I have some cracks in my existing mortar and I have received a quote to repair them. Question on temperature. Im in Southern Indiana where the daytime high is mid 40s and lows at night in the 20s right now. I thought the temp had to be above 40 to do mortar work, but the guy who provided the quote says they can work year round regardless of temps. Is it OK to proceed with this work in the winter or should I wait until Spring when the temps are warmer?