Masonry Magazine January 1975 Page.19
In cold weather masonry construction, mortar admixtures such as anti-freezes, accelerators, corrosion inhibitors, coloring agents, and air-entraining agents are often encountered. Most of the commercially available "antifreeze" mixtures for mortar are misidentified. They are accelerators rather than mortar freezing point depressants. Some actual antifreeze admixtures, including several types of alcohol, are available. If used in quantities that will significantly lower the freezing point of mortar, the compressive and bond strengths of the masonry may decrease rapidly. Since antifreeze compounds have little benefit, they are not recommended.
The primary purpose of an accelerator is to hasten the hydration of the portland cement in the mortar. Calcium chloride is the most commonly used accelerator. It is also the main ingredient in most proprietary cold weather admixtures. Although calcium chloride is an effective accelerator, it may produce undesirable side effects such as corrosion failures of joint reinforcement, door bucks, metal ties and anchors in masonry. Also, excessive salts can contribute to efflorescence and may cause masonry spalling. Accordingly, calcium chloride should not be permitted in masonry containing metal ties, anchors and reinforcement. If used, it is recommended that it be limited to amounts not to exceed 2% of the portland cement and 1% of the masonry cement, by weight. The effects of commercial accelerators containing corrosion inhibitors on masonry and cold weather masonry construction has not been evaluated. Consequently, the use of such accelerators cannot be recommended.
Material Storage
All masonry units, when delivered to the job site, must be carefully stored. Masonry sand, when bulk delivered, should be covered to prevent the entrance of water from rain or melted snow. Consideration should be given to methods of stockpiling of the masonry sand that permit heating when lower temperatures warrant this construction practice. Bagged materials and masonry units, when delivered to the construction site, should be stored elevated to prevent moisture migration from the ground to the materials, and then protected against water penetration through the sides and top.
Coverings should be properly installed so that all materials are completely covered. Tarpaulins, reinforced paper, polyethylene or other water-repellent sheet materials may be used. If the weather and size of the project warrant, it is recommended that a shelter be provided for the materials storage and mortar mixing areas.
Materials
Heating
The mixing water is the most logical masonry material to be heated. Heating only the water will be satisfactory if the other construction materials are unfrozen. (Water may be heated using a 55-gallon drum with a fire or heat source below, or with immersion heaters, flame guns, or steam probes.) Any method that does not add deleterious matter to the water is acceptable. The mixing water should be heated sufficiently to produce mortar temperatures between 40 F and 120 F. Once a mortar temperature has been selected in this range, every effort should be made to maintain this temperature for consecutive batches.
Masonry sand should be heated when the temperature of the sand is below freezing (32 F). A simple method for heating sand for mortar is to heap sand over a section of a large diameter metal pipe (such as a culvert or smokestack) in which a slow-burning fire is built. Any device that allows the thawing of the ice without scorching the sand is satisfactory. Whenever wood fires are used for heating the sand, care should be taken to prevent the wood ash from contaminating the sand and mortar.
When the temperature of dry masonry units is below 20 F they should be heated so they are above 20 F at their time of use. Wet frozen masonry units should be thawed without overheating. These heating requirements prevent rapid cooling of the heated mortar as it comes into contact with the masonry unit. Even when the temperature is above 20 F it may be advantageous to heat the units for greater mason productivity.
Protection
General
An enclosed construction site maintained at the normal temperature (greater than 40 F) would be ideal for all cold weather construction. Economics, however, dictates how elaborate the protection can be, whereas ambient temperature dictates when the protection is needed or when work stoppage should be enacted. A balance of mason productivity and structure protection with economics is required. Because each case is different, specific procedures should be designed for each particular job. The range of protection may go from a simple windbreak to a completely enclosed structure.
Types
Enclosures and windbreaks are temporary and therefore are designed to fit the particular job. They can range in size from a single insulation blanket to an elaborate shelter which protects the entire work area.
Materials commonly used for protection are canvas and synthetic coverings (reinforced polyethylene and vinyl). The ingenuity of the individual contractor sometimes is exhibited by the use of other materials for protection. Such characteristics as strength, durability, flexibility, transparency, fire resistance, and ease of installation should be considered when selecting protection material. In most instances, an unheated enclosure reduces the chill factor (temperature plus wind), and provides the degree of protection that is adequate for most masonry construction.
Scaffolding should be properly erected, braced and anchored, so that the assemblage is safe from snow and wind loads and lift.
Safety
The protection should provide measures to safeguard the worker from injuries caused by high winds, fires and air contamination. The enclosure, heated or unheated, should protect the structure from early freezing, and if heat is applied, from rapid mortar dry-out.