Ceramic Tile Flooring in Basements

A basement with ceramic tile floors

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Ceramic is a water-resistant, resilient, easy-to-maintain flooring option that is appropriate for many below-grade basement installations. However, there are some precautions that need to be taken during and after installation to ensure the integrity of the floor. There are also certain risks associated with using almost any material in a below-grade environment, and ceramic tile is no exception. As with most flooring, water is a principle enemy in a basement.

Preparation

Most other flooring materials—including hardwood, laminate, or carpet—will perform best in a basement environment if they are installed over a subfloor of DRIcore, or plywood or OSB elevated slightly on sleeper boards. But for ceramic tile, the best subfloor is the cement slab itself—provided the slab is stable and in good condition. A cement slab serves as a sturdy mortar bed, and ceramic tile will adhere to it quite well with thin-set adhesive. Expansion joints in the concrete pose a problem, however, since if ceramic tile is laid over the expansion joints, movement in the slab can cause the tile installation to crack. To prevent this, an uncoupling membrane can be used, which is laid over the concrete slab before the tile is installed.

Before actual installation beings, the cement subfloor needs to be carefully prepared, since the integrity of the subfloor will affect the entire life of the ceramic floor above. The subfloor should be smoothed out, sanded, and made completely flat and even. If there are dips or cracks, self-leveling underlayment (SLU) compound—a cementitious dry powder that is mixed with water—should be used to repair and fill them. If there are gaps or rises in the subfloor, these can become weak points lurking beneath the tiles. When an uncoupling membrane is also being used, the floor should be leveled and repaired before the membrane is laid down.

In basement environments, installing a plywood subfloor is not a good choice for tile—even as a base for cement board—since moisture or water vapor bleeding up through the slab can warp and rot the wood.

In most cases, the smooth surface of the concrete will then have to be scarified slightly in order to give it texture ("tooth") that the thin-set tile adhesive can bond to. This can be done with a power sander and coarse sandpaper. Any resultant dust or debris then needs to be removed with a vacuum before laying the tile.

Installation Overview

In basement locations, ceramic tile is generally glued down to the cement subfloor using the same thin-set adhesives used to apply tile to the cement-board underlayment used over plywood or OSB subfloors. Installation procedures involve simply following the tile and adhesive manufacturer's directions.

Thin-set adhesives make DIY installation perfectly possible, though professional installation is always an option. This is purely a personal choice, and in a basement environment, you may well want to consider having a professional do the work. Ceramic tiles are heavy, and you will have to carry them down the stairs yourself and then painstakingly lay each piece, one by one. There will be tile cutting required, which is best done with a power wet saw—a tool that pros routinely use. The entire installation process can take several days and needs to be done right to ensure the strength of the floor after it is complete.

Bottom line: Do this work yourself only if you are confident in your endurance and your tiling skills.

Ceramic Tile: A Cold Material

Although there are many advantages of ceramic tile in a basement, there is one notable problem: Ceramic tile is a cold material underfoot, and this characteristic is exaggerated by the fact that below-grade basements are already chilly. Ceramic tile installed over a concrete slab readily transmits heat from the living space into the earth, which can make it difficult to keep the space comfortable.

The very best solution, although a somewhat expensive one, is to install a radiant floor heating system over the concrete slab before installing the tile. There are two types of systems available:

  • Hydronic systems: Warm water circulates through plastic tubing beneath the surface flooring. Hydronic systems are more expensive and are typically most practical where there is a boiler system already in place that can be extended to circulate hot water beneath the floor.
  • Electric mat systems: Radiant coils beneath the flooring are heated by electrical current. The plastic tubing or electric coils are typically embedded in mortar before the tile is installed. Electric systems are less expensive to install, but they are more expensive to operate over the long run.

Both forms of radiant heating systems are remarkably effective, turning normally cold ceramic tiles into a surface that provides delicious warmth to the room.

Where radiant flooring systems are not practical, most people simply rely on covering the ceramic tile floors with plush area rugs to create both warmth and softness. Well-chosen rugs can also serve as a design element in a basement living space.

Ceramic Tile and Water

Basements are by nature subject to moisture, both because of humidity from condensation and migration of water vapor through the foundation walls and slabs, and because these below-ground locations are subject to flooding. Most ceramic tiles are themselves virtually immune to water damage, since the glazed surface is impervious to moisture. Even in total and prolonged immersion in water, glazed tiles remain immune to damage, which is one reason why ceramic tile basement floors are a very good choice where flooding is an ongoing threat.

But if moisture seeps through the grout in the joints between tiles, it can degrade the thin-set adhesive used to secure the tile and cause the floor to fail. The grout used to fill the joints between tiles is not naturally waterproof, so it needs to be sealed to prevent moisture infiltration. Finally, moisture can also cause the growth of mold and mildew in the grout lines, unless they are sealed.

Therefore, basement ceramic tile installations need to be treated with a quality water-barrier sealer to create an impervious, invisible layer across the tile and grout. This will stop any liquids from penetrating through the grout lines or any cracks in the tile. This sealer level is even more important with terra cotta tile and other types of unglazed ceramic or stone. This sealer coat needs to be reapplied periodically—every six to 12 months. If this sealer layer is intact, it will protect the floor and prevent damage, even if the floor is fully flooded. There are many cases where a ceramic tile basement floor is immersed in water for weeks and still emerges unscathed once floodwaters recede and the floor is cleaned.

In Case of Flood

If your ceramic tile does experience a flood, remove the standing water and dry things out as quickly and possible. Water left standing in a basement can lead to mold problems later on. The ceramic tile floor will be less problematic than the drywall, wood trim, and furnishings when it comes to mold and mildew. Open all windows and use fans to circulate humid air out of the space. A dehumidifier can also be used to remove lingering moisture in the air.

Next, determine the extent of damage, if any, to the ceramic tile and grout. If grout lines are compromised, they may start to dissolve and crumble away. Dissolving grout can be removed with a grout saw, then replaced with fresh grout once the entire area is fully dry again.

If the water penetration is very extensive, then the thin-set adhesive beneath the tile may start to loosen. This will require you to remove, clean, and replace the affected sections of flooring.