An article on the different types and sizes of RUBI trowels and a short description on how to choose the right one.
Probably every tiler has found himself in a situation where he couldn’t decide between two or more tools and wondered which one would be the most suitable for him. After last week’s article on RUBI cutting wheels, today we’ll talk more about another important accessory for tilers. We’ll talk about trowels, their dimensions and applying glue with them. This article should remind you of some basic information about glue application, make it easier to make a decision when choosing a metal trowel (the so-called toothed trowel), using RUBI trowels with different tooth shapes and sizes as an example.
The basic rules of tile installation are that the adhesive should cover at least 85% of the total area under the tile in a dry environment (most floors, fireplaces, etc.). In wet environments (showers, tub surrounds, etc.), a minimum of 95% of the total area should be covered. Additionally, the adhesive should overlap all four corners of the tile. Checking the correct application of the adhesive is quite easy after the tile has been peeled off. There should be no visible strips of adhesive on the underside of the tile and it should completely cover the back of the tile and the substrate.
We can certainly agree that there is no one-size-fits-all type of trowel and no one-size-fits-all size of tines for adhesive application. Its shape and size should depend on the type of tiles you will be gluing, as well as the properties of the adhesive and the substrate. The adhesive applied should be “just right” for a firm and durable bond to the tile.
Smoothers and their dimensions
The shape, size (dimension) and tooth spacing of the trowel are the basic parameters of each trowel designed for adhesive application. They let you know how much adhesive will remain on the substrate after it has been spread and also after the tile has been laid.
RUBI produces trowels for tile setters in two basic ranges: square-toothed and U-shaped. They differ in the width of the projections (gap between the teeth) and the height of the projections.
Square trowel
The 12×12 mm square protrusion smoother will leave 12 mm high glue strips with a 12 mm gap between them. If you use a trowel with 6×10 mm projections, this means that the glue strips will be 6 mm wide and 10 mm high, with a 6 mm gap between them. If only one dimension is given for a trowel, this means that both dimensions are the same (e.g. a trowel with 12 mm projections).
Smoother with U teeth
Smoothers with U-teeth normally have only one dimension listed. The dimension expresses both the width and the height of the tooth. If you use a U-tooth trowel with a 10 mm dimension, it will have crescent-shaped protrusions and the spread adhesive will be applied to the substrate in semicircular strips. The height of the strips and the gap between them will be 10 mm, i.e. with the dimension indicated on the trowel. The width of each strip will be double the dimension indicated on the trowel.
How much adhesive does the trowel leave under the tile?
The size of the trowel teeth determines how much adhesive is left on the substrate, more precisely how thick the adhesive bed under the tile will be. If you use a 12×12 mm square tooth trowel, the adhesive bed under the tile will be half the thickness of that dimension, i.e. 6 mm. A 6×6 mm trowel will create a bed 3 mm high, as the adhesive will also spread into the space between the strips formed.
Smoothers with U-shaped teeth will leave an adhesive bed approximately 1/3 the height of the teeth. So the bed height for a 10 mm trowel will be approximately 3 mm.
Which trowel to choose? With square or U teeth?
U-tooth trowels from 10 mm and square trowels from 6 mm leave a minimum 3 mm adhesive layer under the tile. So which one to choose?
The shape of the teeth determines how easily the adhesive is spread and how perfectly the tile is set into the adhesive. In general, it is easier to set a tile in adhesive prepared with a U-tooth trowel because semicircular strips of adhesive are easier to spread than square ones. Square strips of adhesive must be spread on both sides when the tile is pressed. The top of the strips are pressed out first and then the sides are pressed out. When the tiles are pressed into the semicircular strips, the adhesive will spread on the underside with less chance of air bubbles forming.
How to choose the right trowel?
Determining the correct trowel dimension (size) depends on the tile itself and the substrate. More specifically, it depends on how flat the tile and substrate are. The curvier the tile or substrate, the more adhesive you need, which also means using a larger size trowel.
First, you need to determine how much adhesive you want to have underneath the tile after it’s glued down. The minimum thickness should be 2 mm. Choosing a minimum adhesive thickness of 3 mm will make it easier for you to calculate the correct trowel size. There are two basic ways you can determine the correct trowel size: calculating the deformation of the tile and the substrate or visual inspection.
Calculation of deformation
Calculating the deformation of a tile means determining the amount of deviation from the plane. You can calculate it by laying one tile on top of another and comparing how the corners fit together. If the tile is curved, the opposite corner will be deflected. Measure the size of the gap between the corners of the tiles and divide the value by two. The result gives you the deformation of the tile.
One example, if when comparing tiles a gap of 6 mm is created in the opposite corner, this means that the tile is 3 mm crooked. You need to increase the intended thickness of the adhesive layer you want under the tile by that many mm to get the correct thickness of adhesive! If you want the adhesive layer under the tile to be a minimum of 3mm and the tile has a 3mm warpage, you need to use a trowel to create a 6mm thick layer of adhesive. In this case, you will achieve proper coverage with a 12 mm square-toothed trowel.
Visual inspection
Visual inspection is done simply by placing the tile in a layer of adhesive. You then take it out and look at the substrate and the back of the tile to check that you have the correct adhesive coverage.
You can see an example in the picture. This tile has been pushed into the glue about halfway. Note that the adhesive bed created by the trowel with the 12 mm square teeth on the left side has the most coverage. The bed formed with 8 mm square teeth follows behind. The smoother with the U-tooth in the middle does have even coverage, but you would need much larger teeth to get better coverage.
When using the tile deflection calculation method to determine the correct trowel size, you must still also visually check the adhesive coverage to make sure you are using the correct trowel size!
Do not forget the main principles
In general, the larger the tile, the larger the size of the trowel used. It is always better to use a larger dimension than you would actually need. A little more adhesive under the tiles is perfectly permissible, while an insufficient amount of adhesive is unacceptable.
The use of a trowel with square or U-shaped teeth is a personal choice of the tiler. Although it is easier to achieve the desired adhesive coverage using U teeth, you must use a larger trowel tooth size to achieve the same thickness of adhesive bed. But with vertical tiling, this is sometimes more difficult because an adhesive bed created with smaller square teeth is more likely to last on the wall than one created with larger U teeth.
We have briefly explained what types of trowels you can use for tiling, how to choose the right size of trowel and its teeth to make the tiling process well done, durable and time-efficient at the same time. Of course, it also depends a lot on the materials used, the quality of the tiles, the adhesive used, the mixer, the levelling system, the various accessories and, last but not least, your skill and experience.
This article was written in collaboration with www.profiobkladac.sk.