When does mortar begin to harden and become unusable?

Mortar begins to harden and become unusable primarily due to the initial setting time affected by its composition and the environmental conditions such as temperature and humidity. Generally, mortar can remain workable for up to about 2 hours, depending on these factors. The correct choice emphasizes that mortar starts to lose its plasticity and can become difficult to work with approximately 1.5 hours after mixing. This critical timeframe is essential for masons and builders as it informs them about when to apply or finish the mortar.

After this point, the quality of the bond and the mixture's effectiveness can deteriorate significantly. If mortar is used beyond this working window, issues like reduced adhesion and increased potential for cracking can occur, leading to structural challenges. Understanding this timeframe is important for professionals to ensure durable and effective masonry work.