Belmont House, Lyme Regis

Natural Cement

RJ 1.09

Prompt Natural Cement is a beige-coloured fast-setting and quick-hardening hydraulic binder, produced by the calcination of an argillaceous (clay-rich) limestone at a relatively high temperature (c.1200°C), followed by grinding to a very fine powder. It consists mainly of calcium aluminates, calcium sulphoaluminates and calcium silicates but should not include alite (C3S) which requires a kiln temperature of 1260°C.


Prompt Natural Cement is waterproof and is used where this and the fast-setting properties are an advantage, such as for the maintenance of sea walls in tidal locations. It is being increasingly used for the repair of ‘Roman cement’ renders and mouldings as it is considered to be the closest currently available binder. The rapid setting can be delayed by the addition of ‘Tempo’ citric acid retarder.

Shelf Life: 

Up to 3 months in original un-opened bags kept in DRY storage.


25kg bags normally in stock

Health & Safety: 

See Health and Safety Data Sheet RJ 5.01C.

Alkali (pH 13).


H318 Causes Serious Eye Damage.

H315 Causes skin irritation.


H335 May cause respiratory irritation.

Technical Specification: 

Danger symbol: Xi irritant product

Risk phases:

R36/37/38 Irritating to eyes, respiratory system and skin.

R43 May cause sensitization by skin contact (Cr 6+)

Safety phases:

S2 Keep out of the reach of children.

S24/25 Avoid contact with the skin and eyes.

S26 In case of contact with eyes, rinse immediately with plenty of water and obtain medical advice.

S37 Wear suitable gloves.


Prompt Natural cement is a specialist product. Operatives familiar with the mixing and use of Natural cement and experience of its successful use should be employed. Accurate volumetric site mixing is essential. Prompt Natural cement sets by the hydration of the hydraulic components and not by carbonation. The control of the drying and curing process by ‘tending’ and protecting is crucial to success and long-term performance. Do not use below a temperature of 5°C or above 25°C. Do not use if there is risk of frost.