Quality Control All-Weather Construction

1) Cold Weather Construction
2) Hot Dry Weather Construction
3) Wet Weather Construction
4) Guide Specifications

1. Cold Weather Construction (continued)

1.1.5. Placing grout and protection of grouted masonry.

When air temperatures fall below 40 F., grout mixing water and aggregate shall be heated to produce grout temperatures between 40 F. and 120 F.

Masonry to be grouted shall be maintained above freezing during grout placement and for at least 24 hours after placement.

Where atmospheric temperatures fall below 20 F., enclosures shall be provided around the masonry during grout placement and for at least 24 hours after placement.

1.2. Admixtures, as used here, are materials added during the initial mixing of the mortar. They include various compounds that modify one or more properties of the mortar in the plastic and hardened state.

In cold weather masonry construction the admixtures most often encountered are: anti-freezes, accelerators, coloring agents, corrosion inhibitors, and air-entraining agents.

1.2.1. Antifreeze. Most of the commercially available "antifreeze" mixtures for mortar are misidentified. They are accelerators rather than mortar freezing point depressants. Some actual antifreeze admixtures are available, which include several types of alcohol. If used in quantities that will significantly lower the freezing point of the mortar, the compressive and bond strengths of the masonry may decrease rapidly. Since antifreeze compounds have little benefit, they are not recommended.

1.2.2. Accelerators. The primary purpose of an accelerator is to hasten the hydration of the portland cement in the mortar. The compounds commonly used as accelerators are: calcium chloride, soluble carbonates, silicates and fluosilicates, aluminous cements, calcium aluinmate, and some organic compounds such as triethanolamine.

(a) Calcium chloride (Ca Cl₂) is the most commonly used accelerator, It is also the main ingredient in the most proprietary cold weather admixtures. Calcium chloride should not be classified as an antifreeze, because the amount required to significantly lower the freezing point of mortar would be so large as to have deleterious effects on mortar properties.

Calcium chloride is an effective accelerator, but 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 spalling of the masonry.

Calcium chloride should not be permitted in masonry containing metal (ties, anchors, and reinforcement). If calcium chloride is 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.

(b) Corrosion lnhibitors. Because accelerators are associated with corrosion failures of metal embedded in masonry, many commercial accelerators now contain corrosion inhibitors. These are usually found in proprietary compounds. Their effect on masonry and cold weather masonry construction has not been evaluated. For these reasons the use of accelerators containing corrosion inhibitors cannot be recommended.

Portable space heater

1.2.3 Coloring agents. The possible effect of coloring agents on cold weather performance of both fresh mortar and the masonry should be considered. Mortar colors should be limited to finely ground metallic oxides, and their quantity should be limited to a maximum of 10 % of the cement content, by weight. Carbon black should be limited to 2% of the cement content, by weight. Coloring agents should be introduced to the mix at the time of initial mixing. The colored mortar should conform to the requirements of the "property specification" of ASTM C 270-Mortar for Unit Masonry, as laboratory tested.

Some coloring agents contain dispersing agents to speed the distribution of the color throughout the mortar mixture. These dispersing agents may act as cement retarders and, consequently, affect the early strength gain of the masonry. In cold weather masonry construction this retarding effect may result in slow-setting, slow-strength-developing mortar, and masonry with a tendency toward efflorescence.

1.2.4. Air-entraining admixtures. Air-entraining admixtures are sometimes used in mortar to "increase workability". There are some data that indicates that laboratory air-entrained mortar specimens are less subject to disintegration due to freezing and thawing in the presence of moisture. Excessive air-entrainment in mortar will result in lower compressive and lower bond strength in masonry. Therefore, air-entraining admixtures should not be used in cold weather masonry construction. This recommendation does not disallow the use of air-entraining cementitious materials.

1.2.5. Summary. Admixtures should not be included in masonry mortars unless they are laboratory tested at the temperature extremes presumably requiring their use. Further, their use should produce the desired effect while used in the construction. Specifiers should be cognizant of the side effects such as corrosion, retardation, and freezing characteristics of the admixtured mortar before selecting any admixture for inclusion within masonry mortars.

Temporary enclosure provides protection
during cold weather construction period

1.3. Material storage. All masonry materials, 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 tempera tures 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.

Test prisms are cured in a heated wood box

The NW Masonry Guide Table of Contents

Masonry Institute of Washington
Washington State Conference of Mason Contractors