How long can mortar be used before it should not be applied?

The correct answer is based on the working time for mortar after it has been mixed. Mortar typically stays workable for about 1 to 1.5 hours under normal conditions. After this period, the mortar begins to lose its workability due to hardening and the evaporation of moisture.

Choosing 1.5 hours indicates an understanding of the practical limits within which masonry work should be completed. Using mortar beyond this duration could lead to bonding issues or weaken the overall structure, as older mortar may not adhere properly to new blocks or bricks, thus compromising the integrity of the construction.

In practice, various factors such as temperature, humidity, and the specific type of mortar can affect its setting time, but the guideline of 1.5 hours is a general standard established in construction practices.