Working with Large-Format Tiles
These sizes are ideal for covering the conical slope of shower floors with little or no lippage and bare feet help spread out compressive loads. Even though these small porcelain tiles have exceptional compressive strength, outside the shower environment, 1”, 2”, or 3” tile installations have relatively low resistance to point loading, and therefore are not the best choice for general flooring applications.
One of the reasons that large-format tiles have been difficult to manufacture is that relatively wet tile bodies tend to shrink, warp and wedge while they are being fired in a kiln. To counter this, manufacturers now use the dust-press method. Dust-pressed tile bodies contain only enough moisture to remain cohesive during the entire manufacturing process, and some brands are amazingly flat and distortion-free. Porcelain tiles in 24” and 36” formats are available now, and as technologies improve, no doubt tile sizes will continue to grow.
Also available are thin porcelain panels designed to be installed over sound, existing tile installations. Although these panels – some of which measure an amazing 1 meter by 3 meters and approximately 3/16” thick – are not considered tiles in the classical sense, they nevertheless exhibit properties shared by porcelain tiles such as stain-resistance, durable surface and high compression strength. Very large-format porcelain panels require special installation equipment and methods that are not covered in this article
Installing Large-Format Tiles
Attention to details is essential for a successful installation, and I begin a large-format tile installation with a careful layout. Thin cuts are especially unattractive – even if they are larger than half size – so I prefer to use whole tiles only, or those with minimal cutting. I enjoy using 24” tiles, but I use 18”, 16”, or 14” tiles to minimize cutting.
A super-expensive bridge saw is not necessary when large-format tiles have to be cut. Porcelain tiles have an undeserved reputation for being difficult to trim on a snap cutter, but by painting the score path with kerosene or a low viscosity oil beforescoring, straight cuts are easy (Photo 1).Snap cutting can be done indoors without creating a mess, plus the tile back remains dry and can be installed immediately without having to deal with towels or sunlight to dry the back.
Diagonal cutting a 24” tile requires a very large wet saw, but I use a dry-cutting diamond blade in a small circular saw with a straightedge and a couple clamps when working with large-format tiles (Photo 2). To minimize chipped edges, I keep the sole plate of the saw in constant contact with the straightedge, and instead of cutting the tile with one pass, which can cause heat-stress breakage (and shorten the life of the blade), I set the blade depth to make several light passes. For circular cuts, I use a diamond blade mounted in an angle grinder, and make several light stock-removal passes to minimize chipping or cracking (Photo 3). When practical, I like to make as many cuts as possible before I start installing tiles (Photo 4).
When working with large-format tiles, I have found the installation goes a lot smoother if I spread only enough thinset mortar for one tile (Photo 5).As well, I back-butter each tile with a thin, hard-pressed film of thinset mortar to improve adhesion, and, depending on the flatness of the substrate, add additional mortar to the back of the tile with a notch trowel (Photos 6 and 7).
On either a wet-area wall or a wet or dry floor, 95% adhesive coverage is needed with total coverage at the corners. With large-format tiles, I check each one for proper coverage, and use a soft wood wedge (Photo 8) to pry the tile off the surface. Because of the mortar’s thicker cross-section, a medium-bed thinset mortar is recommended (organic adhesives should neverbe used to install large-format tiles!), and it is good practice to give the mortar extra time to setup and harden (Photo 9).
Installation of large-format tiles can cover a large area quickly, but the substrate (or setting bed) has to be smoother than if small tiles are being installed. Small size tiles – using 1” mosaic tiles as an extreme example – can easily follow the contours of a less-than-perfect surface with little or no lippage. Large-format tiles, however, can magnify surface irregularities and create a lippage nightmare.
With the industry flatness standard for regular size tiles at 1/4” in 10’, to ensure a smooth finish when installing large-format tiles the flatness standard has to be tightened incrementally as the tile size increases from 10” up to 24” and larger. When 16” to 24” tiles need to be installed, a quality self-leveling underlayment is highly recommended.
In my experience, most square large-format tiles are flat enough to be installed with a broken (or staggered) joint. With rectangular shapes, though, broken joint layouts with a 50% offset should be avoided because rectangular large-format tiles are often bowed. Thus a broken joint layout positions a tile’s high points (the corners) right next to the neighboring tile’s lowest point (the middle of the tile). Depending on the degree of bowing, the offset should be reduced to 40%, 30% or no offset at all.
Large-format porcelain tiles can be used on walls or floors (if made for floor use), but one of my favorite locations for this type of tile is on a countertop (Photo 10).The 24” tiles provide a smooth surface that is practical to work on, and with grout joints at 24” intervals, easy to keep clean, too. Large-format tile installed on a countertop are also an excellent alternative to stone slabs.
Wherever they are used, large-format porcelain tiles are extremely durable with a long life expectancy. With fewer grout joints, they are easy to maintain, and if installed carefully, they make a stylish addition to any home or commercial building.