#MAPEITechTip: Is Trowel & Adhesive Selection Important When Applying a Floor Covering?

Just how much Floor Covering Adhesive is too much or too little?  Using the ‘right trowel & right adhesive’ combination is the key to a well-bonded floor covering to the substrate that will perform during the ‘service life’ of the installation—avoiding costly repairs or callbacks.  When the right trowel is selected the proper amount of adhesive will be applied consistently to substrate regardless of the size of job—from a residential 1,000sq/ft installation to 10,000sq/ft. commercial project.

Just as important as surface preparation is to a successful installation, selecting a high-quality adhesive that has been specifically formulated for the appropriate substrate, floor covering backing and service conditions.  That is why it is always key to start with the manufacturer of the floor covering for specific recommendations and limitations before installing their flooring.  Some manufacturer’s have specific adhesives along with trowel recommendations that must be adhered to ensure proper adhesion to the substrate in line with their warranty.  This is becoming even more important as many floor covering and adhesive manufacturers are formulating products that are more ‘sustainable’, meaning that they are lower in VOCs and don’t contain materials on the ‘LBC (Living Building Challenge) Red List’—which often means that installers must modify their application techniques to accommodate non-solvent based flooring and adhesives. 
 
This makes selecting the trowel profile and size (V-notched, U-notched or square-notched, ie: 1/32” x 1/16” x 1/32”) even more important with today’s floor coverings and adhesives—to use a trowel that is recommended by the floor covering or adhesive manufacturer. Since the width and depth of the notch act as a gauge for applying a consistent amount of adhesive, notches that are too close together can result in insufficient coverage, resulting in a shorter open time and poor bond performance. Notches that are too far apart can result in ridges showing through the flooring product.  To ensure proper adhesion, we might be inclined to add more adhesive than recommended, thinking more is better, when in reality its not.  Too much adhesive will take longer to dry and can result in bubbles, ridges and indentations caused by point loads applied before and after the adhesive fully cures. This will ultimately weaken the flooring system, greatly increasing risk of installation failure.  While the converse is also true, not applying enough adhesive will not only shorten open time, but also increase the risk of inadequate contact between the adhesive and flooring material–resulting in a weak bond. That is why it is imperative, in addition to selecting the right adhesive, and selecting the correct trowel for the job, to replace worn out trowels.  Worn down notches can result in minimal adhesive application, on larger jobs this may require changing out the trowel frequently to ensure a consistent adhesive bond is maintained. Employing good installation practices will aid in achieving a good bond between the floor covering and the substrate—cleanliness of the trowel and knowing when to replace it.  If trowel notches become clogged with dried or gummed up adhesive, it can interfere with proper adhesive transfer to the substrate.  

While we might take the trowel and adhesive for granted, it really can make the difference between success and failure on our project!