A variation of a square-notch trowel is the U-notch trowel. This delivers a bit less mortar than a square-notch and can be used wherever a square-notch makes sense. V-notch trowels have a continuous zig-zag or sawtooth pattern with points. They are typically used for small tiles, such as mosaics , or any tiles under 2 inches square. Because V-notch trowels dispense less mortar than square-notch, they are also preferred for many wall or ceiling applications.
V-notch trowels are also easier to handle than square-notch trowels because they are moving and extruding less thinset mortar. V-notch trowels with soft, plastic handles are recommended to make them easier to hold.
Square-notch trowels often have three numbers indicating the size and spacing of the notches. The first number is the width of each tooth; the second is the spacing between teeth; the third is the depth of the teeth. If only two numbers are given, the first indicates the width of the teeth and the spacing which will be the same , and the second is the tooth depth. V-notch trowels typically have two numbers. The first number is the width of the notches. The second number is the depth of the notches.
Choose a notch size based on the tile and the installation location. Your tile supplier can recommend an appropriate size for your project. The best way to confirm that you have the correct notch size is to install a few tiles, then lift them and see how much mortar contacts the tile and the underlying surface—known as the coverage. Tile in dry locations should have at least percent coverage.
In wet locations, tiles need at least percent coverage. This means that no more than percent or 5-percent, respectively, of the tile, should be dry without mortar. If doing this results in say a 6mm space between the tile in the opposite corner, it means the tile is cupped by 3mm. You must add this amount to the minimum amount of adhesive you require beneath the tile in order to get proper coverage. Visual inspection is exactly what it sounds like — you simply full embed the tile into the adhesive, removing it and then have a look at both the substrate and the back of the tile to determine whether the resulting coverage is sufficient.
The tile pictured above was pushed down only about halfway into the bed of adhesive. Notice the bed created using a 12mm square notched trowel left provides the most coverage with the bed produced using an 8mm square notched trowel right in a close second. The u-notch bed in the centre has even coverage, but note that a much larger notch is required to get the same level of coverage as the other two examples.
To achieve proper coverage you need to use the right sized trowel. You can check whether the trowel used has provided the requisite level of coverage by installing the tile as normal, pressing it down into the adhesive, then pulling the tile up and checking the back.
There should no longer be any trowel lines and you will see complete coverage of adhesive on both the back of the tile and the substrate. A 6mm x 10mm square-notched trowel for example will leave 6mm wide by 10mm high ridges of adhesive on the substrate with 6mm spaces between each ridge , whereas a square-notched trowel with the same size notch and teeth i. Fully embedding the tile into the adhesive bed will cause the ridges of adhesive to spread evenly into the spaces between the trowel lines.
Since the spaces between the ridges have the same size as the ridges themselves, this will split the height of the ridges in half. So a 12mm x 12mm trowel will leave a 6mm high bed of adhesive beneath the tile, a 10mm x 10mm trowel will leave a 5mm bed of adhesive beneath the tile and so on and so forth. Finding the right trowel for the job is quite simple when you know that, generally speaking, the trowel size should match up to the tile size — the smaller the tile, the smaller the trowel; the larger the tile, the larger the trowel.
The other main consideration is where the tiles will be set, on the floor or on the walls and ceilings. When setting tiles on the floor, the mortar bed needs to be a bit thicker to withstand the punishment of foot traffic. Another consideration is how flat your surface is.
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