What characteristic is essential when the mortar is ready for tooling?

The characteristic that indicates mortar is ready for tooling is that it should be thumbprint hard. This state means that the mortar has reached a sufficiently firm consistency that pressing a thumb into it leaves an impression without the material being overly soft or too wet. At this stage, the mortar begins to gain strength but is still workable enough to allow for shaping and finishing techniques to be applied.

Tooling mortar at the right time is essential; if done too early when it is too soft, the shape may deform or the joints may not hold their integrity. If the mortar is too dry or hard, tooling may become difficult or may not produce the desired finish. Therefore, achieving the thumbprint hard stage is crucial for effective tooling, ensuring a well-finished appearance and the longevity of the masonry work.