For your information, we provide information from various sources.
The National Concrete Masonry Association
"Mortar and Grout Performance
Hydration and strength development in mortar and grout
generally occurs at temperatures above 40 F (4.4 degrees Celcius) and only
when sufficient water is available. However, masonry construction may proceed when temperatures are below 40oF (4.4 C)
provided cold weather construction and protection requirements are followed as described by the Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/TMS 602-02. (Reported by the Masonry Standards Joint
Mortars and grouts mixed at low temperatures have longer
setting and hardening times, and lower early strength than those
mixed at normal temperatures. However, mortars and grouts
produced with heated materials exhibit performance characteristics identical to those produced during warm weather."
Maintain mortar temperature above freezing until used in masonry.
Heat grout aggregates and mixing water to produce grout temperatures between 70 and 120 F (21.1
and 48.9 degrees Celcius). Maintain grout temperature above 70oF (21.1oC) at time of grout placement.
The purpose of an accelerating type of admixture is to
hasten the hydration of the portland cement in mortar or grout.
However, admixtures containing chlorides in excess of 0.2%
chloride ions are not permitted to be used in mortar (ref. 3) due to
corrosion of embedded metals and contribution to efflorescence.
While specifically not addressed by the Specification, the use of
chloride admixtures in grout is generally discouraged.
Noncloride accelerators are available but they must be used in
addition to cold weather procedures and not as a replacement for
them. Antifreezes are not recommended for use in mortars and are
prohibited for use in grouts.
For more information on masonry, techniques and accepted practices:
The Specification for Masonry Structures, ACI 530.1-02/ASCE 6-02/TMS 602-02.
(Reported by the Masonry Standards Joint Committee, 2002.).
The Holcim Cement and Concrete Company:
(which manufactures much of the bagged cement used in sites around Ottawa.)
"Masonry work can be done at temperatures below freezing provided the
materials (including cement), and the resulting mortar from mixing the materials and the
work area is above 5 degrees Celcius.
The masonry work area will need to be protected and heated (usually tarped
in) to keep the masonry work above 5 degrees Celcius for a period of 24 hours at least.
If the masonry cement or mortar are below 5C then hydration of the cement
does not occur and the mortar will be weaker and likely fail."