Frost and Lime Mortar
Q Has anyone else been caught by this winter's frost?
A Analysis of the weather patterns in the North of England over the last two years can be compared with laboratory data for frost resistance. The data show that moderately hydraulic lime mortars moist cured at +15oC developed reasonable frost resistance after 14 days. Those cured at 10oC took 28 days and those cured at 5-10oC took 56 days.
In this region a first frost usually occurs in late October but a dangerous persistent frost by late November. Comparing average temperatures with frost resistance development indicates that mortar placed by 1st October would have some resistance by mid-October; mortar placed by 7th October would take until end-October and mortar placed after mid-October would have little resistance until late November. Of course this varies with precise location and degree of protection.
2009 was kind in that the first frost did not come until 1st December and persistent frost until the end-December. 2010 had a first frost late-November and persistent frost soon after so any mortar placed after early October in this region could have been at risk.