Thinset is a type of adhesive compound that is commonly used to install various materials such as tiles and bricks onto substrates like walls and floors. Thinset is a blend of cement and sand, combined with certain additives and polymers that enhance the mixture's flexibility, workability, and adhesion.

How is thinset used?

Thinset mortar is a type of adhesive that is commonly used for installing tiles. It is specifically designed to bond these materials to a cementitious substrate. This product is effective on various surfaces including cement, concrete floors, walls covered in cement backer board, or a waterproof membrane placed over these materials.

To apply thinset to the floor or walls, you may use a notched trowel. In the case of larger tiles, it is recommended to apply thinset to both the surface and the back of the tile. The notched trowel is used by installers to create grooves or ridges in the thinset. This helps to release air as the tile is laid and pressed into place.

Advantages of thinset

  1. Easily accessible and reasonably priced
  2. Thinset materials, such as cement and sand, are readily available. Thinset is a cost-effective adhesive option compared to other types of adhesives, particularly synthetic materials or glues that utilize advanced polymers. The cost may not be a significant consideration in smaller areas such as backsplashes or inlays. Using thinset instead of pre-mixed synthetic adhesive can result in significant cost savings when covering a large floor area.

  3. Flattens the surface out
  4. Thinset is capable of easily filling minor imperfection in a subfloor due to its consistency. Thinset adhesive is preferred over glue-based adhesives because it smoothly glides off the blade of a trowel and fills in any low spots or dips, resulting in a more even surface.

  5. Takes a long time to set
  6. Thinset adhesive typically has a longer setting time compared to other types of tile adhesives. Although it may appear to be a disadvantage, it actually provides additional time to spread the mixture before it solidifies in the container. The extended set time allows the user to have ample time to lay and adjust tiles, resulting in a flawless installation.

  7. Water-resistant
  8. When it's fully cured, thinset outperforms mastic and other tile adhesives in its resistance to moisture. Thinset may be made chemically resistant with the addition of the correct chemicals, making it a viable option for use in commercial or industrial tile installations.

Disadvantages of thinset

  1. Inflexible
  2. Once thinset has dried, it cannot be easily reworked. Any bending of the subfloor or substrate can cause the thinset to separate from the tile if it isn't strong enough. In the same way, stepping on one end of a huge tile can cause the other end to pop loose if the thinset wasn't spread properly.

  3. Thinset isn’t visually appealing
  4. Most people won't want to use thinset, with its typical gray and drab appearance, behind glass tiles. Because it allows the tile's color to stand out without overpowering the glue, white mastic is often the ideal choice for these kinds of installations.

  5. Might be too runny
  6. While thinset is useful for walls, it may be too costly to utilize unaltered thinset for installing tiles vertically. To secure these tiles, an installer may need to use a "low slump" thinset or a stickier compound like mastic.

How much thinset do I need?

The entire area of your project and the tile size you plan to install will determine the amount of thinset you will require. Thicker thinset is required to support larger tiles, while thinner thinset can be used to attach smaller tiles. Using a notched trowel to spread thinset in even beads throughout the substrate allows for uniform thickness across the board.

The size of the beads produced by a trowel is determined by the size of its notch. During tile installation, the beads are flattened which reduces the likelihood of air getting trapped between the tiles and the substrate. The table below can serve as a guide for determining the appropriate trowel size and thinset thickness to use for different tile sizes:

Tile SizeNotch SizeThinset thickness (inches)Thinset thickness (m)
2 in x 2 in (5 x 5 cm) and smaller3/16 in x 5/32 in (5 x 5 mm) V-notch1/9 in0.002
4 in x 4 in (10 x 10 cm) and smaller1/4 in x 3/16 in (6 x 5 mm) V-notch1/9 in0.0024
8 in x 8 in (20 x 20 cm) and smaller1/4 in x 1/4 in (6 x 6 mm) square-notch1/8 in0.0035
8 in x 8 in (20 x 20 cm) and smaller1/4 in x 5/16 in (6 x 8 mm) U-notch1/7 in0.004
12 in x 12 in (30 x 30 cm) and smaller1/4 in x 3/8 in (6 x 9.5 mm) square-notch1/5 in0.005
12 in x 12 in (30 x 30 cm) and smaller1/4 in x 3/8 in (6 x 9.5 mm) U-notch1/5 in0.005
12 in x 12 in (30 x 30 cm) and larger1/2 in x 1/2 in (13 x 13 mm) square-notch1/4 in0.007
12 in x 12 in (30 x 30 cm) and larger1/4 in x 1/2 in (6 x 12 mm) U-notch1/4 in0.007
12 in x 12 in (30 x 30 cm) and larger3/4 in x 5/8 in (19 x 16 mm) U-notch1/3 in0.008

Although there are various notch shapes and sizes available in the market today, the ones mentioned above are the most commonly used. The table clearly indicates that smaller trowel sizes are suitable for smaller tiles as they provide thinner thinset thicknesses, whereas larger trowel sizes are appropriate for larger tiles as they offer thicker thinset.