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MAPEI Tech Talk is a blog devoted to the flooring and construction industry. It is updated on a regular basis by the social media team at MAPEI Americas, and it will feature guest bloggers occasionally as we provide you with viewpoints from across the industry.
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Shawn is a Regional Technical Representative at MAPEI Inc. and is based at its Delta, British Columbia, facility. He provides technical assistance, training and general advice on all of MAPEI’s product lines to users across western Canada.
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February 5, 2018 - 19.12
Adhesive Terminology in a nut shell - Part Two -
by Shawn Millman
Today I am continuing on from where I left off, in my previous post about adhesive types and definitions. I welcome you to go back and give it a read if you haven’t already by clicking here. Otherwise, read on for more interesting clarifications and review of our industry’s oft-used words.
Pressure sensitive adhesives (PSAs) were already discussed in the first edition of this article, but there is a little more to say. To recap, pressure sensitive adhesives are allowed to stand on the substrate until it becomes dry to the touch. Pressure applied on top of the flooring after it makes contact with the glue ensures that the bond is established. However, not all pressure sensitive adhesives are the same!

Many PSAs make for a permanent bond between the glue and the floor covering on top of it. Installing a modular format floor such as vinyl tile, VCT, luxury vinyl tile/plank on top of these adhesives is a breeze. They are especially easy to deal with when compared to wet-set installation method, as the flooring product will stay in position after applied, and the installer is able to work on top of the floor as it goes down with fewer precautions taken.
Permanent bond comes with a catch though.  In areas where a floor needs to be repaired or otherwise removed for any reason, the flooring material and substrate will most likely be damaged in the process.  To ease the cost, hassle, and turnaround time for projects where flooring needs to be removed occasionally, it is best to use a releasable adhesive.  While releasable adhesive looks and functions the same way as traditional PSAs do, a suitable flooring product will facilitate removal and replacement when installed on a releasable adhesive.  It must be emphasized that for releasable installations, the manufacturer of the floor covering product should recommend that their product can be installed in such a way.  Releasable adhesives have always been associated with carpet tile in particular, but manufacturers may provide other releasable floor covering options such as luxury vinyl plank. 

These next few points are somewhat basic, but still worth reviewing.  The terms open time, flash time, and working time shouldn’t generate too much confusion, but they do nonetheless.  Take care to understand what adhesive type you have, and no matter what manufacturer’s adhesive you use, it will make perfect sense.
Wet-set adhesive is perfect for demonstrating what I mean.  Here, the adhesive will have an open time or a working time defined in its instructions.  In either case, the adhesive must receive flooring on top of it before the adhesive dries.  The working or open time expressed in the instructions is basically a limit, by which time the adhesive must be covered.  With MAPEI’s transitional-set and pressure sensitive adhesives, some amount of initial drying delay called flash time, is always required.  Failure to allow these adhesives to undergo some evaporation (or flashing off) can result in flooring defects, and improper cure of the adhesive which can lead to flooring failure.  The flash time of a PSA will be complete when the adhesive is dry and tacky to the touch.  The flash time of a transitional-set adhesive is just the amount of time that is needed for the adhesive to develop wet tackiness.  Also known as wet tack or a wet tacky state, the adhesive can be dry and slightly tacky to the touch, yet able to be smudged around and have fairly wet adhesive within the trowel ridges.

Last but not least, is working time; with PSA and transitional-set adhesive, there is a maximum amount of time that the adhesive can be open to the air.  Working time begins at the point in time when adhesive is spread on to the floor.  The installer is not meant to think of working time as being added time, after the period of flash time that is allotted.  See the excerpt below from the data sheet of a PSA, MAPEI’s Ultrabond Eco 350.
Version: July 27, 2015 (always visit www.mapei.com for the latest product data sheets)
Try to keep in mind that substrate porosity, ambient relative humidity, and temperature all have a significant effect on these parameters.  The figures given in technical data sheets are assuming “middle of the road”, acceptable conditions that are common to interior spaces that are enclosed with HVAC systems operational.  The default conditions are generally close to 23 degrees Celsius and 50% relative humidity.  I hope that this post has been of some interest to you, and always, thank you for reading.
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