A masonry contractor is building a CMU wall and discovers that the mortar is setting too quickly in hot weather. What is the most appropriate immediate action?
Correct Answer
D) Discard the mortar and mix smaller batches more frequently
In hot weather, mortar sets quickly and loses workability. The best practice is to mix smaller batches more frequently to ensure proper workability and bond strength.
Why This Is the Correct Answer
Discarding mortar that has begun to set and mixing smaller, more frequent batches is the proper solution for hot weather masonry work. This ensures each batch maintains proper workability and plasticity throughout its use. Smaller batches can be used quickly before the accelerated setting time in hot weather compromises the mortar's bonding properties and workability.
Why the Other Options Are Wrong
Option A: Add more water to the existing mortar
While retarding admixtures can be planned for hot weather work, adding them to mortar that has already begun setting is not effective and may cause unpredictable results. Admixtures should be incorporated during initial mixing, not as a corrective measure after the mortar has started to set.
Option B: Continue using the mortar but work faster
Continuing to use mortar that has lost workability results in poor bond between mortar and CMU units, inadequate joint filling, and compromised structural integrity. Working faster cannot overcome the fundamental problem of mortar that has exceeded its usable working time.
Option C: Add a retarding admixture to slow the set time
Adding water to mortar that has already begun to set (retempering) significantly weakens the mortar's strength and durability. This practice violates masonry standards and can result in poor bond strength, increased permeability, and potential structural issues.
Memory Technique
Think 'Hot weather = Small batches, Fresh catches' - catch the mortar while it's still workable by using smaller amounts more frequently
Reference Hint
ACI 530/530.1 Building Code Requirements for Masonry Structures - Chapter on Construction practices and hot weather procedures
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