Well, it depends on the sealer. If you are applying a sealer to a concrete driveway that requires 24 hours to dry, it could freeze or harden within the pores. Foundation Armor manufactures a lithium silicate based sealer, the Armor L3000, that takes only 6 hours to dry. As long as the temperature outside is above freezing point, the sealer will be able to react before having a chance to freeze. Further, the Armor L3000 works below the surface so you don’t have to worry about the sealer freezing on a surface level. The Armor L3000 also has to be diluted with warm water. The temperature of the water is enough to warm the concrete just enough to allow for an immediate chemical reaction.