By Gregory Mowat, Forensic Tile Consultants
Selecting the correct size of trowel for mortar application is a key requirement for any properly installed tile or stone project. Using the appropriate trowel increases efficiency and the quality of the finished product. Always check the trowel for excessive wear before using. Regular cleaning and proper storage will prolong the life of the tool.
Trowels are offered for a range of applications:
- Pointing trowels are ideal for tight corners and intricate detailing.
- Notching trowels are designed for applying thin-set mortars, ensuring even distribution of the mortar and excellent adhesion to tiles and stones. Square notched trowels are commonly used for larger tiles, while rectangular notched trowels are commonly used for smaller tiles.
- Flat trowels are suitable for spreading mortar and smoothing surfaces.
When working with thick, heavy-duty mortars use a sturdier trowel. Larger trowels are more efficient for covering large areas quickly, minimizing time and effort. Experienced tilers often use multiple trowel sizes for a single project. Switch between the trowels as needed to maintain precision and speed. A trowel that feels comfortable and balanced in the hand will lead to a more efficient work process.
Larger and heavier tiles will require more mortar to ensure adequate support and adhesion. Matching the trowel size to the scale and detail of the project is very important. The best way to determine the ideal size for a specific application may involve trial and error. When in doubt, call the mortar manufacturer, read the instructions on the bag of mortar to be used, or ask the tile manufacturer and/or distributor.
Neither flat-back nor notched-back troweling should be construed as acceptable methods for spot bonding tiles. When mortar is notched to the tile back, the ridges must be collapsed when placed to create adequate coverage. When mixing, proper mortar consistency is achieved when ridges formed with the recommended notched trowel do not slump. Follow the mortar manufacturerโs direction and apply ridges perpendicular toward the short side of the tile.
Also, be aware of a known issue with the ยฝโ by ยฝโ notched trowel. According to the National Tile Contractors Association (NTCA), โan issue with the trowel, which was introduced to the tile industry with the intention of providing additional mortar to facilitate the installation of larger tile, is the distance between the notches. The wide space between them makes it difficult, if not impossible, to fully collapse the mortar ridges into valleys. A specified grout joint width of 1/16โ to 1/8โ limits the ability to move the tile back and forth.โ
ANSI A108.5 lists the following guidelines for setting ceramic tiles with dry-set cement mortar, modified dry-set cement mortar, EGP (exterior glue plywood) modified dry-set cement mortar or improved modified dry-set cement mortar:
- Use the flat side of the trowel to key mortar or adhesive into the substrate to achieve the best possible mechanical bond.
- Comb in one direction with the notched side of the trowel, holding the trowel at a 45ยฐ Installation specifications require no less than 3/32โ adhesive between the tile and substrate after proper bedding.
- It may be necessary to flat-back trowel individual tiles or tile assemblies with bond coat to achieve the proper coverage.
- Set tile with a sliding motion perpendicular to the mortar ridges.
- The 95% coverage in exterior and wet areas, or 80% interior, shall be sufficiently distributed to give full support to the tile with particular attention to the support under all corners and edges of the tile.
- Installer must periodically remove sheets or individual tiles to assure proper bond coverage consistent with industry specifications. Lack of adequate coverage may be due to improper bedding of the tile, inconsistent angle of the trowel during application or use of a wrong trowel.
- Button-back, lugged or key-back tiles require special attention.
These guidelines cannot address every installation circumstance. The substrate, type and size of tile, intended service level of the installation, climate conditions, interior or exterior use and individual manufacturerโs recommendations are all factors the installer should consider in selecting the proper trowel.
Always work toward successful tile and stone installations.
