What is tuff stone?
Tuff is a natural stone formed from volcanic ash and other ejected material that settled after an eruption and gradually consolidated into rock. It is light, porous and relatively soft. That makes it easy to saw and carve, but also vulnerable to weathering. Its colour ranges from grey and yellowish to brown, depending on the quarry.
Origin
A well-known source in Western Europe is the Eifel region in Germany. In the Middle Ages tuff from the Eifel was shipped down the Rhine, including to the Netherlands, which has no volcanic rock of its own. Especially in Romanesque architecture (roughly the 11th and 12th centuries) tuff was an important building stone for churches and church towers along the major rivers, before fired brick was produced on a large scale.
Finely ground tuff is called trass. Mixed with lime, trass produces a hydraulic mortar that also sets under water.
Application
- Facades and towers of Romanesque churches, often combined with other natural stone.
- Backing masonry and wall infill.
- Raw material for trass and trass mortar.
- Restoration of historic buildings where original stones have to be replaced.
Practical tips
- No hard cement mortar: tuff is soft and porous. A mortar that is harder and denser than the stone traps moisture and makes the stone crumble. Use a lime-based mortar that matches the stone when repairing.
- Keep water away: weathering is fastest where water lingers, such as copings, string courses and the base of the wall. Check gutters and wall copings.
- Match the replacement stone: tuff varies in hardness and colour from quarry to quarry. On listed buildings, let a stone specialist choose the replacement and consult the heritage authority.
- No pressure washing: the jet damages the soft surface.
Related terms
- Trass
- Pozzolan
- Romanesque architecture
- Basalt
- Natural stone maintenance
- Natural stone replacement
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