A quick look at the last 50 years shows wide-ranging changes in floor covering adhesives. We can fast forward through all the solvent-based adhesive history as that chemistry base, for the most part, is completely gone and there are only a few of us who still remember what it was like to use them. In more recent times, felt-back sheet vinyl and broadloom carpet were the rage and most flooring or adhesive manufacturers were risking it all at 3lbs moisture vapor emission rates when tested according to ASTM F-1896. Relative humidity testing was just getting its legs in the industry and those companies progressive enough to understand its meaning started positioning installation adhesives and systems at a maximum level of 75%. So how did we get from a virtual desert of dry concrete at 3lbs MVER and 75% RH to today’s new standard of just about anything goes?
The answer to that question comes in two parts. The first part is driven by significant changes in the type of flooring being installed. It may not be fair to say, but the days of broadloom carpet and wide format rotogravure sheet vinyl seem to be long gone. A battle is being waged against those traditional flooring types by their modular cousins and the modular systems are winning. With respect to commercial carpet applications, modular carpet tile is fast becoming the product of choice for obvious reasons: Ease of transport, installation and removal make carpet tile a perfect choice for almost any commercial environment. Sheet vinyl is fast (if not completely) being replaced by luxury vinyl tile (LVT) for these same reasons. Further, LVT offers easy access to a wide variety of visuals, textures, and shapes all designed to be assembled on the job site with minimal tools and basic installation skills. The main factor influencing the decline of broadloom carpet and sheet vinyl is their size and installation complexity plus the availability of skilled craftsman to install them. This is not to say installers of carpet tile and LVT are unskilled, it is just to say that there are some very different techniques involved when dealing with a 6’-, 12’- or even 14’-width piece of flexible flooring compared to a 4” x 36” piece of LVT or an 18” square carpet tile. This change in flooring type is driving the second part of the answer as to why adhesive systems have changed so much in the past several years.
Installation methods for broadloom carpet and sheet vinyl almost always require a porous concrete (or other) substrate and a wet-lay installation method. Porosity is mandatory because there needs to be somewhere for the moisture in the adhesive to evaporate into in order to properly dry. Wet-lay installation methods are necessary because the adhesive system needs to be somewhat slippery to allow the installer to move large sheets of flooring around during the placement process. With the advent of modular flooring all that porosity and wet-lay installation requirements went out the door and a different installation technique was chosen. Welcome to the world of high-performance pressure sensitive adhesive systems designed specifically for modular flooring. It is these types of adhesives that allow for the “almost anything goes” positioning for moisture conditions.
Press & Go: Pressure Sensitive Adhesives
High-performance pressure sensitive adhesives (PSAs) have led the way in terms increasing moisture resistance when used to install modular flooring. PSAs differ in many ways from traditional broadloom carpet or felt-backed vinyl sheet flooring beginning with their basic chemistry. Traditional broadloom carpet and felt-backed vinyl sheet flooring are based on SBR (styrene butadiene rubber) latexes and offer a unique set of performance attributes that work well for carpet and felt-back sheet vinyl. They are fairly inexpensive, have leg development to hold flooring in place during cure, and dry to a fairly sticky resilient bond. What SBR adhesives do not have is plasticizer migration resistance which is absolutely required when bonding solid vinyl flooring, such as modular carpet or LVT. PSAs are typically based on acrylic latexes, which do have plasticizer migration resistance. PSAs also do not require a porous substrate on which to function and can, in fact, be used on properly prepared non-porous substrates. The trick to their ability to function at elevated moisture levels is to get them completely dry before installing flooring. If this critical step is not allowed to happen, and floor covering is installed while the adhesive still has some moisture remaining, the adhesive will not have a chance to completely coalesce and can re-emulsify resulting in a complete floor failure. This is the challenge for high-moisture-resistant pressure sensitive type adhesives. Using them on high-moisture-content concrete substrates will definitely extend their dry time. An anxious floor covering contractor may decide to push the envelope and start installing before the adhesive has completely dried and that would be a mistake. A word to the wise is to always follow the installation instructions written on any given technical data sheet to make sure you are getting optimal performance of your chosen adhesive system.
Double-sided Tape = Zero VOC
A new entry to the resilient floor installation market is in the introduction of high-performance double-sided acrylic tape systems. In all fairness, double-sided tape products have been around on the market in one form or another for many years, but it has not been until recently that the products have been developed or redesigned to meet the rigorous requirements of a high-moisture-resistant installation system for resilient flooring. The tapes that seem to be finding acceptance are based on solvent-born, acrylic pressure-sensitive adhesives applied at the factory on a mylar or plastic film. The fact that they are solvent-based means that they are applied in a solution rather than an emulsion which makes them immensely more moisture-resistant. Obviously, all the solvent is removed in the manufacturing process and what a contractor deals with on the jobsite is a true zero-VOC material. The advantage of these high-performance tape systems is that they provide instant functionality in that there is no flash time, no open time, and as long as the release liner is kept in place, have an infinite working time. The second advantage is that once flooring is installed, the room can be put back into immediate use as there is no waiting time for the adhesive to dry or cure.
Another entry into the adhesive market for resilient flooring are the modified silane polymer type adhesives. Although new to resilient flooring, this type of adhesive has been used extensively in the wood floor installation market and is a viable competitor to urethane-based adhesives. For wood adhesive installation, modified silane-based polymer adhesives offer high moisture resistance and even moisture barrier properties. They also offer easy clean up if residues are left on the surface of the wood floor and allowed to cure. Modified silane polymer adhesives are now showing up for resilient flooring offering many of the same performance attributes. Most adhesives of this type are being offered up as providing high moisture resistance along with excellent heavy rolling load resistance and superior bond strengths.
Other floor fastening systems are being promoted in the market in the form of magnetic bonding where the flooring and substrate are covered with a magnetic film and pieces held in place by magnetic forces. Some flooring manufacturers are embracing this technology with some of their more contemporary modular flooring products allowing for all sorts of creative installations both on the floor and in vertical applications as well.
And then there are those floor systems that do not require adhesive or bonding solutions of any form. These are loose-lay systems and typically go together using a proprietary click system which locks the whole floor assembly into a single piece and allows it to float over virtually any substrate.
In summary, considering the almost infinite choices of floor covering materials available, there are almost an equal number of ways to bond, or not bond, them to the subfloor. The challenge is to find the right one that matches with the requirements of the floor and substrate and to make sure it is installed according to all instructions.