Do You Need Underlayment for Tile Installation?

Installing ceramic or porcelain tiles? Learn why you need an underlayment for your tile installation project - what it does, what types are available & more!

Do You Need Underlayment for Tile Installation?

Installing a tile floor can be a tricky process, and one of the most important steps is to make sure that the tile is properly supported. A base membrane, also known as an underlayment, is a layer of material that is placed between the subfloor and the tile to help prevent cracks in the tile from transferring to the newly installed tile. This is the industry standard preferred by construction professionals when installing ceramic or porcelain tiles. The base membrane comes in four foot by eight foot and three foot by five foot rigid panels that contain a combination of cement, fiberglass and sometimes crushed glass particles.

Professionals install the support plate on a thin layer (an adhesive), a process called bedding. Then, the support plate is secured with screws to the lower subfloor. An additional thin-layer layer is applied to the surface of the support plate and used to fix the tiles. This is a very effective way to install tiles and the best way to ensure that it doesn't crack.

Thinset mortar, also known as fine mortar, should not be confused with regular mortar. Thinset is made of cement and contains polymers and adhesive agents that adhere firmly to the tiles. It comes in powder form and must be mixed with water. It is applied with a notched trowel to the surface of the support plate or to a concrete slab.

As long as the concrete slab is very flat and does not contain cracks, the tiles can be installed directly on top, using a thin layer as an adhesive, which allows the support layer to be omitted. If the tile is uneven or cracked, it must first be patched and leveled before the tile can be installed. Flexible polyethylene coating membranes come in rolls and are designed to offer some protection against water and cracking (depending on the specific product). They are used instead of the support plate, but are installed in a similar way.

Decoupling membranes, such as DITRA (available on Amazon), also manufactured by Shulter Systems, replace traditional support plates in wooden subfloors and concrete slabs. They are designed to absorb imperceptible amounts of movement of the substrate and prevent tiles from cracking. Like support plates, decoupling membranes are embedded in a layer of thin material and then another layer of thin material is applied on top to fix the tiles. These products should help prevent any cracks in the tile from damaging the newly installed tile.

The membrane not only protects against cracking, but also serves as a vapor management system and protects the substrate from moisture penetration. Exterior plywood is an acceptable base for tiles and is preferred to interior quality plywood because the bonding adhesives used are waterproof. They are typically used as a base in tile showers to prevent water from seeping through cracks in the concrete shower base. Cement-based backboard is largely regarded as the best subfloor for ceramic tiles in any application: floors, walls and countertops.

Sheets are a new and innovative product on the market that consists mainly of cement-based materials that act as a subfloor. Vinyl floors that are too bright or padded don't work very well as a subfloor for ceramic tiles. If there are cracks or uneven areas in the concrete below, it is essential to seal them with an undercoat before installation. There are several types of tile subfloor available that can be poured and can be used with a pallet, each with its own purpose and best use.

Plywood sheets are placed on top of an OSB (or plywood subfloor) to obtain a two-layer base. Before installation, read the installation instructions carefully to determine if the joists and subfloor are suitable for this type of tile subfloor. It is important that seams do not overlap between layers and it is recommended that screws that hold upper subfloor do not reach joists on floor, since it is necessary to allow certain degree of lateral movement.

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