Clearly Beautiful, Too

Last month, award-winning tile contractor Greg Andrews discussed the requirements for preparing a pool shell to receive glass tile. Once the pool is waterproofed, .oated, and the fittings are set, it's ready for tile installation. — Ed.

Glass mosaic refers to small-size glass tiles — generally speaking tile that's less than 2 inches. To make installation easier, the small tiles are assembled into foot-square sheets so that the entire sheet (which might contain 144 1-inch tiles) can be placed at one time rather than setting each tile individually.

Glass mosaics are generally mounted on sheets in one of three ways.

1. Paper-face mounted. The face of the tile is adhered with water-soluble glue to a sheet of paper, leaving the back of the tile completely exposed and available to contact the thinset. After the tiles are placed, the paper is moistened and removed before the adhesive sets, allowing the tiles to be adjusted if necessary.

2. Clear-film faced. These tiles are assembled with clear plastic adhesive on the face, which is removed after a final set is achieved. Adjustment is possible during installation by cutting through the plastic while the thinset is still fresh.

3. Back- and edge-mounted. These tiles may have perforated paper, fiber mesh, resin, polyurethane or other bonding material on the back or edges of each tile, which becomes part of the tile installation.

The Tile Council of North America's handbook for the installation of ceramic tile requires sufficient exposure of the tile body to allow for no less than 80 percent contact with the bond mortar in dry areas and no less than 95 percent contact with the bond mortar in wet areas. TCNA also requires that tile manufacturers must specify whether their assemblies are suitable for installation in swimming pools, on exteriors, and other wet areas.

After looking at back-mounted mosaic assemblies from literally dozens of manufacturers, I've concluded that at best 30 percent of the bonding surface is covered with glue and mesh, although the average seems to be about 50 percent.

With the requirement from the TCNA and all of the major thinset manufacturers at 95 percent coverage for submerged installations, I find that the only two options for backmounted assemblies are to not use them or to accept the responsibility for likely bind failure. At $50,000 to $150,000 per pool, the latter is not an option. Since glass is likely the most difficult material to bond, I personally refuse to use anything but facemounted assemblies in pools.

Artistically, I find that paper facemounted mosaics give me the freedom and ability to manipulate sheets, partial sheets, rows or individual pieces, which helps me conform to the ever-changing curvatures in pools.


The two most-common methods of adhering tile are the direct-bond method, which is just like you would set a porcelain tile in a kitchen or bathroom: The tiles are tapped into thinset adhesive, and once the bond is set, the spaces between tiles are filled with grout.

The other method, which I always use with paper-face mounted mosaics, is the alternate back-butter method. I apply the grout to the sheet of tile from the back side, forcing it into all the spaces between tiles, then apply the thinset to the wall, and then press the sheet in. Then at some point we wet the paper face and remove it, while the tile's still fresh.

I've found that using the alternate back-butter method of installing offers me the ability to move, shift, beat-in and manipulate sheets without the threat of having thinset come up through the joints and press up against the paper before it is removed — something that can add hours of scraping and cleaning to the installation, to say nothing about moving tiles out of place and losing bond.

This is not to say that the directbond thinset method isn't a great option. The challenge really comes down to the thickness of tile that's being used. There's a fine line between using the proper amount of setting material to achieve a 95 percent bond and having thinset protrude through the joints, and this threat obviously lessens as the tile thickness increases.

The 95 percent coverage is not only important for the bonding aspect of the installation, but also for the overall look of the tile in the long-run.

Since glass ranges from opaque to translucent to transparent, what we really have many times is a window or magnifying glass looking into the substrate, or setting material.

This can be devastating if voids or trowel marks start showing up in the weeks or months after an installation is complete due to the continued curing and shrinking that takes place in this time period.


After the pool is waterproofed, .oated and the fittings are set, it's ready for installation. The question is: Where do you start?

Basic layout concepts remain the same whether you're using glass, porcelain, stone or any other kind of mosaic. Unless you're dealing with a single-depth, vertical-wall pool, there will be radius corners, depth changes, and continuing dimension changes all the way down.

On most tile installations, I like to know where I'm going to end up before I start, but with pools, I've learned that things are a little different. I usually start at the waterline and work my way down toward the curvature that transitions into the .oor, and then I stop somewhere in that area. At that point, I turn my focus to the .oor and start working my way up toward the same area in the belly of the pool. Then I start making some decisions about where to start cutting in. I find this to be one of the "unknown" areas in which the pool actually tells me what to do. Many times, design features can help with those decisions; for instance, a design feature such as a medallion in the bottom of the pool is always a good starting point to work the .oor from. Other design features, such as an accent around the perimeter of the pool, can serve as a stopping point for both the walls and the floor, making the installation appear seamless.

When it comes to the actual installation of the tile, the method is going to be up to the installers and what they are comfortable with. As I've already mentioned, my preference is the alternate back-butter method, but since there's a learning curve to get through, I don't recommend it unless you've worked with someone who has experience with this system.

Since glass tile, along with its beauty, presents us with a new set of challenges, I offer the following installation reminders.

1. Always use thinset that meets or exceeds standard A-118.4.

2. Use proper troweling techniques including burning in the first coat of thinset with the .at side of the trowel, combing it out with the proper size notch for the tile to insure 100 percent coverage, then .attening out the notches just prior to installing the sheet.

3. Beat in each sheet, eliminating any voids in the setting material and creating a positive bond between the substrate and the tile.

4. Make any adjustments before the thinset has set, being careful not to break the bond.

5. Allow proper cure time before filling the pool with water. This is usually 14 to 21 days, depending on the manufacturer. This is a common mistake, as most owners are anxious to start swimming.

While most pool builders will subcontract tile installation that goes beyond a waterline trim, it's important to know enough about the process to choose a good subcontractor and then work effectively with him or her.

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