What the Trowel Does
Tile is not simply stuck to a surface. It sits in a bed of adhesive, usually a cement-based mortar often called thinset, or a premixed organic adhesive for some wall tile. The adhesive needs to be spread in an even, consistent layer with full contact under the tile. A notched trowel does this by leaving parallel ridges of controlled height. When the tile is pressed down, the ridges flatten and collapse together to form a continuous bed.
This is why the trowel is one of the most important tools in tile work. It controls how much adhesive goes down and how well it supports the tile. This article covers trowel shapes and sizes in general terms. Adhesive and tile manufacturers publish their own recommendations, which take priority.
Parts of a Notched Trowel
A notched trowel is a flat steel blade with teeth along one or more edges and a handle. The flat side moves the adhesive, and the notched edge combs it. Some trowels have different notch sizes on each end, which can be handy, and a good handle is worth having since you may spend hours gripping it.
Notch Shapes
Square-notch. Teeth have square gaps and flat tops. They leave tall, straight ridges and are common for floor tile and larger formats because they hold a generous amount of adhesive.
U-notch. Rounded notches that leave rounded ridges. They are often used with thin or flexible products, and sometimes with certain adhesives that call for them.
V-notch. Triangular notches that leave small, pointed ridges and a thin bed. They are often used for small wall tile and mosaics where less adhesive is needed.
Which shape is recommended depends on the adhesive and the tile, so look at the packaging. As a rough rule, larger and heavier tile generally needs deeper notches, and small tile needs shallower ones.
Notch Size
Notch size is listed as the width and depth of the teeth, usually in fractions of an inch or in millimeters. A larger notch leaves more adhesive. The goal is enough material that the tile has full contact after being pressed in, without so much that adhesive squeezes up through the grout joints.
Large and uneven tile often needs a bigger notch because the back is not perfectly flat. Some jobs also call for back-buttering, which means spreading a thin coat of adhesive on the back of the tile with the flat side of the trowel before setting it. Many installers do this for large-format tile or when the product instructions require it. In wet areas and on exterior work, getting coverage right matters because voids can trap water, and the tile and adhesive makers typically publish coverage guidance.
Preparing the Surface
Before any adhesive goes down, the surface should be clean, flat and solid. A straightedge held across the floor reveals high and low spots, and lippage, the unevenness between neighboring tiles, tends to follow from an uneven base. Cracked or loose substrate, dust and old sealers can all prevent a good bond. The right substrate, such as cement board, a membrane or a prepared concrete slab, depends on the room and the tile, and manufacturers have specific instructions, so check them before starting. Set your layout lines first, using chalk lines and a dry run of tiles, so you know where to begin.
Spreading and Combing
- Mix the adhesive to the consistency the label describes, usually something like peanut butter. Let powder mixes rest (slake) if the instructions say so.
- Spread a small area. Use the flat edge to press adhesive firmly into the surface, keeping it to an area you can tile before the adhesive starts to skin over. The open time on the label tells you how long you have.
- Comb with the notched edge. Hold the trowel at a consistent angle, commonly around 45 degrees, and pull it in straight lines in one direction. Keeping the ridges parallel allows air to escape when the tile is set.
- Set the tile. Place it into the ridges and press with a slight sliding motion perpendicular to the lines, so the ridges collapse.
- Check coverage. Lift a tile occasionally and look at the back. The adhesive should cover most of it with no large empty areas. If it does not, adjust the notch size, the angle or the technique.
- Use spacers and a level or straightedge to keep joints consistent and surfaces flat.
If the adhesive has formed a skin, scrape it up and spread fresh material rather than setting tile on it. Clean adhesive off the face of the tile and out of the joints while it is still soft.
Other Setting Tools
- A margin trowel for small spaces and mixing.
- A rubber mallet or beating block to seat the tile evenly without cracking it.
- Tile spacers for uniform joints.
- A rubber grout float and sponge for the grouting step that follows once the adhesive has cured.
- A bucket and mixing paddle with a low-speed drill, used carefully to keep the mix consistent.
- A cutter for fitting edge pieces, which is covered separately with scorers and saws.
Clean your tools soon after use because hardened mortar is hard to remove. Wash them in a bucket, not a household drain, and dispose of waste according to local rules.
Safety
Cement-based adhesives are alkaline and can irritate skin and eyes, so wear gloves and safety glasses. Mixing powder releases fine dust, so a dust mask or respirator helps, and ventilation does too. Knees take a beating on floors, and kneepads reduce strain. Allow the adhesive to cure for the time listed before walking on the floor or grouting. Results depend on the product, the room’s conditions and the preparation, so follow the manufacturer’s instructions throughout.