It's not just the adhesive that makes the difference; it's where it's spread that counts. Mapei's Stephen Chase offers up some factors to consider when spreading adhesives.



During the past ten years, the $400 million floor covering adhesive industry in North America has been developing and introducing solvent-free, water-based adhesives to the installation industry. But even as these adhesives are being used more and more to install carpet, resilient, and wood floor coverings, it is important to remember that job site conditions, as well as weather and climate conditions, will affect adhesive set-up time.

While adhesive product performance will vary from company to company, as well as within a company’s own product line (e.g. economy grade vs. premium grade), manufacturing variables do not explain the performance differences noted from job-to-job and day-to-day when the same adhesive is used.

What would cause an adhesive that worked well yesterday to not work right today? A study initiated to determine how variables encountered in the field affect adhesive set-up times found a variety of causes and effects. The following six factors, and the recommendations for controlling them, can have a significant influence on set-up times.

Subfloor Porosity

The ability for a floor to absorb moisture from the adhesive is a primary factor. The less porous a floor is, the longer the set-up time. Installers can expect at least twice the set-up time when installing over non-porous floors like tile, linoleum, sealed concrete, terrazzo, and marble, as compared to porous floors such as plywood and suspended or unsealed concrete.

Installers should allow for longer adhesive open time, circulate air with fans, and decrease room humidity when installing over non-porous substrates.

Humidity

The amount of moisture in the air at a given temperature is another important factor. The relative humidity influences the rate that moisture can evaporate from the adhesive. The higher the humidity, the longer the set-up time. The Carpet and Rug Institute (CRI) recommends that, in areas where carpet is being installed, the humidity should not exceed 65%.

Installers should dehumidify the air, increase the room temperature where the installation is taking place, circulate the air, and allow for longer adhesive open time.

Floor Covering Backings

The less porous the floor covering backing is, the longer the adhesive set-up time will be. Installers should expect longer set-up times when working with synthetic backings (e.g. hot-melt, Action-Bac, and vinyl) as compared to more porous backings like jute and mineral fibrous felt.

Ideally, installers should use a floor covering with a porous backing over an existing non-porous substrate. But as this is not always possible, other methods to help control the problem include increasing the room temperature, lowering the humidity, and allowing a longer adhesive open time.

Trowel Size

That’s right, size matters. The deeper and wider the trowel notches, the greater the amount of adhesive used, thereby leading to a longer set-up time. Since an installer must use the recommended trowel for a successful installation, this variable cannot be changed. Never use less adhesive to decrease the set-up time. This will only result in loss of adhesion, or installation failure, in three to nine months.

One viable option is to select a floor covering that can be installed using a smaller trowel (e.g. 3/32-inch vs. 1/8-inch).

Adhesive Temperature

The colder the adhesive, the longer the set-up time. Set-up time was compared for an adhesive at both 40 degrees and 70 degrees Fahrenheit. The adhesive at 40 F took one hour longer to set up than did the adhesive at 70 F. In addition, the 40 F adhesive was thicker and less stable over a concrete substrate.

To avoid problems, installers should try to condition the installation site, the flooring materials, and the adhesive at 70 F.

Open Time

Obviously, the amount of time that an installer has before the adhesive no longer transfers to the floor covering backing is crucial. When installing over a non-porous backed floor covering, or when installing over a non-porous subfloor, installers need to allow the adhesive longer open time.

If the adhesive appears to have an unusually long open time, expect a long adhesive set-up time. The same variables that affect adhesive set-up time will affect open time as well.

Even though there are some variables that cannot be controlled by the installer, such as the customer’s floor covering selection, the subfloor, and recommended trowel size, many of the variables affecting adhesive set-up time can be adjusted to better suit the installation. Understanding these variables may help to explain why the same adhesive that worked yesterday did not set up the same way today.