SEALER SERIES Part 5: The Effects of Temperature on Sealer Reactivity

By Chris Sullivan – ChemSystems, Inc.

The No. 2 cause of problems when applying sealers to decorative concrete (after moisture) is temperature. Both air and surface temperature play a role, but surface temperature is typically more critical. After application, sealers undergo a chemical reaction that causes them to cure and form a film. Temperature plays a critical role in how fast or even whether this reaction occurs. The best temperature range for applying sealers is 50 to 90 degrees F. That 40-degree window is really not very big, especially when you're working outside. This is why monitoring weather conditions and looking at a thermometer should be mandatory before every sealer application. Here's what can happen if temperatures are too low or too high.


When temperatures are too cold during sealer application, a film won't form and you're left with a white, powdery residue.

Low temperature
Every sealer has a minimum film forming temperature (MFT), or the minimum temperature needed for the sealer to properly form its film, cure, and get hard. For most sealers, this temperature is around 40 to 45 F or higher. To be safe, most sealer manufacturers specify 50 F to provide a buffer zone. If the temperature is at or slightly below the MFT, the chemistry of the sealer is affected, the reaction slows down, and you get partial to no film development. Bottom line: The sealer is weak and will not hold up very long. If the temperature is really cold, film development stops altogether and all you are left with is a white powder on the surface after the carrier (solvent or water) evaporates.

High temperature
Temperature is a catalyst. As the temperature increases, so does the reactivity of the sealer. Increased reactivity decreases the working time, or pot life, of the sealer. The faster the reactivity, the less time the sealer has to wet out the surface, de-gas, and form its film. This makes it critical to get the sealer down on the concrete quickly and efficiently. As the temperature increases, the ability to roll out sealers becomes more difficult. I always recommend spraying solvent-based sealers, especially in warm conditions (see Summer Sealer Basics). A common indication that the temperature is too high is the formation of fine "spider webs" or "cotton candy" strings coming off the roller or spray tip. This occurs when higher temperatures cause the solvent to flash before the resin (plastic) in the sealer can form its film. The pressure from the sprayer or friction from the roller pulls the soft plastic into long, thin strands.

Another common issue caused by higher temperatures is the formation of bubbles or blisters in the sealer. They occur when the solvent flashes too fast, trapping gas and air in the sealer. With today's tightening VOC requirements (see Does the Voc Content of the Sealer You're Using Meet Current Federal and Local Regulations?) more fast-flashing solvents are being used, which makes the window of application even smaller. When outside temperatures are expected to rise above the recommended application range, apply the sealer during the cooler times of the day, typically mornings and evenings.

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Chris Sullivan

Author Chris Sullivan, ConcreteNetwork.com technical expert and vice president of sales and marketing for ChemSystems Inc.

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