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.

Open time, sometimes called flash time, describes the amount of time that we want the freshly troweled adhesive to remain open to the elements before you start installing floor covering. There is a good reason why open time needs to be followed: Many water-based adhesives need a little time to start evaporating and letting some of the water out before you start installing flooring. Moisture-curing adhesives need to be exposed to atmospheric humidity to get the reaction started. Again, if you start installing before allowing for the recommended open or flash time, you run the risk of a delayed curing time, which can lead to placement problems and long-term performance issues.

This term refers to the amount of time, after the open time or flash time (if any), during which the adhesive you just applied will accept the flooring material and still provide an adequate bond. If you leave certain adhesives open to the atmosphere for too long, they will skin over or cure out and not be wet/sticky enough to accept the flooring material. In other words they will dry out. It is important to note that working time is often affected by the ambient temperature as well as the ambient humidity. For example, in arid parts of the country when the temperature is very high, working times will be much shorter for water-based materials but much longer for moisture-curing materials. Areas of high humidity and high temperature will have longer working times for water-based materials but potentially shorter working times for moisture-curing products. Cold temperatures are going to slow everything down whether the products be water-based or moisture-curing. For reactive adhesives like epoxies or epoxy-modified polyurethanes, temperatures will greatly affect the working time. Reactive adhesives are very sensitive to temperature, so cold conditions will extend the working time and hot conditions will speed things up.

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:

Excess moisture in a plywood or wood substrate is a probably just as damaging to a floor installation as high moisture content in a concrete slab. According to industry standards, the moisture content of a plywood substrate should be in the range of 10% to 15%. Dryer than that risks extreme adhesive absorption and subsequently poor adhesive transfer to the flooring. Wetter than that (such as through exposure to rain before installation) and the adhesives will take longer to dry; then when you have installed the flooring and the plywood has dried out, you will see the result of the plywood panel shrinkage through the surface of the flooring. A critical success factor for any floor installation is to make sure that the substrate you are working on is stable and acclimated to the working environment. Anytime you step outside that playing field, you will find yourself in trouble.

Traditional OSB is a problem for resilient and wood flooring installations because of the nature of its construction. Traditional OSB is made from large chips of wood that will swell when exposed to humidity and moisture, causing the texture of the chip structure to show through on resilient floors. According to the Engineered Wood Association, OSB is only suitable as a substrate for stretch-in carpet, which isolates the texture of the OSB from the flooring with a layer of carpet pad. The association goes on to recommend applying a 1/4" layer of underlayment over the OSB for installation of resilient and wood flooring. The main thing to remember about traditional OSB is that it is very absorptive and swells when exposed to moisture (such as rain). This swelling is not good for floor installation. Having said that, there are new OSB products out there that are “engineered” materials, making them different from traditional chip/strand OSB. Some of these new engineered OSB boards have much better moisture resistance and can handle water contact without a change in dimensional properties.