What should be done when mortar starts to stiffen up?

When mortar begins to stiffen, the most effective course of action is to moisten it. Mortar is a mixture of cement, sand, and water, and its workability is essential for achieving a good bond between masonry units. As it starts to stiffen, it indicates that the chemical reactions within the mixture are occurring and moisture is evaporating, which can hinder its performance.

By moistening the mortar with a small amount of water, you can enhance its workability, allowing it to be manipulated easily without compromising its integrity. This practice helps maintain the right consistency for application, ensuring that it adheres properly to the bricks or stones being used.

Throwing out mortar that starts to stiffen is not practical as it would waste materials and time. Simply adding aggregate or sand also doesn't address the root issue of moisture loss and could disrupt the balance of the mix, leading to weaker mortar. Thus, maintaining the right moisture content is imperative in masonry work to ensure proper bonding and overall durability of the structure being built.