Replacement stones for Lede stone in Belgian historical monuments

The Lede stone (Lutetian, Eocene) is an important historic building stone used in the NW of Belgium. In Ghent, it is dominant in the post-Romanesque built cultural heritage. Its use was restricted several times by socio-economic constraints. Since quarrying and production started to cease from the seventeenth century, periodic revivals favoured the use of Lede stone for new buildings and restoration projects. Sulphation is the main threat for the Lede stone as black crusts are the most common degradation phenomena on this arenaceous limestone. Around the turn of the nineteenth century, the Belgian Gobertange stone was the most widely used replacement material. Throughout the twentieth century, the use of replacement material shifted towards French limestones. However, their colour, texture and petrophysical properties differ from the Lede stone, for which a natural yellow-brown patina is very characteristic. In order to solve this mainly aesthetic issue, several new stone types are used as replacement stone in the twenty-first century, while many others have been suggested. It remains, however, difficult to find a replacement stone that matches the visual and petrophysical properties of the Lede stone. One remaining Lede stone quarry pit has increased its activity since 2011, offering the opportunity to use new Lede stone as replacement stone.