Resource Information from the International Masonry Institute Section 2.5.6 (October 2005) COLD WEATHER MASONRY CONSTRUCTION  Successful cold weather masonry construction requires knowledge of code requirements and superior planning capabilities, along with the capacity to be flexible and innovative. The code provides prescriptive targets that must be met within several ranges from 40o F downward, but it also allows considerable latitude to the contractor for their individual methods of reaching the targets. This is in recognition of the wide variety of winter construction site conditions possible, and the fact that technology, available equipment and methods of construction advance rapidly. Code Requirements The primary objectives to be met under the code are: Maintain mortar temperatures between 40o and 120o F at the time of mixing. Protect materials from moisture, (primarily ice and snow) and contamination from soils, or other surface contaminents. Avoid laying frozen units (those with temperatures of 20o F and below) Protect the completed, or partially completed, masonry for an adequate period of time to prevent freezing of mortar and grout. Both the Masonry Standards Joint Committee Code and Specifications (MSJC Code: ACI 530/530.1-ASCE 5/6-TMS 402/602) and the International Building Code (IBC) separate the provisions for construction of masonry from the protection provisions. The construction provision temperature ranges are based on "ambient" temperatures, that is, the temperature at the site at the time of construction. The requirement ranges of temperature for protection must be read as "mean daily" (average forecast for 24 hours) for ungrouted masonry and "anticipated daily minimum" (forcast low temperature for 24, or 48 hours) for grouted masonry. Construction The code allows heating water and /or aggregates for mortar to achieve the desired material temperatures. Care must be taken not to overheat the water or sand above 140o F as sand can scorch causing discoloration of the mortar, and water that's too hot can cause flash setting. Heating water is probably the most effective technique because of its ability to retain heat and impart it to the other ingredients. When dry mortar ingredients are delivered in bulk and mixed from silos, it's a good practice to at least partially enclose the silo and provide some auxiliary heat to the mixing area to keep the dry ingredients as warm as possible. At the temperature range of 40o - 32o F heating either the sand OR the water will result in acceptable mortar temperatures. At the next range, however, 32o - 25o F, heating BOTH sand and water is needed to achieve the desired temperature. Keeping the materials dry and free of ice and snow may require no more than storing them on pallets covered with a heavy tarp. Moving the proper number of units into the heated building enclosure at the end of the day will provide warmed units for work, but requires an accurate prediction of productivity and adequate interior storage space. Pre-warming the masonry units in a separate enclosure may be an attractive option when combined with "just-in-time" delivery to the scaffold. While it may appear more expensive at first glance, the practice may result in time saved from removing ice and snow from units exposed to the weather. Using a torch to remove ice from units can be done, but caution must be used as they can easily be damaged due to thermal shock. Protection Provisions for the protection of completed masonry can be confusing because of the differing time periods involved for grouted versus ungrouted masonry, and whether Type III cement has been used in the grout. Type III cement in grout produces more heat upon hydration and therefore achieves initial set faster. Admixtures used to accelerate mortar setting can also be used, but only with great caution, as some can cause corrosion of imbedded metals. In addition, these may only be used with the permission of the design professional of record. As indicated in Table 1, the basis for protection requirements for ungrouted masonry is the mean daily temperature at the construction site, that is, the average temperature forecast for the upcoming 24-hour period. Grouted masonry protection is based on the anticipated daily minimum temperature forecast for 24 hours, or 48 hours. For example, if the masonry is grouted and Type III cement has been used in the grout, protection is only required for the completed masonry for 24 hours. If another Type of cement has been used, the protection period is 48 hours. Ungrouted masonry only needs the protection of insulating blankets for 24 hours. Planning Section 1.8C of the MSJC Code and Specification indicates that a plan for cold weather masonry construction must be supplied as one of the project submittals if the job site conditions are anticipated to drop below 40o F at any time during the job. With unanticipated delays, even a job that was supposed to be completed in late summer can easily slip into winter. Therefore, planning is crucial to success and the wise contractor will have considered all contingencies and will be prepared. While protection requirements for enclosures and heat may not be required at certain temperatures, contractors, designers and construction managers should consider that enclosures and heated working space provide for better quality masonry, improved conditions for craftworkers and continuous working conditions. Cold weather masonry can affect productivity, budgets, support labor and scheduling. Some planning and construction tips for cold weather masonry: Reduce grout slump, especially with low absorption units or units with integral water repellants. Use anticipated minimum daily temperatures rather than mean daily temperatures to simplify procedures. Use cold weather requirements from one source (2002/2005 MSJC Table) for consistency, but have other information available for reference. For further information on Cold Weather Masonry Construction, contact IMI at 1-800-IMI-0988. The Masonry Industry Committee - Hot and Cold Weather Masonry Construction NCMA TEK 3-1C (2002) BIA Technical Note 1 (1992) MSJC (2002 & 2005) Requirements for Cold Weather Construction Requirements from top to bottom of chart are cumulative.  General Preparation and Construction Requirements: Store units and other materials in dry conditions off the ground. Do not lay frozen units (those with temperatures below 20o F (6.7o C) or those with visible ice or snow. Do not heat water or aggregates above 140o F (60o C). It's not necessary to heat grout materials unless their temperatures are below 32o F (0oC).  TemperatureRanges  Construction Requirements: Ambient Temperatures (Temperatures during construction)  Protection Requirements: (Based on mean daily temperatures for ungrouted masonry and anticipated daily minimums for grouted masonry for period following construction)  40o F to 32o F Do not lay glass units in temperatures below 40oF. Heat sand or water to achieve mortar temperatures of 40oF to 120oF at time of mixing. Maintain glass unit masonry above 40oF for 48 hrs. Protect newly laid masonry with weather-resistant membrane for 24 hours.  32o F to 25o F Heat sand and water to achieve mortar temperatures of 40oF to 120oF at time of mixing. Maintain materials above 32oF until used. Heat grout aggregates and water, keeping grout above 70oF. Protect newly laid masonry with weather-resistant membrane for 24 hours.  25o F to 20o F Add windbreaks or enclosures when wind exceeds 15 mph (24.1 km/h). Heat masonry to 40oF prior to grouting. Cover new masonry completely with insulating blankets, or equal, for 24 hours. Increase to 48 hours for grouted masonry unless Type III cement only is used.  20o F and below Add auxiliary heat to enclosures. Keep enclosed area above 32oF.  Maintain new masonry temperature above 32oF for 24 hours with heated enclosures, lamps, etc. Increase to 48 hours for grouted masonry unless Type III cement only is used. This document is intended for the use of industry professionals who are competent to evaluate the significance and limitations of the information provided herein. This publication should not be used as the sole guide for masonry design and construction, and IMI disclaims any and all legal responsibility for the consequences of applying the information.