Challenges for Masonry Construction in     Hot Weather  

Adding water to and remixing fresh mortar periodically is considered good masonry practice in hot weather

As summer approaches, the onset of hot weather poses several 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. Compounding factors include low relative humidity and direct sunshine.  

Effects of Temperature Increases on Mortar 

• 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

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 lead to a reduction in mortar strength. Exposed mortar surfaces are particularly vulnerable. Evaporation removes moisture more rapidly from the outer surface of a mortar joint.

Good Hot Weather Masonry Practices 

• Select workable, water-retentive mortar mixes 
• 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
• 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