Masonry construction in cold weather costs more for a handful of reasons: slowed productivity, thawing materials, temporary heat, enclosures, higher frequency of equipment repair, etc. As a general rule, masonry should not be placed if the temperature is 40 degrees and falling or less than 32 degrees and rising. Also, masonry must be protected from freezing for a minimum of 48 hours after it is laid. Mortar should be placed while at a temperature between 70 – 120 degrees. Also during cold weather, sand with high amounts of moisture will freeze. If is to be used in the mortar it must be thawed to the appropriate temperature before use. Water used for mortar mixing should be warmed to aid in obtaining and maintaining peak temperatures. A Type III (High-Early Strength) cement is also commonly used to accelerate the curing of the mortar. The masons work area (scaffold or otherwise) may require temporary enclosure with tarps or insulating blankets to keep wind, rain, and snow from constricting the proper temperatures.
The tops of the walls, particular when a cavity exists, should be kept from falling rain, snow, and ice. Most chemical accelerators (particularly the chloride based versions) can be harmful to reinforcing steel and rebar and are rarely recommended by engineers.