by Ofentse Sefolo

Large-format tiles are in high demand for a variety of reasons. Designers like the aesthetically pleasing, open look they lend to residential and commercial applications. Consumers like the natural beauty of a large expanse and appreciate the easier maintenance resulting from fewer grouted joints. However, large-format tile also has its installation challenges.

Advanced installation materials and techniques have improved the overall quality of large-format tile installations while helping to improve the installer’s efficiency. Keeping up with the latest in products and techniques will help installers produce aesthetically pleasing – and profitably installed – tile on floors and walls.

• Type of application. Is it an interior or exterior application? Is it expected to be wet (e.g. a shower or steam room) or relatively dry (e.g. a conference room)? Is it a commercial building or a residence?
• Potential use. Will the installation be subject to heavy commercial traffic? Will the floor be subject to extreme temperature?
• Substrate. Can the intended substrate support the weight of the tile with an acceptable amount of deflection? Is the substrate flat?
• Type of tile. Is the specified tile highly porous, such as limestone, or less water absorptive? Highly porous tiles, especially, will require a sealer to protect the beauty of the installation.
• Installation materials. Will the selected materials meet or exceed the requirements of the installation method and not negatively affect productivity?

Large-format tile presents several challenges when used in floor installations. Some of the common concerns are:

1. Tile weight.
Heavy stone floor tile that settles into the adhesive 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 the worst case, it can be a tripping hazard.

A substrate that is not perfectly flat to begin with will exacerbate an uneven floor problem as the tile is installed.

2. Secure bonding.
It is crucial to achieve secure bonding between the substrate and the large-format 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 adhesive in that area of the tile.

3. 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.

4. Ensuring a flat substrate.
Many tile installation problems happen because the substrate or subflooring is not ready or lacks the proper preparation. If you have no other option but to install tile over other types of material, make sure you verify the following:
• Check the existing tile to make sure there are no loose or chipped tiles that can prevent proper adhesion.
• It is extremely important to level the surfaces. If not level, you can use a grinder, sander or a tile level system.
• Create a rough surface to improve bonding. The existing surface needs to show some sort of roughness that will facilitate bonding between the new adhesive and the old surface.
• Use a vacuum to remove all dust, clean with water and remove all debris from the surface.
• Use an epoxy or other adhesive material recommended for this type of installation and surface. These can help you avoid common tile installation problems later.
• Always prepare the subfloor!

The use of a self-levelling substrate 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.

5. Toward better bonding.
To achieve an adequate bond for large-format floor tile, the bonding material must evenly and thoroughly cover the area beneath the tile. Using a large trowel will help to ensure that the adhesive 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 adhesive.

Although back-buttering is still widely accepted, the formulation of the new performance adhesives makes it possible to achieve excellent coverage without applying additional material.

Some of these new adhesives are formulated with exceptionally fine particles – or nanostructures – that line up like interlocking puzzle pieces in the wet cement in the adhesive to achieve high cohesive strength. Additionally, the ceramic microspheres interact with the cement resulting in stronger bonds.

When working with large-format tile, combing the bonding adhesive with parallel ridges and then pressing the tile perpendicular to the comb marks yields the best result.

6. Preventing cracks.
Use of a crack-isolation system will prevent shrinkage cracks from migrating from the substrate into the installed tile. Shrinkage cracks are of 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 adhesives. Crack-isolation membranes are installed directly to the substrate. After allowing appropriate drying time, the tile is set with a supportive adhesive such as a medium-bed or a performance adhesive. The installation process requires two or three steps with sheet membranes and two steps with roller-applied liquid or trowel-applied membranes.

Final word
Technology is constantly evolving and so too are the tools and gadgets that can simplify your next large-format tile installation. Laser measurement tools, tile layout software and other new technology will help you to understand how the shape of the room affects the installation process.
However, many tile installation problems come precisely from inaccurate floor layout. Knowing your tile and room dimensions is the first step to completing a flawless project.

For more information visit www.mapei.co.za.

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