Kentish ragstone is a hard, medium grey limestone quarried in the county of Kent in South-East England. It is drawn from the geological formation known as the Hythe Formation of the Lower Greensand Group, laid down in the Cretaceous period. Ragstone generally occurs in bands between 15 cm and 90 cm thick and alternates between well-cemented and sandy glauconitic bands of stone a loose calcareous sandstone material called Hassock. These bands are generally of similar thickness and the difference in colour between them gives the quarry face a somewhat striped appearance. When the stone is freshly extracted from the quarry, it appears to be of a grey green/blue grey colour; but as it weathers, changes to a more honeyed grey. It is renown for its hard-wearing properties, making it well suited to building stone.
Prior to Roman occupation, most vernacular buildings in England had been built using timber frame infilled with wattle and daub, or in areas where timber was not available, loose stone bedded with earth. Good quality building stone was in short supply in the immediate vernacular and so it was inevitable that the only significant source of hard limestone – Kentish ragstone – would be used in the construction of Roman London which began in 47 AD. Ragstone was very much a key component in the construction of The Roman Temple of Mithras.
Londinium’s location was championed because of its strategic river position adjacent to The Thames, where the river was narrow enough to bridge, but deep enough to allow ships to dock in the tidal waters. The nearest available supply of stone to this was quarried near Maidstone (Medstone) in Kent, known as Kentish Ragstone. It was transported by barge down the river Medway and up The Thames to the Wallbrook. The name Walbrook is thought to originate from the fact that the river/brook ran through The London Wall which ran around the city. The remains of a Roman barge were found in 1962 during construction work on the North bank at Blackfriars, it had been damaged and sunk with 25 tons of Kentish Ragstone on board. Using this as a basis for calculation, it is suggested that approximately 1750 loads of Kentish Ragstone would have been required for building the city wall, construction of which commenced in 190 AD.
Although traditionally difficult to ‘dress’ with a regular face, ragstone has been used for blockwork in the construction of walls and buildings of some of London’s finest properties since the 11th Century; including The Tower of London, The Medieval Guildhall and Westminster Abbey. The building of The Abbey in the 1240’s required such large quantities of ragstone with the result that all local supplies were commandeered for that purpose. A royal command at the time decreed, that “no Kentish ragstone shall be carted to London for any other purpose until the Abbey is built”.
Kentish Ragstone’s use diminished in London during the 17th Century, as brick and Portland stone gained favour and it declined again further in the 19th Century as architectural fashions changed. Although continually used vernacularly in Kent, in recent times, owing to the difficult processes involved and the variable nature of the stone extracted, it has been used as a general construction aggregate, to surface paths or filling for gabions etc.
Recent technological advances however and considerable investment, have now seen bespoke techniques being utilised to liberate the maximum yield of high-quality building stone from the Hassock and has seen Kentish Ragstone being specified more and more in recent projects.
A recent tour of Gallagher’s Quarry near Maidstone (where ragstone from the Hermitage Quarry is still quarried) made these processes clear and provided great insight into both the advantages and limitations of the material. Our visit was in relation to stone being worked for conservation and restoration repairs at Leeds Castle, but other projects for us recently have included; St Andrews Church, Clapham, Aylesford Priory, St Dunstans Church, Frinsted, Knowle House and the aforementioned Temple of Mithras. It is worth bearing in mind however, that of the estimated Million tonnes of stone extracted each year from the quarry, only 1500 tonnes is utilised as fully worked stone. That said, the oldest formal building stone in England does seem to be making a comeback.