I would venture to say most of you feel as I always have, that there is no such thing as a job at 70 degrees and 50% relative humidity, which are the typical published levels given for things such as drying time. It is assumed by the technical minds that develop products the average installer understands this and compensates accordingly. Why 70 degrees and 50% relative humidity? To establish basic performance levels for testing purposes. Under the American Society of Testing of Materials (ASTM) there are very specific parameters established for materials and methods used in testing to verify performance properties. This allows you to effectively shop for comparable products knowing they have all been tested under the same temperature and humidity. The published parameter under standards is actually 70-77degrees F and 45-55% RH, or relative humidity. Like products tested at higher or lower levels of temperature and humidity would likely have different values. At extreme variations they would be greatly different.
So just what happens when an installation falls outside the range as above? With cement, which is only one ingredient of many in cement based setting materials, the answer is relatively simple. For every 18 degree temperature change below 70degrees F there is a 100% decrease in the minimum cure time. For every 18 degrees above there is also a 100 % increase. This is not just air temperature; this is both ambient and surface temperature. In general, cement based products should not be used when the temperature is lower than 50 degrees or higher than 95 degrees. That eliminates tile work quite a bit of the work year doesn’t it? That is where specialty products come into play. Some manufacturers make “hot mix” products to be used in higher temperature ranges. There are also thinsets that may be used in lower temperature ranges. I have heard the comment numerous times that they continue to pour concrete through-out the winter so there is no reason why you should not be able to thinset tile. The problem with that logic is the cement in concrete has a very high profile thickness, in road construction it can be from 6 to 12 inches. During the hydration process when the cement grows its crystalline structure, heat is created. With very little additional assistance this heat is able to keep the mix warm enough to properly hydrate both using and evaporating water as it develops strength. With standard thinset mortars we have a very thin profile or thickness of cement. It can be as little as 3/32 or with specialty mortars as thick as ?”. All thinset mortars, polymer/latex modified or not have additional chemicals which allow them to be used for direct bonding. It is the combination of the thin profile thickness and accompanying lack of heat it created by the addition of these other chemicals that prevent thinset from achieving bond in cold applications. At the opposite extreme, hot conditions, no cement-based product can develop good bonding ability unless moisture is present. Heat in both the substrate and ambient air will cause a rapid loss of water preventing the hydration needed for the bonding process. Anytime cement gets hot and/or dry it will rapidly stop the hydration process.
Cement itself is a simple and versatile product. Modern day chemistry used with cement bonding materials is increasingly complex. Even the most skilled and dedicated professionals are challenged to keep up with the latest developments and chemical enhancements. We now have thinsets for submerged applications, intermittent moisture applications and dry areas only. This is all quite different than formulations of years past. Basic cement is only one part of the chemical equation in thinset mortars. With the enhanced products needed and in use today there must be considerations well beyond the basic requirements of cement. The plethora of bonding products available today range from hot weather to underwater thinsets and all manner of epoxies. If you have challenging environmental conditions hot or cold, wet or dry, consult with your favorite manufacturer and he just may have a product that will make life simple, quick, and easy. Given the challenges every installer faces daily, I will take all three anytime I can get them.