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Masonry: Cold Weather Masonry

Tips when working with masonry under cold weather.

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Cold Masonry
Photo by Furclik

Masonry work requires special attention when working temperatures are below 40 degrees Fahrenheit. When temperature drops below this point, masons should act promptly and follow special steps to keep masonry warm and workable. Masonry work in cold weather produces a slower hydration in the mortar and when the water freezes produced a destructive change in volume causing the mortar expansion. If the mortar contains more than 6% water, the expansion due to freezing will be great enough to crack the mortar. If the masonry is rewetted, the architect or engineer should specify how the masonry should be wetted and how to test if the procedure worked. Wet or ice-covered unit surfaces prevent development of a good bond between the mortar and unit.

Masonry Work In Cold Weather Materials

When working masonry under cold weather follow these material tips.

  • It is recommended to use a speed hydration by using high-early cement or by using an accelerator. Caution: Type III cements could change mortar color varying the required appearance.
  • Analyze how admixture could affect cold weather construction and reactions.
  • Place materials on planks and cover them with tarps.
  • All masonry materials should be completely covered to prevent wetting by rain or snow.
  • Some masonry materials might need to be heated prior to use, so cement hydration can occur properly.
  • Masonry units with high rates of absorption will accelerate stiffening.
  • Calcium chloride (at a limit of 2% by weight of cement) is commonly used in concrete as an accelerator, but its use in mortar is prohibited by the Specification for Masonry Structures (ACI 530.1-95/ASCE 6-95/TMS 602-95).
  • Place masonry on unfrozen surfaces because ice reduces bond and when it melts the masonry could move.
  • Mortar Temperatures

    Working under cold or freezing temperatures can cause serious problems if not addressed properly. It is important to keep mortar above 40 degrees Fahrenheit. And you should be able to do it following these steps:

  • Temperature above 32 degrees Fahrenheit- Cover walls with plastic to prevent water entering masonry.
  • Temperature between 32 and 20 degrees- Cover walls with ½ inch insulation blanket to prevent or reduce rapid heat loss, or block water entering masonry.
  • Temperature between 20 and 0 degrees- Cover wall with plastic insulation blanket, approximately one inch thick, or maintain a heated area to 40 degrees for two days following installation.
  • It is important to mix mortar in small amount, so it doesn’t cool before it has been used. If temperatures are too low, mortar can be placed on heated surfaces such as metal mortar boards. Be sure to monitor closely mortar temperature to avoid mortar being dried due to excessive heat.

    Masonry Cold Weather Tips

    The following cold-weather procedures shall be implemented when either the ambient temperature or the temperature of masonry falls below 40ºF.

  • Mortar shall be maintained above freezing until used.
  • Sand or water shall be heated to produce mortar above 40 degrees Fahrenheit.
  • Heat sources might be used on both sides of the masonry under construction.
  • Wind breakers shall be installed if wind conditions are in excess of 15 miles per hour.
  • Glass unit masonry shall not be laid during cold periods.
  • Heated enclosures are recommended when the temperature drops below 20°F.
  • Most commercially-available masonry ‘antifreeze’ admixtures are actually accelerators rather than freezing-point depressants. ASTM C1384 provides criteria for evaluating admixtures, including accelerators, for use in masonry mortars.
  • It may be necessary to heat sand to thaw frozen lumps when temperatures fall below freezing.
  • To avoid flash set, heated water should be combined with cold sand in the mixer before adding cement.
  • Do not lay masonry units having either a temperature below 20°F or containing fro­zen moisture, visible ice, or snow on their surface.
  • Masonry units should be kept dry, although very high absorption fired-clay brick may need to be wetted — but not saturated — prior to use.
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