Q: I am a structural engineer in an architectural/engineering office. A contractor has asked permission to use automotive antifreeze in mortar during cold weather, claiming it is a common practice. Our response has been to deny permission because ASTM requires "clean" water. Do you have any information on this practice? What are the effects on the masonry or mortar?
- A: Automotive antifreeze should not be permitted in mortar. The quantities of ethylene glycol needed to significantly reduce the freezing point of mortar can deteriorate the calcium compounds in portland cement and hydrated lime. Today, because supplies of ethylene glycol are low, many automotive antifreezes are made with other chemicals that may have even worse effects on mortar. Because little test data exists to show what effects antifreeze admixtures have on mortar or embedded metals, no antifreeze admixtures should be allowed. Instead, cold weather masonry work should be performed according to "Recommended Practices & Guide Specifications for Cold Weather Masonry Construction," published by the International Masonry Industry All-Weather Council, 823 Fifteenth St., NW, Washington, DC 20005. This standard recommends heating mortar ingredients and protecting the masonry from the cold. Admixtures, such as calcium chloride, calcium nitrite, calcium nitrate, or calcium formate, are used sometimes too. These admixtures accelerate setting and strength gain of mortar, thereby shortening the time the masonry must be protected from cold weather. But they don't lower the freezing point of mortar. Calcium chloride, the most commonly used accelerator and the least expensive, may cause corrosion of metals. Thus it shouldn't be used in mortar that is in contact with metal. Although not as detrimental as calcium chloride, calcium nitrate also can promote corrosion of embedded metals. I haven't heard of any problems resulting from the use of calcium nitrite or calcium formate--except their expense. They may cost many times as much as calcium chloride.