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.