How to Plan for Cold Weather Masonry Construction?

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Cold weather masonry construction demands several precautions to be taken by the builders. To avoid seasonal delays associated with cold weather construction, the builder or contractor employs dynamic procedures, equipment, mason contractors, supplies, etc.

As per ACI 530.1-08/ASCE 6-08/TMS 602-08, "Specification for Masonry Structures" provides the minimum requirements for cold weather masonry construction. Masonry construction must be carefully prepared at sites with temperature less than 44^oF or 4.4^oC. Cold weather changes the properties and behavior of the mortar used for masonry, finally leading to cracking and other damaging issues. Hence, masonry construction during cold weather requires special steps to keep the mortar warm and workable.

This article provides insights into the effects of cold weather on mortar and tips to follow for masonry construction during cold weather .

Effect of Cold Weather on Masonry Mortar

Low temperature of the surrounding reduces the temperature of the mortar below normal, which causes the following effects:

1. As the temperature of the mortar falls below normal, the water freezes and causes a volume change, this would result in mortar expansion. Hence, the quantity of water required to reach a given consistency reduces.
2. The hydration process and strength gain of the mortar mix is reduced during lower temperatures. 
3. The initial and final setting time of the mortar are significantly delayed.
4. The freezing of water present in the mortar is just enough to lead to cracks in the mortar. The presence of ice on the surface of masonry units restricts the bond between the mortar and brick units.
5. The rate of strength gain of mortar during cold temperature is reduced.

Tips to Work with Masonry and Mortar in Cold Weather

The general tips to follow while performing masonry construction during cold weather include:

1. The selection of masonry materials for cold weather performance must be optimized.

2. Protecting the raw materials from ice and cold weather.

3. Heating the material and mortar during its application.

4. Insulating the structures during curing (Figure-2) .

5. Protecting or enclosing the work areas (Figure-3).

6. Protect the workers at the site (Figure-4).

The workers seem to be less productive during cold weather. The workers working within a protected area were found to work until 12°F to 2°F as per a field observation conducted by the Portland Cement Association (PCA). A better working area for mixer operators can improve their productivity drastically.

Storing and Handling Materials for Masonry Construction in Cold Weather

1. All the materials used for masonry construction must be prevented from rain and snow. For this, the materials can be placed on planks and covered using tarps.
2. Always select mortar ingredients that are delivered in bulk and dry.
3. The fine aggregates delivered may contain frozen lumps. These can be heated and broken into sand.
4. The masonry units must be placed over unfrozen surfaces. The temperature of the surface must not be less than 20°F. It must be free from ice and snow.
5. Always heat the masonry materials before construction. This facilitates cement hydration.
6. The mortar must be placed on heated surfaces like metals so that that freezing can be prevented.
7. Glass masonry units must not be installed during cold periods.

Mixing Mortar for Cold Weather Masonry

1. Mix the mortar in smaller amounts. It would stop the materials from absorbing the water. Hence, frosting is restricted.
2. Mortar is placed by heating and maintaining temperature. Do not let the mortar undergo excessive drying due to external warming.
3. The sand or water used for mortar can be heated and mixed. It would help in maintaining the mortar temperature below 40°F. 
4. If hot water is used, first mix it with cold sand before adding cement. This is done to avoid flash setting of the cement.
5. The rate of hydration can be increased by employing high-early cement. An accelerator or admixture can be used to serve this purpose. Accelerators are used to increase the rates of early-age strength development. Hence, they do not let the mortar freeze for a shorter period to facilitate the gain of early strength. The details regarding the accelerators and admixtures that are used in masonry mortar are given in ASTM C1384.
6. As per ASTM C 270, admixtures cannot be used unless specified in the project details. Another method that can be used to increase the reaction rates of mortar in cold temperature is by using fineness cement like ASTM C 150 Type III.
7. The masonry must be placed on a sound and unfrozen foundation. Never place it on a surface covered with snow or ice-covered surface. The snow reduces the bond between the masonry unit and the foundation. When this snow melts, the masonry can undergo movement.

Protecting New Masonry Structures from Cold Weather

1. Once the masonry construction is over, cover the walls with plastic. Plastic prevents water from entering into the masonry during temperatures less than 32°F.
2. Temperatures between 32°F and 20°F can result in heat loss. This can be prevented by covering the wall with insulation blankets.
3. When the temperature in the area is between 20°F and 0°F, the walls must be maintained at around 40°F. It can be performed by a 1-inch insulation blanket. Both sides of the masonry wall can be used to heat.
4. Windbreakers can be installed if the wind speed in the area is higher than 15 miles per hour.

The main goal of cold weather construction plan is to reduce and eliminate the undesirable effects of cold weather on masonry materials, construction and workforce in a cost-effective manner. The mason contractor must evaluate the effectiveness and practicality of the techniques employed concerning the specific project and weather conditions.

Frequently Asked Questions

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