Tufa and tuff

[edit] Introduction

'Tuff' and 'tufa' describe two types of stone – both of which have been used throughout history for construction. The terms are often used interchangeably (sometimes erroneously) but they have totally different origins. Despite this, and in both cases, the result is a porous, sponge-like rock that is soft, durable and extremely light for a stone; this characteristic has been exploited in its use for vaults as well as external walls.

[edit] Tufa

Tufa (or tufo) is the term applied to a stone that is formed by calcareous particles laid down over many centuries as a sediment at a hot spring, lake shore or other location. Sometimes called ‘tufaceous limestone’ or ‘calcareous tufa’, the calcareous particles are deposited as a precipitate as the water flows over organic material such as twigs, leaves, mosses and shells. When the water evaporates, the organic material becomes calcified to produce a stone with inherently rich, natural patterns.

Tufa is light and was used chiefly from Saxon times to the 14th century. Its main use was one for which it seems to have been specially ‘made’: vaulting – such as in the rebuilding of the choir of Canterbury Cathedral following the fire of 1174, and also for the vaulting in Bredon Church, Worcestershire.

Tufa can be seen used in association with Kentish ragstone at several churches in Kent; with chalk in the Isle of Wight and with carboniferous limestone in Matlock, Derbyshire. The Norman church at Moccas, Herefordshire, is built mostly of tufa. There are also extensive tufa deposits in Worcestershire and in Dorset (where it has been used with Purbeck limestone). In the Cotswolds, Berkeley Castle is the largest building in England to have been constructed mainly from tufa.

Today, tufa is mainly used for gardens and pond features, alpine rockeries, rock walls and fountains.

[edit] Tuff

Tuff is the volcanic variety of the stone and is relatively soft, hence its use in construction. It is formed from successive layers of ash ejected from the vent of a volcano and later compacted over geological time. Volcanic tuff is extremely durable and was used by the Romans as an external facing for buildings.

[edit] Other varieties

Hypertufa is an artificially made stone comprising various aggregates bound by Portland cement. Used as a substitute for natural tufa, its porosity facilitates plant growth and is thus used for pots and garden ornaments. It was originally invented for use in alpine gardens.

[edit] Related articles on Designing Buildings Wiki

• Types of stone.
• Choosing stone.
• Defects in stonework.
• Finding stone to conserve historic buildings.
• Inspecting stone sample panels.
• Kentish ragstone.
• Masonry.
• Modern Stonemasonry.
• Natural stone cladding.
• Natural stone for Interiors.
• Natural stone.
• Patio stone.
• Portland Stone.
• Sourcing stone to repair Exeter Cathedral.
• Stone dressing.