Masonry, the art and craft of building or fabricating with stone, clay, brick or concrete block, is one of the oldest of the skilled trades. It dates back to the use of sunbaked clay brick more than 6,000 years ago. Masonry construction helped build some of the world’s most notable structures, including the Egyptian Pyramids, the Roman Colosseum, the Taj Mahal and the Great Wall of China. Read more
As we explained in our last post about cold weather masonry work, the 40°F-mark is important when it comes to working with mortar. It’s important to keep the mortar heated above 40°F, but it’s understood that you can’t always control the air temperature (at least not easily). Here are some important steps to take if you’re doing masonry in winter:
- If the temperature is above 32°F, cover the walls with plastic to prevent water from getting into the masonry.
- If the temperature is between 32°F and 20°F, cover the walls with 1/2-inch insulation blankets to prevent or reduce rapid heat loss and to block water from getting into the masonry.
- If the temperature is between 20°F and 0°F, cover the walls with 1-inch, plastic insulation blankets, or maintain a heated area to 40°F for two days after the installation is complete.
It is important to only mix the mortar as you need it, so that it doesn’t become too cold before you use it. If the temperature of your mortar dropping too low becomes a concern, you can keep it warm by placing it on a heated surface, like a metal mortar board. Make sure that you keep an eye on your mortar if you’re trying to warm it, because excessive heat may dry it out.
The following tips apply for all masonry in winter being done in 40°F temperature or colder, or when the temperature of the masonry itself is below 40°F:
- Always heat sand or water to produce mortar above 40°F.
- You can use heat sources on either or both sides of masonry while it’s under construction.
- Install wind breakers if wind conditions exceed 15 miles per hour.
- Do not lay glass unit masonry in cold weather.
- Try to work inside heated enclosures when the temperature drops below 20°F.
- Beware of commercially-produced “antifreeze” admixtures for masonry work, because they are oftentimes just accelerators and not freezing-point depressants. Be sure that the admixtures that you are using are approved for the work you’re doing.
- If temperatures fall below freezing, and you experience frozen lumps in your work, you may need to heat sand in order to thaw the lumps.
- Always add cold sand to heated water in the mixer before adding cement to avoid flash setting.
- If masonry units are below 20°F, or have frozen moisture, visible ice, or snow on their surfaces, do not lay them.
- Although very high absorption fired-clay brick may need to be wetted prior to use, all masonry units should be kept dry before you’re ready to use them.
It doesn’t look like anybody’s going to be working outside today in New York! However, in the weeks to come, it’s important to be mindful of the extra precautions you need to take while working in winter weather. For masons, it’s especially important to be aware of the temperature around 40°F, because once it drops under 40, there is special cold weather masonry protocol they should follow.
Much like we discussed when we looked at cold weather concrete, the hydration process in the mortar is slower than usual in cold weather masonry work. When the water in the mortar freezes, mortar expansion occurs, which is a destructive change in the mortar’s volume. The expansion in any mortar that is more than 6% water is enough to crack the mortar and damage the job. The architect or engineer should specify how the masonry should be wetted if it needs to be rewetted, and should also specify how the masons should test to confirm that the procedure was successful. Remember that wet or icy unit surfaces make it difficult for a firm bond to be made between the unit and the mortar.
Tips for Cold Weather Masonry Work
- It’s helpful to use a speed hydration method, such as using high-early cement or by using an accelerator. Beware that using type III cements may potentially change the mortar color, which can affect the required appearance for your job.
- Be mindful of how admixture could affect cold weather masonry and reactions.
- All masonry materials need to be protected from the elements, especially from being wet by rain or snow. Protect all materials by placing them on planks and covering them with tarps when they’re not being used.
- Consider which of your masonry materials may need to be heated prior to using them in order for cement hydration to properly occur.
- If you’re trying to accelerate stiffening, use masonry units with high rates of absorption.
- Although calcium chloride is often used as an accelerator in concrete (at a maximum of 2% by weight of the cement), it is strictly forbidden to be used in mortar by the Specification for Masonry Structures (ACI 530.1-95/ASCE 6-95/TMS 602-95).