Limes — initial setting time of hydraulic lime in building works For a typical hydraulic lime, the approximate initial setting time under standard test conditions is:

Introduction / Context:
Hydraulic lime contains reactive silicates and aluminates that enable it to set under water or in damp conditions. Understanding its initial setting time is important for scheduling placing, compacting, and finishing of lime mortars and renders, especially in conservation or masonry repair projects.

Given Data / Assumptions:

• Lime is classified into fat (non-hydraulic) and hydraulic varieties; hydraulic limes set more quickly.
• Standard laboratory conditions (controlled temperature and humidity) are assumed.
• Initial setting time is the moment the paste begins to lose plasticity and cannot be remixed to the original state.

Concept / Approach:
The presence of belite, aluminate phases, and residual clay-derived compounds in hydraulic lime accelerates early stiffening relative to fat lime. While exact values depend on the hydraulicity class, a broadly accepted ballpark for initial set is around 1 hour (about 60 minutes), which allows practical handling yet avoids prolonged vulnerability to disturbance.

Step-by-Step Solution:
Prepare a paste of hydraulic lime and water to standard consistency.Fill the standard mould and test using a Vicat needle suited for limes or an equivalent penetration method.Record the time at which the needle no longer penetrates to the specified depth, indicating loss of plasticity.Typical observation: initial set ≈ 60 minutes for common hydraulic limes.

Verification / Alternative check:
Cross-verify by small field batches; note workable window for trowelling. Compare with manufacturer’s data for natural hydraulic lime (NHL) of comparable strength class.

Why Other Options Are Wrong:
30 minutes is too short for many standard hydraulic limes.

90–150 minutes reflect either weakly hydraulic or cooler ambient conditions but are not the typical reference value.

Common Pitfalls:
Testing at non-standard temperatures; using impure water; delayed gauging; or contamination with pozzolans can shift the set time significantly.

Final Answer:
60 minutes