Why would the multipurpose carpet adhesive that worked well yesterday on one job site appear to have different characteristics today on a different job site? What factors affect the way an adhesive sets up? There are a variety of conditions, such as the substrate temperature and porosity, ambient temperature, relative humidity, trowel size, etc., that will affect how an adhesive reacts on any given job site. The intent of this article is to look at these various conditions and find a way of work around them.
Substrate Porosity:
A non-porous substrate, such as a concrete floor with a highly polished steel trowel finish, will not absorb the moisture of the adhesive as readily as a porous substrate or as a self-leveling underlayment.
The Remedy : After spreading the adhesive, allow the adhesive longer open time to develop tack. Be very cautious about increasing air circulation since this may cause the adhesive to flash off too fast and result in the adhesive skinning over.
Temperature:
Substrate, ambient and material temperature will affect the working characteristics of the adhesive. Obviously, if the temperatures of either the substrate, air, flooring covering or adhesive are cooler than normal room temperature, or below 10°C, the adhesive will take much longer to set up and develop tack.
The Remedy: Pretty obvious. Get some heat into that space and try to raise the temperature of the substrate. Once the ambient and substrate temperatures are raised to proper working conditions, deliver the floor covering materials and adhesive to the job site and acclimate all the materials to room temperature.
If ambient and substrate temperatures are higher than normal, above 30°C, the adhesive will flash off too fast and skin over. This will result in very poor or no adhesion.
The Remedy: Turn off the heating system and allow the ambient and substrate temperatures to return to normal room temperature. Turn off radiant floor heating systems 48 hours before the installation begins and do not turn these systems back on for 48 to 72 hours after the installation is complete. Use indirect auxiliary heaters to maintain the temperature in the area to the recommended workable level.
Relative Humidity:
The relative humidity, or the amount of moisture in the air, affects the rate or speed by which the moisture in the adhesive can evaporate. The higher the humidity, the longer it will take for the adhesive to set up. The flooring industry recommends the relative humidity not exceed 65% when installing floorcovering materials. If the relative humidity is 75% – 90%, it may take twice as long for the adhesive to set up and develop tack compared to when the relative humidity is 25%.
The Remedy: If the relative humidity is too high, increase the room temperature and air circulation. Run a dehumidifier in the area to reduce the amount of moisture in the air. Allow the spread adhesive more open time to develop tack.
Trowel Size:
The same adhesive may be used for two different backings. However, a smaller notched trowel may be recommended for a smooth backing, where as a larger notched trowel may be recommended for a heavily textured backing. Since installers must use the recommended trowel size for a successful installation, this variable cannot change.
The Remedy: Allow an appropriate amount of open time for the spread adhesive to develop good tack. Do not use less adhesive to speed up the set up time of the adhesive. This will result in an installation failure.
So, if you get caught on a job site with a highly polished steel trowel finished on-grade concrete slab and the substrate temperature is 10°C with an ambient temperature of 10°C and relative humidity of 90%, don’t be too surprised if you have to wait 2 to 3 hours for your “economical” adhesive to set up. The remedy for this typical situation is simple. Get heat and air circulation into this area and use high-solids, fast-grab adhesive.
Understanding the variety of job conditions and how these individually, as well as collectively, affect adhesive characteristics may help explain why the same adhesive that worked well on one job site yesterday did not work the same way today.
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