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Short note: hydraulic lime

Short answer

Hydraulic lime contains 5–30% clay, enabling it to set underwater. Made by burning clayey limestone at 1000–1100°C, forming calcium silicates/aluminates. Classified as feebly, moderately, or eminently hydraulic by clay content; it sets slowly with higher strength than fat lime, used for damp masonry and foundations.

Write a short note on hydraulic lime.

Hydraulic lime is lime that contains clay (silica and alumina), usually 5 to 30%, so that it sets and hardens even under water.

Manufacture

Impure (clayey) limestone is burnt at 1000 to 1100 °C. Silica and alumina combine with lime to form calcium silicates and aluminates, which give the hydraulic properties.

Classification (by clay content)

  • Feebly hydraulic: 5 to 15% clay.
  • Moderately hydraulic: 15 to 25%.
  • Eminently hydraulic: 25 to 30%.

Properties

  • Grey or yellowish colour.
  • Slakes slowly with little heat and small expansion.
  • Sets in damp and underwater conditions, with higher strength than fat lime. The setting time depends on the clay content: about 1 to 2 days for eminently hydraulic lime, up to about 3 weeks for feebly hydraulic lime.
  • Less affected by the atmosphere.

Uses

Mortar for masonry in foundations, damp places and thick walls, plastering of exposed surfaces, lime concrete and lime-surkhi mortar.

✓ Answer checked by Claude Opus 5.5 (high effort)

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