Concrete in freeze/thaw environments is air-entrained. Shouldn't mortars be air-entrained to get better freeze/thaw resistance?
Air-entrained mortar or concrete contains many very small, regularly shaped bubbles in the mixes. In theory, these bubbles resist freeze/thaw damage by providing a space for freezing water to expand into. The bubbles are generated by admixtures during mixing. Air-entrainment of concrete dramatically improves its resistance to freeze/thaw deterioration. Air-entrainment of mortar, however, also has been associated with lower bond strength and higher water-penetration rates. Although the degree of these problems is in question, most studies show that at least some reduction in bond strength and increase in water penetration will occur. The question that should be asked is whether conventional portland cement/lime mortars have adequate resistance to freeze/thaw deterioration without being air-entrained. In walls constructed with proper flashing and good workmanship, freeze/thaw degradation of portland cement/lime mortars has not been a problem. Many walls have lasted well over 50 years in severe exposures such as the Northern and Northeastern United States. I would not recommend air-entrained mortars simply for improved freeze/thaw resistance.