. Mosaic mounting methods will be covered in Section 5.3 while suitable setting materials are covered in Section 7.

5.2 Placement of Tile in Swimming Pool and Pool Deck Installations

Tile can be installed in almost any area within a pool and the color and design may only be limited by the designer’s imagination. Choosing where tile or stone will be placed is subject to whatever the finished appearance is to be. Tile can be installed within the entire shell of the pool, just on the bottom, just on the walls, at the waterline, on the coping, and, in competition pools, can be used to designate lanes and depths. Tile is often placed at the waterline because floating oils, dirt and waste can combine to form a scum line around the pool; this is why tile, an easily cleanable surface is placed at the water line around the perimeter of pools.2

Figure 5.2 – Tiled lane markers in Water Cube, Beijing, China.

Tile is a very popular finish option for pool decks and choosing a tile or stone for these areas can have a significant visual and safety impact. A pool’s functional performance depends largely on the correct use of slip-resistant materials in the various areas (e.g. pool bottom, steps, deck, etc…). It is extremely important to avoid the risk of accidental falls by using slip-resistant tile, even if it means sacrificing some aesthetic values and easy cleaning. However, floor cleaning is an essential factor to ensure that the tile slip-resistant performance is kept intact.

There are several methods for determining slip-resistance of tile, and the test method used depends upon which governing body is is in place in the country where the installation is done. For years the tile industry in the United States has endorsed ASTM C1028 “Standard Test Method for Determining the Static Coefficient of Friction of Ceramic Tile and Other Like Surfaces by the Horizontal Dynamometer Pull-Meter Method”. While this test method is fine for laboratory conditions there has been a push to use different methods for conducting tests in the field, such as;

1. The variable-angle ramp human traction test method as the primary standard for validation of portable slip-resistance methods;

2. The Tortus dynamic slip resistance measuring instrument, with digital data acquisition, for wet testing, and the use of a trace of Triton X-100 wetting agent in distilled or deionized water as the wetting liquid. The minimum value using this test method for use in bathtubs, showers and pool decks is 0.70; and,

3. The pendulum dynamic slip resistance measuring instrument for wet testing, and the use of the pendulum test guidelines recommended by the United Kingdom Slip Resistance Group. The minimum British Pendulum Number (BPN) on wet, clean flooring is 35 for showers and pool decks.

The Tortus method and the Pendulum method are recommended for testing performed in the field and have achieved wide acceptance. These has also been significant information obtained using these test methods so as to correlate human traction test data with well-simulated mechanical analogs of human traction.3

Germany, Australia, New Zealand, Italy and many other countries have their own standards and test methods for determining both the slip-resistance of tile and acceptable minimum levels to which tile must perform. Whichever test method is employed, the main focus is on providing the best protection for all those who will be using the pool and pool deck.

Another factor which should be taken into consideration for pool deck tile installations is what temperature the finish will be when exposed to direct sunlight. A light colored tile or stone is an ideal choice to absorb less of the heat and maintain a safe and comfortable temperature. Dark colored tile or stone can get extremely hot and create an uncomfortable environment for pool and pool deck users.

5.3 Types of Tile for Submerged Applications

While the types of tile (e.g. impervious, vitreous, some stone, and glass) recommended for use in submerged installations is rather limited, the myriad of colors, sizes, shapes, and designs is very impressive in scope. Tile can range in size from mosaics as small as 3/4" × 3/4" (19 mm × 19 mm) to as large as 4' × 4' (1.2 m × 1.2 m), and stone can come in any size, shape or thickness. Many companies even manufacture pre-fabricated designs in tile which are placed within the finish at the bottom of a pool or fountain and provide a unique and aesthetically pleasing characteristic.

As stated earlier in this section, tile used in submerged installations should have a very low absorption rate (≤3%) which helps to minimize, or even eliminate problems caused by moisture expansion and contraction. Impervious tile and vitreous tile are the most popular choices for swimming pools around the world because they are relatively inexpensive and easy to find. Glass tile, suitable for submerged installations, is very pleasing in appearance but is typically more expensive and requires a higher degree of installation experience and expertise. Stone is also an excellent option but choosing the right stone is important. While many stone types will not experience significant moisture or thermal expansion, some can be affected by pool chemicals and improper mineral balance in the pool water (see Section 11.3 for more information).

The installation of mosaic tiles in swimming pools and fountains has history going back thousands of years. In fact, the first tiled pools and baths incorporated small tesserae to create a variety of designs and mosaic murals. These tiles were installed individually, by hand, could take long periods of time and required installers with artistic ability to create. Fortunately, modern technology incorporates methods and materials to create beautiful installations quickly and easily. Stone, porcelain and glass mosaics are now pre-mounted, using several different methods onto sheets. These mosaics can even be customized to create a likeness of any picture or photograph using specialized computer software or exceptional artistic ability.

Figure 5.3 – Mosaic pool floor found in ruins of Pompeii, Italy.

In recent years the tile industry has seen some issues arise with the mounting of mosaic tile when used in submerged installations. To better understand this point, let’s look at the different ways in which tile and stone are mounted onto sheets;

Paper-face Mounted – paper face mounted tile, as the name suggests, are mosaic tiles that have a sheet of paper adhered to the face of the sheet of tile. This paper keeps the tiles properly separated and allows for the installation of the entire sheet at one time. Once the tile has been installed and has had sufficient time to cure (i.e. when the mortar holds the tile in place but allows for slight adjustments to be made in the tile) the paper is dampened and the paper is peeled off to reveal the tile finish.

Figure 5.4 – Two examples of paper-face mounted glass mosaic tile.

Plastic-face mounted – similar to paper face mounting except a clear plastic film is used in place of the paper. A great benefit of using the clear plastic film is that the tile or stone is visible through the plastic, and, if necessary, the plastic could be cut and adjustments made to the tile or stone prior to removing the film. In most cases, the plastic film cannot be removed until the setting mortar has fully cured.

Figure 5.5 – An example of plastic sheet mounted glass mosaic pebbles.

Rear Dot Mounted – some tile manufacturers use the method of mounting the tiles in sheets using polyvinyl chloride (PVC) dots. While this method eliminates the need to remove the paper face mounting, it carries its own types of concerns. Note the amount of space that the PVC dots cover on the back of each tile in Figure 5.6.

Figure 5.6 – An example of PVC dot mounted tile.

Rear Mesh Mounted – this method incorporates a fiberglass mesh which is bonded to the back of mosaic sheets to create the sheets. This method also eliminates the need to remove the paper face mounting but, it too, carries its own set of potential problems depending on the type of and the amount of mesh adhesive that is used.

Figure 5.7 – An example of rear mesh mounted glass mosaic tile.

Rear Paper Mesh Mounted – this method utilizes a paper mounting which is cut into a mesh configuration. While this method does eliminate the need to remove the paper from the front, it is not recommended, for obvious reasons, for use in swimming pools, fountains, spas, water features, or any wet area.

Figure 5.8 – An example of rear paper mesh mounted porcelain mosaic tile.

Installation of tile in swimming pools requires the tile to be fully and solidly bonded to the substrate. Simply put, this means that the tile should have 95 – 100% adhesive coverage not only to the back of the tile but also to the substrate. In submerged installations 95 – 100% coverage is essential to the long term performance of tile or stone. As stated in ANSI A108.5 2.4 Setting ceramic mosaic tile; “Thoroughly beat all tile or tile assemblies into place with a beating block to obtain maximum contact of bonding mortar on the back of each tile … where contact area shall be 95% when no less than 3 tiles or tile assemblies are removed for inspection”.4

Since maximum coverage is essential, the preferred tile mounting type for submerged installations would be the paper-face or plastic-face mounted mosaic sheets. Due to the fact that there are no obstacles to full adhesion (e.g. mesh and/or adhesive), 100% coverage can be achieved. PVC dot mounted mosaic sheets present 2 challenges for proper adhesion to the substrate; the PVC dots take up space on the back of each tile and PVC can be difficult for the tile adhesive to bond to. Keep in mind that the thin-set or epoxy used to bond the tile to the substrate must have 95 – 100% coverage to the tile and the substrate; not the tile, PVC dots, glue and/or mesh, and the substrate. If PVC dot mounted sheets are to be used then choose a type that has an average of less than 5% coverage of the PVC on the back of each sheet.

Another potential problem with PVC dot-mounted mosaic tile is how high the PVC dots are between each tile. If the dots are too high then grout does not have enough surface area to properly bond to the tile, or, there is simply not enough space for the grout to be properly installed. The PVC dots can also inhibit the bond of grout to the PVC.

In an effort to reduce costs, some mosaic tile manufacturers haphazardly use inappropriate glues, such as dilute polyvinyl acetate, to mount tile on backing mesh. As stated earlier these glues interfere with contact and bonding between mosaic tiles and the tile adhesive. When immersed in water these glues can soften and then swell as they absorb water, leading to loss of adhesion. This may occur within several weeks to several years but the result is almost always the same.5 Simply put, the use of back-mounted or dot-mounted sheet mosaic tiles may be precluded from use in submerged or exterior conditions if the sheet backing and/or adhesive adversely affects the development of adequate and permanent adhesion between the mosaic tile body and the bedding mortar.

Tile manufacturers must specify, in writing, whether their assemblies are suitable for installation in swimming pools, fountains, water features, exterior, and other wet areas. Paper back-mounted mosaics are not recommended in submerged or wet areas.6

There are 3 categories of glue to avoid;

Glues that soften without noticeable swelling as they absorb water. These appear to be clear when dry and white when immersed (similar to PVA wood glues).

Glues that soften and swell to a gel that eventually forces tile apart and away from the substrate and may fall apart in small pieces rather than stay attached to the mesh.

Glues that do not change in appearance or feel but gradually lose adhesion to the tile after prolonged immersion in water. Moisture evidently breaks down the adhesion without penetrating far into the film of glue.7

Figure 5.9 – A classic example of an improper adhesive used to mount the mesh for submerged installation. The adhesive has changed color from clear to white and has swelled significantly, forcing delamination.

For mesh backed mosaic tile the fabric mesh and the adhesive used to mount the fabric mesh must be water-resistant and chemical-resistant, should not weaken when exposed to moisture, should be resistant to varying pH levels, resistant to high alkalinity, and should be compatible with the mortar or adhesive used to bond the mosaics. It is the responsibility of the ceramic tile manufacturer to mount the tiles so that the bond requirements of ANSI A137.1, according to ASTM C482 “Standard Test Method for Bond Strength of Ceramic Tile to Portland Cement Paste” are met or exceeded.8 Beyond that, the architect/designer, tile installer and owner should also make sure that the products being used on the job are acceptable and adequate for the designed purpose. The installation of tile, which is meant for the purpose, using the appropriate setting materials will save time, labor and money and keep the swimming pool or fountain in continual operation for a very, very long time.

5.4 Non-Tiled Pool Finish Types

While tile and stone are beautiful and functional design elements for swimming pools and fountains, there are other finish options.

Plaster – pool plaster is an age old process for finishing swimming pools, fountains and water features. Plastering provides a more watertight seal than the gunite, shot-crete or poured concrete on which the plaster is installed. Pool plasters are often comprised of white portland cement and fine marble dust, known as Marcite or Marbleite, but there are now quartz based plasters that incorporate a fine, pigmented quartz aggregate and provide many color options. Plaster is pumped through a high pressure hose to the pool and is then troweled on by trained technicians. While plaster is a very popular finish for swimming pools, often used in conjunction with tile or stone at the water line, plaster must be replaced every so often. See Section 11.3 for more information on the causes of plaster problems.

Figure 5.10 – Typical Marcite plaster installation (notice the spiked shoes).

Pebble Tec – pebble tec pool finishes are similar to plaster or Marcite, except small river pebbles are mixed with the fine aggregate, white portland cement and pigments. This mix is pumped to the jobsite in a high pressure hose, troweled on by trained personnel and allowed to dry. The pool finish is then acid washed to remove the thin plaster coating which exposes the pebble aggregate and finished surface.

Paint – one of the most common, and least expensive, pool finish materials is paint. Pool paint is available in a wide variety of colors and can be used to create intricate designs. There are three types of paint which are suitable for use in swimming pools, fountains and water features;

Epoxy paint – epoxy paint is often used in new pool construction or in pools previously painted with epoxy, and is long lasting and durable. Epoxy coatings are effective against pool chemical attack, UV rays and automatic pool cleaners, and, a good epoxy paint will last approximately 7 – 10 years.

Chlorinated rubber base paint – rubber base paint is not as durable or expensive as epoxy paint, but is a dependable and easy-to-use coating material. Chlorinated rubber base paint is available in many colors and will last approximately 3 – 5 years.

Water-based acrylic paint – water-based acrylic paint is inexpensive, applies to almost any surface and cleans with water while still fresh. Available in a wide range of colors acrylic paints will last approximately 2 – 3 years before repainting is necessary.

Vinyl Liner – vinyl liners are custom made sheets of vinyl which are installed between the water and the pool structure. These liners lock into a track located on the bottom of the pool coping immediately under the deck. Vinyl liners provide good resistance to pool chemical maintained at proper levels but may fade or become brittle when harsh chemicals or high concentrations of chemicals are used.9

While all of the above mentioned finishes are effective and reliable, none of them have the durability and lasting beauty of tile and stone. Installed properly in a well cared for swimming pool or fountain, tile and stone can (and has) lasted for several millennia!

1 The Tile Doctor, How To Shop for Ceramic Tile. Retrieved 9/2/2008 from http://www.thetiledoctor.com/sh_ceramictile.cfm.

2 Pool Janitor FAQ, Retrieved on 9/17/2008 from www.poolcenter.com.

3 Endorsement of Portable Test Methods and Slip Prevention Standards for Existing Flooring, Ceramic Tile Institute of America, Culver City, CA, Retrieved September 15, 2008 from www.ctioa.org.

4 American National Standard Specifications for the Installation of Ceramic Tile Material and Installation Standards, ANSI A108 and ANSI A118 Series, American National Standards Institute, NY, 2008, pg 44.

5 Hartog, Peter, Tiling At The Deep End…Revisited. Retrieved 9/11/08 from www.tiletoday.com.au.

6 TCA Handbook for Ceramic Tile Installation 45th Edition. Tile Council of North America, Inc. Anderson, SC, 2007, page 12.

7 Hartog, Peter, Tiling At The Deep End…Revisited. Retrieved 9/11/08 from www.tiletoday.com.au.

8 Bulletin 3: Back-Mounted Ceramic Tile. Materials and Methods Standards Association, Houston, TX, 2005.

9 Vinyl Liners, Retrieved on 9/17/2008 from www.poolcenter.com.