Large Format Tile - Installation Advice
Large format tile has become very popular. Designers like the aesthetically pleasing, open look it gives floors and walls. Consumers like the natural beauty of a large stone expanse and appreciate the easier maintenance resulting from fewer grouted joints. But large-format tile also has its installation challenges. Most importantly working with large-format stone requires tighter tolerances in the substrate. In addition, its weight makes it harder to handle in both floor and wall applications.
When they were first introduced to the industry, “large-format” encompassed any tiles that measured larger than Now, after roughly a decade of development, “large-format” generally viewed as any tiles larger than the fairly standard 60 x 60cm (24 x 24") and includes very large tiles up to and even larger than 1 x 3m (40 x 120").
When these types of tiles first began picking up momentum in the industry, the term “thin porcelain tile” was coined because they were mostly used for walls, but this term is no longer in use as large tiles are available in all kinds of thicknesses and are suitable for floors too.
Large Format Installation
Large-format tile presents several challenges when used in floor installations. Some of the common concerns are:
Tile weight is the primary challenge. Heavy stone floor tile that settles into the mortar bed can cause 'lippage' - a condition where one edge of a tile is higher than adjacent edges. The result is a finished surface that has an uneven appearance. In a worst case, it is an uneven floor that causes a tripping hazard.
In addition, it is crucial to achieve secure bonding of the substrate and the natural stone tile flooring. Applying an insufficient amount of material may result in hollow sounding spots. The hollow spot is susceptible to damage from concentrated weight because of a lack of support from the mortar in that area of the tile.
Cracking is a possibility if the tile is bonded directly to concrete. This is because cracks naturally occur as water in the concrete substrate evaporates. These shrinkage cracks can transfer from the substrate and into the bonded tile. Cracking can also occur from improperly installed wood subfloors.
Medium-bed mortars are a common solution to support large-format tile and prevent lippage. These mortars are formulated to keep the tile from slumping into the mortar bed and to not shrink as the mortar cures. Often used in installations up to 10cm thick, medium-bed mortars may require a polymer additive to bond with some substrates. Because medium-bed mortars can be difficult to trowel, installers often add more water, which can adversely affect the mortar's non-slump performance and its bonding ability.
New types of performance mortars prevent large-format tile from slumping and are easier to use than traditional medium-bed mortars. Some of these mortars are formulated with hollow, ceramic microspheres that are not only lighter in weight but produce a ball-bearing effect - resulting in minimal trowel resistance and better labor productivity. The microspheres also provide buoyancy, which helps contribute to the non-slump properties.
Ensuring a flat substrate
Use of a self-leveling underlayment is the most efficient way to attain a uniformly flat substrate, particularly over a large area such as an entire room. These products are cement-based and may be poured or pumped onto the affected area. Smaller substrate corrections may be made with latex-modified floor patch products. To ensure compatibility, the industry recommends that substrate preparation products come from the same manufacturer as the rest of the installation system.
A 3m level or straight edge will help measure possible variation in the substrate, and these tools are also useful in making sure that installed tile is flat.
To achieve an adequate bond for large-format floor tile, the bonding material must evenly and thoroughly cover the area beneath the tile. Use of a large notched trowel will help ensure that the mortar adequately covers the substrate.
A long-standing installation practice is to back-butter each piece of tile. While effective at attaining 100% coverage, it is time consuming and requires extra mortar.
Although back-buttering is still widely accepted, the formulation of the new performance mortars makes it possible to achieve excellent coverage without applying additional material. Some of these new mortars are formulated with very fine particles - or nanostructures - that line up like interlocking puzzle pieces in the wet cement in the mortar to achieve high cohesive strength. Additionally, the ceramic microspheres interact with the cement, resulting in stronger bonds.
Use of a crack-isolation system will prevent shrinkage cracks from migrating from the substrate into the installed tile. Shrinkage cracks are a particular concern in relatively new concrete, as an estimated 80% of shrinkage cracks occur within the first year after the substrate is poured.
Crack-isolation systems are available as membranes (sheet, roller-applied liquid or trowel-applied) and as one-step mortars. Crack-isolation membranes are installed directly to the substrate. After allowing appropriate drying time, the tile is set with a supportive mortar such as a medium-bed or a performance mortar. The installation process requires two or three steps with sheet membranes and two steps with roller-applied liquid or trowel-applied membranes.
One-step mortars, which are formulated to isolate cracks and set tile in a single step, may also be used to install large-format tile. These products require less labor and materials than crack-isolation membranes. Some one-step mortars will isolate cracks up to 3mm wide.
Wall installation challenges
Installers also face a variety of challenges with large-format wall tile. Here are some common areas of concern:
Gravity is the primary challenge. The weight of a large-format stone tile can cause it to sag or slip during installation on the wall.
Having a flat (or plumb) substrate is also critical. Again, the maximum tolerance is 3mm in 3m. If this tolerance isn't met, lippage can occur. Wall installation lippage can be both a structural and an aesthetic concern.
As with floors, secure bonding is key to the success of a large-format tile wall installation. The failure of a heavy tile to adhere to a wall can be a potentially dangerous issue.
Moisture between the stone tile and the substrate can also be an issue, particularly if the installation is in a wet area, such as a shower or steam room.