Page 178 - Masonry and Concrete

Masonry Construction Techniques
177
MASONRY CONSTRUCTION TECHNIQUES

measures should be taken to assure continued hydration, strength
development, and maximum bond. Whenever possible, materials
should be stored in a shaded location, and aggregate stockpiles cov-
ered with plastic sheets to retard moisture evaporation. High-suction
brick can be wetted to reduce initial absorption, and metal accessories
such as reinforcing steel, anchors and ties, mixers, mortar boards, and
wheelbarrows can be kept cool by spraying with water.
Additional mixing water may be needed in mortar and grout, and
additional lime will increase the ability of the mortar to retain water
longer. Increasing the cement content in the mix accelerates early
strength gain and maximizes hydration before evaporative water loss.
Adding ice to the mixing water can also lower the temperature of the
mortar and grout and slow evaporation. Water that is too hot can cause
the cement to flash set. Set-retarding or water-reducing admixtures
1
may also be used. Retempering should be limited to the first 1- 2
hours after mixing. Mortar beds should not be spread more than 4 ft.
ahead of the masonry, and units should be set within one minute of
spreading the mortar. Sun shades and windscreens can modify the
effects of hot, dry weather, but consideration should also be given to
scheduling work during the cooler parts of the day.

5.7.5 Moist Curing

Cement hydration cannot occur if the temperature of the mortar or
grout is below 40°F or if the moisture content of the mix is less than
75%. Both hot and cold weather can produce conditions which cause
hydration to stop before curing is complete. These dry outs occur most
frequently in concrete masonry construction and under winter condi-
tions, but may also occur in brick construction and in hot, dry weather.
Dry outs are naturally reactivated when temperatures rise above freez-
ing and rainwater restores moisture to the wall, but until this occurs,
the masonry is temporarily limited in compressive strength, bond, and
weather resistance.
Moist curing methods similar to those used in concrete construc-
tion can help prevent masonry dry outs. Periodically wetting the fin-
ished masonry for several days with a fine water spray will usually
assure that adequate moisture is available for curing, strength devel-
opment, and good bond. Covering the walls with polyethylene sheets
will also retard evaporation and create a greenhouse effect that aids in

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