Fresh mortar that has not hydrated might develop ice lenses if the mortar were saturated and if a temperature gradient were maintained through the mortar. Normal precautions, however, ensure that mortar will not be saturated and in most cases no sustained thermal gradient exists during the masonry construction period. If hydration is well advanced, the nature of the mortar has changed in such a way that ice lensing is not considered a primary cause of deterioration even if moisture and temperature conditions are favourable. Where ice lensing has occurred it appears to be a secondary mechanism of destruction that develops after the mortar has been cracked or crumbled by normal frost action or some other mechanism. There is no record of ice lensing in sound, dense mortar.
Frost damage can occur in masonry units.
Those used for exterior masonry will seldom reach a degree of saturation sufficiently high to bring about freezing damage during cold weather construction. If freezing should occur the units will usually possess sufficient strength to resist the expansive forces. Back-up units, however, may have lower strength values and may sometimes be exposed to low temperatures during winter construction. If they should reach a high degree of saturation there is potential danger of frost damage. Moisture Content of Mortar Significant research on cold weather masonry has recently been carried out in Scandinavia.