Why is low temperature flexibility of your roof coating system important? Because a roof coating system needs to be able to expand and contract with the substrate without cracking. If it cracks it will ultimately fail. In the summer time when temperatures are in the 70’s and 80’s this is easy to do. In frigid temperature below zero – not so much.
As has always been the case the variability of the weather is a given. Extremely cold temperatures occur in different places throughout the country and at different times throughout the years. In fact every state in the union except for Hawaii has experienced temperatures below zero at one time or another. So, the low temperature flexibility of your elastomeric coating system should be a consideration no matter where you are. Obviously, it is more important in the northern tier and mountainous areas of the country where extremely low temperatures are more likely to be encountered. But -2˚F in Florida certainly qualifies as a low temperature.
Standards for Low Temperature Flexibility
Elastomeric Roof coatings are formulated with specialized features to provide long term performance. One feature is low temperature flexibility. ASTM 6083 Standard Specification for Liquid-Applied Acrylic Coating Used in Roofing specifies that the product shall be able to pass a ½ Mandrel Bend @ -15˚F after accelerated weathering. This is evaluated using test method ASTM D 522 Method B. The results required for this test and the others specified in ASTM 6083 are relatively easy to achieve. ASTM 6083 was updated in 2021 and was somewhat diluted from its original version. While it does set the bar, Acrymax chooses to raise the bar and engineer all of our elastomeric roof coatings to exceed ASTM 6083 requirements.
When selecting the appropriate polymers to use in formulating our roof coatings we pay particular attention to the Glass Transition Temperature Tg is This temperature is the temperature at which a polymer turns from a flexible material to a harder more brittle material. From a rubbery to glassy state. Hardness, brittleness, and other properties including thermal expansion coefficients are all affected. The polymers we use in our coating formulations have a Tg of -35˚to – 40˚F.
The introduction of a plasticizer reduces the glass transition temperature, Tg, of the material which permits the polymer to remain more flexible at lower temperatures. Unfortunately, plasticizers migrate out of a coating or membrane over time and the Tg rises accordingly.
Acrymax utilizes only 100% Acrylic polymers that are engineered to remain flexible at low temperatures without the use of external plasticizers. The polymer is inherently flexible.
Effects of weathering on low temperature flexibility
Weathering affects the properties of all polymers. Degradation is inevitable. The severity of the effect of weathering will be impacted by the polymer chosen and how that polymer is formulated. As mentioned above plasticizer migration is a problem.
In a presentation to the International Conference On Durability of Building Materials and Components regarding testing of single ply roofing the following was stated “data show the glass transition temperature gets higher for many of the membranes as they weather. The TPO, PVCs, and BURs show linear increases of approximately 1˚C per year. At this time, age causes little change in the glass transition point of the other membranes.” 1
If one accepts a 1˚C or 1.8˚F per year linear increase in the Tg this equates to a 36˚ F change in the Tg over the 20 years many of these membranes are warranted for. An increase in the Tg of this magnitude will make them less capable of withstanding thermal shock and cold temperatures as they age and could lead to their ultimate failure.
Low temperature flexibility is but one of the properties required of a high quality roof coating system, but its importance should not be underestimated. A crack in a coating caused by its inability to expand or contract with the substrate will create a weak point in the system that will lead to failure. Bear in mind that a crack that occurs when it is extremely cold will not repair itself when the roof returns to more normal temperatures. The damage will have been done.
Acrymax offers elastomeric roof coating formulations engineered for a variety of specific purposes and end uses. All of these coatings feature excellent low temperature flexibility and they maintain that flexibility over time.1 International Conference On Durability of Building Materials and Components LYON [France] 17-20 April 2005 Predictive Service Life Tests for Roofing Membranes