Hydraulic means that a binder hardens through a reaction with water and stays hard even under water. The word comes from the Greek hydor (water). Cement and hydraulic lime are hydraulic binders: they set through hydration, not through drying.
Difference from air-setting
- Hydraulic — hardens through water and stays firm in damp or submerged situations (cement, hydraulic lime)
- Air-setting — hardens by taking up carbon dioxide from the air and needs air to set (air lime)
Pure air lime does not harden under water, whereas hydraulic binders do. This makes them essential for foundations, cellars, hydraulic engineering and all brick and concrete work that comes into contact with moisture.
Applications
- Masonry mortar and render — natural hydraulic lime (NHL) for moisture-loaded or load-bearing situations
- Concrete — cement as the hydraulic binder for all structural concrete
- Restoration — hydraulic lime mortars match old masonry well in strength and vapour openness
The degree of hydraulicity determines how quickly and how hard a mortar sets; more strongly hydraulic binders give a harder, less vapour-open mortar.
Related terms
- Hydration
- Cement
- Lime
- NHL
- Mortar
- Air lime
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.