Ten Tips for Placing Masonry in Hot Weather
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| Adding water to and remixing fresh mortar
is called “retempering” and is considered good masonry
practice. |
Hot weather poses a few challenges for masonry construction. As
ambient temperatures rise, and materials and equipment heat up,
moisture evaporates more rapidly, leaving less water available for
cement hydration. This article outlines ten recognized techniques
to overcome the negative effects of hot weather on masonry construction.
For masonry construction, hot weather is defined as “ambient
temperature exceeding 100°F (37.8°C), or 90°F (32.2°C)
when the wind velocity is greater than 8 mph (12.9 km/h).”
(See LT292 under “Related Publications at the end of this
article.) Compounding factors include low relative humidity and
direct sunshine. As the temperature of mortar increases:
- Workability is reduced
- More water is required to maintain a given workability
- A given amount of air-entraining agent yields less entrained
air
- Initial and final set occur earlier, and evaporation rates
are generally faster
- Units absorb more moisture from the mortar
As a result, the mason will find it more difficult to place mortar
and units. In addition to effects on workability, rapid drying can
result in a lack of sufficient water for hydration of cement in
the mortar. Inadequate hydration can affect normal strength development
of mortar, leading to a reduction in strength. Exposed mortar surfaces
are particularly vulnerable. Evaporation removes moisture more rapidly
from the outer surface of a mortar joint.
Selecting a Mortar Mix for Hot Weather
In hot-weather construction, mortar properties such as water retentivity
and workability should be given careful consideration when selecting
ingredients and mortar type. For example, provided Type N and Type
S mortars are both structurally adequate for a given masonry application,
the increased water retentivity and workability generally associated
with a Type N mortar make it a better choice for construction during
hot weather.
Ten techniques that can be used for construction of masonry in
hot weather include:
- Select workable, water-retentive mortar mixes (see above)
- Schedule construction to avoid hot, midday periods
- Minimize exposure of materials and equipment to direct sunlight
- Use cool water to mix mortar
- Maintain sand piles in damp, loose condition
- Flush metal equipment and wooden mortar boards with cool water
before contact with fresh mortar
- Pre-wet clay masonry units if they have high absorption (high
IRA)
- Don’t spread mortar too far ahead of work
- Place upper units on mortar bed as quickly as possible
- Under extreme drying conditions, use windbreaks, fog sprays,
or wall coverings to assure adequate moisture for curing of mortar
Related Publications for additional
information about hot weather masonry:
Hot Weather Masonry
Construction, IS243
Hot and Cold Weather
Masonry Construction (Published by the Masonry Industry
Council), LT232
Building Code
Requirements for Masonry Structures and Specifications for Masonry
Structures and Commentaries (ACI 530-05/ASCE 5-05/TMS 402-05,
ACI 530.1-05/ASCE 6-05/TMS 602-05) (published by the Masonry Standards
Joint Committee), LT292
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