Great Gatehouse, Hampton Court

Natural Hydraulic Limes


Natural Hydraulic Limes are produced by the calcination of limestones containing fine silica and/or clay minerals at a temperature in excess of 1000°C. They are subsequently hydrated and supplied as a dry powder.  The speed of set and ultimate strength depends on various factors including the degree of hydraulicity of the lime itself.  Three grades are available – NHL2, NHL3.5 and NHL5.


As binder in lime mortars where higher compressive strength, faster set, lower porosity or reduced permeability is required. They are used where lime putty mortars are not suitable or unlikely to prove durable - below ground, canal or tidal walls, weathering details, external renders, or external winter working. Natural Hydraulic Limes should be thoroughly mixed with washed sands at 1:2, 1:2.5, or 1:3 by volume (depending on application) and used immediately.


Mortar colour is determined by the sand or aggregate mixed with the putty.

Shelf Life: 

Up to 6 months if stored in original bags and kept dry. Hydraulic limes deteriorate with age and fresh material should always be used.


St. Astier NHL2, St. Astier NHL3.5, St. Astier NHL5. All ex-stock. 25kg and 30kg bags according to grade.

Health & Safety: 

Alkali pH 13. Protect eyes, open cuts and skin.

See Health and Safety data sheet RJ 5.01A.

Alkali (pH 13).


H318 Causes Serious Eye Damage.

H315 Causes skin irritation.


H335 May cause respiratory irritation.


Experienced operatives familiar with the successful use of lime should be employed. Accurate volumetric site-gauging and thorough mixing is essential. Hydraulic limes set by a combination of the hydration of the hydraulic compounds and the slow carbonation of free lime in the presence of moisture. The control of the drying and curing process by ‘tending’ and protecting is crucial to success and long-term performance. It is important that the correct grade is selected - Seek Technical Advice. Protections are essential. Do not use below a temperature of 5°C or above 25°C. Do not use if there is risk of frost.

User must refer to the St Astier website ( for the relevant User Guidelines, Product Data and Health & Safety Data.