Masonry contractors are frequently tempted to continue working when the weather conditions are opposed to a quality result being produced. The weather is volatile and time is money.
Concrete and mortar cure by a chemical reaction that can only take place within a range of temperatures. When the temperatures fall below freezing the work must be heated or it will not cure properly. It will be crumbly and have no strength. Conversely, too hot, past ninety-five degrees, also can pose problems. There are other factors as well.
We will not risk working on your project when the weather doesn’t permit it. Many times we use three different heaters when working in the winter, just in case one or even two fail or run out of fuel.