For most trowels used for floor-covering installations, the correct angle to hold the trowel is 45 degrees to the floor. There is a reason for this angle. First, the angle creates a bit of a hydraulic pumping action by compressing the liquid adhesive and forcing it through the notches. If you were to hold the trowel at a 90-degree angle to the subfloor, you wouldn’t get the compressing action and would just cut through the adhesive on the floor. Without the compression from the 45-degree angle placement, the adhesive may actually skip through the trowel notches and leave you with an undesirable result.

The reason for so many trowel types is that there are so many flooring types. Think about what is being installed: Everything from thin vinyl sheet to 3/4" solid hardwood flooring. Each flooring material has unique properties. For example, a thin vinyl sheet is very flexible, so you don’t want heavy trowel notches on the floor as they will show through to the surface of the vinyl (an effect called “telegraphing”). So for thin resilient flooring, we typically recommend very finely notched towels. Wood flooring, on the other hand, has a variable backing structure. Some can be smooth and others grooved or cross-cut, so you need a trowel notch that can lift and shape the adhesive in such a way that it comes into solid contact with the flooring material. Further, wood flooring is very rigid and does not bend or conform to the subfloor. Therefore you need to use a trowel notch that accommodates for subfloor flatness and still brings the adhesive into contact with the back of the flooring. Using a thin-notched trowel for this would not allow for proper adhesive transfer. The same thing is true of broadloom carpet. Typically broadloom carpet has a rough-textured backing. In order to get proper performance out of a carpet installation, you need to make sure that the adhesive gets into this texture and that is why this application includes recommended trowel notches that create high ridges. In summary, smooth-backed flooring materials are typically installed using finely notched trowels while texture-backed materials get installed with larger-notch trowels.

The answer to this question depends on what substrate you are working over. If you are installing adhesives over soft surfaces like plywood, then a trowel can last quite a while. If you are installing over a concrete or hard, abrasive surface, then a trowel may last about 2,000 square feet before the notches wear down. An installer may think that this is a good thing because his coverage will get better per gallon of adhesive, but in the end this is not a good situation as there may not be enough adhesive on the floor for proper bonding. Some trowels may last longer, but this is always something to check before getting started on any given flooring project: Make sure that your trowel is in good condition and will deliver the right amount of adhesive required for the project.

Because you will be directly touching it with an adhesive and flooring material, both of which may not function properly when in contact with a damp substrate. For example, if your goal was to install a solid vinyl sheet flooring over a damp concrete slab using a wet-lay, water-based adhesive, once you covered the adhesive with the sheet vinyl there would be nowhere for the moisture in the adhesive to absorb into; the existing moisture would remain in its liquid state and the installation would be a mess. Another example would be to install prefinished solid wood flooring using a urethane adhesive over a damp concrete slab. The urethane adhesive would cure nicely because it cures by coming into contact with moisture, but the wood flooring would absorb moisture coming from the slab and cup, warp, curl or swell – causing a nightmare of a problem. The bottom line is that there's a reason for the moisture-limits statements of adhesives and flooring materials. As such, the installer should calculate the appropriate measurements for moisture to determine if he can proceed or if he needs to do something more to isolate that moisture from the flooring installation. Learn more here: