Hadlow Tower, Tonbridge

Roman Cement

RJ2.06

Roman Cement is a term used to describe certain hydraulic binders produced by the calcination in a coal or coke fired kiln of limestones containing significant clay minerals (principally iron, silica and alumina). The name was adopted in c.1800 because the typical red or brown colour was thought to resemble mortars of the Roman period.

Roman cement was first produced in 1794 by James Parker from the clay-rich septaria of Harwich but similar products including ‘Medina’ and ‘Sheppey’ cements were subsequently produced from the septaria of the Solent and Thames estuary. These were not supplied as hydrates, but mixed with water and sand on site when much heat was produced. They were fast-setting materials much used for run and cast mouldings and external renders.     

As true Roman Cements are no longer available, modern Roman cements are based on a Natural Hydraulic Lime or Prompt Natural Cement, mixed on site with carefully selected and blended aggregates to match the colour and properties of the original. It is normally necessary to analyse the existing material in order to design an accurate matching mix recipe.

Usage/Purpose: 

For the repair or reinstatement of Roman Cement renders and mouldings.

Colours: 

Mortar colour is determined by the sand or aggregate mixed with the hydraulic lime or natural cement. It is normally necessary to include brick dust and sometimes also earth pigments to match the colour and texture of historic samples. 

Shelf Life: 

Hydraulic limes and natural cement deteriorate with age. Use fresh material.

Availability: 

Hydraulic Lime and Natural Cement normally ex stock. It is important to select the correct grade of hydraulic lime.

Health & Safety: 

Alkali pH13. Protect eyes, open cuts, skin.

See Safety Data Sheet RJ 5.01A.

Alkali (pH 13).

Danger:

H318 Causes Serious Eye Damage.

H315 Causes skin irritation.

Warning:

H335 May cause respiratory irritation.

Observations: 

Experienced operatives with experience of the successful use of hydraulic lime or Natural Cement should be employed. Accurate volumetric site mixing is essential. Hydraulic lime mortars do not behave as modern cementitious materials, and set by a combination of the hydration of the hydraulic compounds and ‘carbonation’. Carbonation in the presence of moisture is a slow process and the control of the drying and curing by ‘tending’ and protecting is crucial to success and long term performance. 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.