Trying Drying Times Ahead
November 29, 2007
By now most of the country has been blessed with the first cold snap and the start of rain and/or snowy season. For those of you blessed (I think) to live in warmer year around climates it is hard to grasp the challenges of winter weather when it comes to floor covering products. All flooring products present their respective challenges when chilled. The vinyl is hard, the carpet is stiff, the wood is cold and dry, and the tile is just plain cold. Until about this time of year we could load up our vehicles the night before and leave our adhesives and setting materials in the truck ready for work the next day with minimal downtime getting to the job. Now, as cold sets in we start a new life, loading and unloading daily many of the tools and products we may need to use the next day each night so they are warm and ready. All this assumes the next day we will have a nicely acclimated jobsite with acclimated materials waiting to be installed. Therein lies the problem and focus of this article.
The reality is we did not leave our products at the job because the structure is often not secure. Even if we did have that luxury, the heating guy won’t be there for two more weeks because the electrician still has not hooked up the power. Is acclimating structures and products vastly overrated? On each and every job, the conditions and circumstances vary, making an exact response challenging. If the question is, whether lack of acclimation will impact the installation in some manner, the answer is soundly, YES. You could easily fill the space of half this issue with all of the “if” scenarios. We will attempt to focus on some of the more common issues typically seen.
Let us first deal with the famous initial drying time of X hours at 70 degrees Fahrenheit and 50% relative humidity. Why 70 degrees? It would be quite feasible to rate products at 60° or 80° but for consistency in performance testing and installation recommendations, the range used for tile setting products and materials is 70°-77° and 45-55% relative humidity in most instances. If the air is warmer, the time will be less, if colder, it will be more. Roughly speaking, for each 18° temperature change there is a 50% increase or decrease in drying times. This includes air temperature, surface temperature, and product temperature. If the temperature goes below 50°, cement based thinset products typically may not reach initial cure. The argument to this usually goes like “if they can pour roads in the winter, you can use thinset, cement is cement”. Not true; you can use additives in concrete that you can not use in thinsets. Also natural cement hydration causes a heat build-up. With a 4 or 6” slab or a 10” road you have much greater mass generating heat. The heat generated by a thin cement profile of 3/32” to a 1/2” does not allow for the heat build-up possible in slabs by simple lack of mass. And, if all that were not true, thinsets use a wetting agent which is what allows the product to be used in a thin profile but this retarder also contributes the reason it will not dry in cold weather, it is the opposite of an accelerator typically used in concrete. So, what does all this mean to the installer? You really need regular permanent heat installed to make the best of an installation.
Temporary heat may appear to solve a problem by raising the air temperature but rarely does it run long enough to raise the surface temperatures. Another problem that occurs with temporary heat is cement carbonization which is caused by a chemical reaction. Any heater burning a fossil fuel produces CO2 that will combine with calcium hydroxide in fresh cement based products which in turn forms a weak layer of calcium carbonate interfering with cement hydration. The result is a soft, chalky material that has little if any bonding ability. Depth and degree of carbonation depend on concentration of CO2, curing temperature, humidity and type of thinset. It is not uncommon to have this condition “kill” a slab in winter construction. By kill, we mean the surface is completely powdered and incapable of being bonded to. This chemical reaction occurs at a level well below that which would pose a danger to the human respiratory system. If chemical reactions and the risk of getting gassed is not enough reason not to use temporary heat, consider the vast amount of moisture an unvented heater releases in the air. When you’re trying to dry out a product that must evaporate water vapor it is self defeating to pump more water vapor in the air. Both carbon monoxide and carbon dioxide can also be serious health threats. The accompanying side bar article explains the difference and the health risks of each condition. For this and many other reasons, direct-fired temporary heaters are a poor choice to heat structures for tile installations or any other type of flooring installation.
The last concern we will address is changing moisture levels. Anyone who has been in the flooring business a while knows that with exception to gross instances of installation shortcomings, most problems are not readily apparent till after the structure cycles a few times, meaning a few years of acclimation. If a house is cold and dry, we can count on expansion such as subfloor panel seam peaking wrecking havoc with any flooring material including ceramic and stone products. Conversely, if the structure is damp and warm there will be contraction as framing members and floor panels dry out and return to their natural size. We understand the real world and don’t expect any one article will change the way one does business in the ever shrinking and competitive market conditions that currently exist. But, we do hope to renew and reinforce your concerns that less than ideal situations often result in less than desirable outcomes. The risk in using temporary heat is not only to the installation, but your health as well so work smart and work safe.