WHEN undertaking a flooring installation, the importance of selecting the most suitable flooring products is widely understood. However, the equipment and application techniques used play just as an important role. Where adhesives are to be applied by a trowel, the choice of trowel and its use when applying adhesive is fundamental to achieving a good result.
The required bond strength of adhesive is achieved when the distance between the subfloor and floorcovering is as small as possible and has the optimal amount of adhesive between them. If too little adhesive is used, it may not deliver the required bond strength.
Whereas too much adhesive can extend the drying time or fail to adequately dry and thereby reduce the bond strength. Further, excess adhesive causes indentations to appear on sheet floorcoverings, bleeding at joints, and also causes seeping through carpet floorcoverings.
Size matters: As with adhesive selection, it’s advisable to follow the manufacturer’s recommendations when it comes to application. In many cases, manufacturers advise application with a notched trowel to ensure optimum application. In this case, the size and shape of the trowel’s notches is important because it helps to control the amount of adhesive applied.
The notches permit the flow of adhesive to settle on the subfloor in the form of strips, or ridges, with gaps in between. It’s also essential to ensure the trowel’s notches are sufficiently pointed. If they’re worn, the amount of adhesive applied, and its open time, will be reduced.
Manufacturers’ advice for angling the trowel will also help control the amount of adhesive applied. For example, F Ball & Co recommends applying most of its adhesives with a trowel held at an angle of 60deg. If the angle is too shallow, that is, close to the subfloor, not enough adhesive will be used. Conversely, if the angle is too great, too much adhesive will be applied.
Avoiding imperfections: While a notched trowel, used correctly, will ensure the correct amount of adhesive is applied, it produces ridges that may show through thin floorcoverings where the adhesive is left to dry before placing the floorcovering into the adhesive, as with pressure sensitive adhesives used to install vinyl floorcoverings.
To avoid this occurrence, often termed ‘grin-through’ or ‘shadowing’, once the adhesive has dried, contractors can flatten the ridges formed by trowel application with a roller that has been pre-coated with adhesive.
In situations where floorcoverings are installed while the adhesive is still wet, the adhesive will naturally spread as the floorcovering is pressed into it. The use of a weighted roller will also help to ensure a good contact between the floorcovering and adhesive, optimising the bond strength.