In Cardiff and South Wales we have a number of different stones that have been used over time for building houses. These stones came from a variety of sources:
1. Red Radyr Stone.
2. Bath Stone
3. Pennant Stone
4. ‘Dock’ stone
1. Radyr Stone is a breccia sandstone from Radyr (oddly enough) which is a sedimentary rock. It contains irregular fragments of white, brown and grey rock. It formed in a hot dry climate where occasional torrential rain led to flash floods. These carried rock debris along wadis, which was then dumped as alluvial fans at their mouths. Over time, the fragments were cemented together with sand and calcium carbonate.
2. Bath Stone is a limestone, another sedimentary rock. It contains a lot of shell fragments cemented together with calcium carbonate. The quarries for this stone are around the Cotswolds in SW England.
3. Pennant Stone is a grey sandstone. Most of the quarries were around the Valleys of South Wales.
4. This is a made up term by me to illustrate where the stone came from. Basically as the ports grew the amount of ballast coming back with the coal and iron ships grew as well. The stone used for ballast came from a variety of sources – SW England, France, Ireland etc. This meant that it was a mix of stone types. This helps to explain why you occasionally hit a lump of granite (very hard igneous rock) when drilling into a stone walled terrace house.
Understanding these stones help us to repair them and maintain them properly. The sandstones and bath stone are permeable, but their porosity varies. Limestone in the Bath Stone and Radyr Stone means that these are softer and more porous than the Pennant Stone, however all should be repaired using permeable / breathable materials. We would recommend using Lithomex for stone repairs as this comes with a great reputation. This is available through Ty Mawr Lime in Brecon.
Also remember that when rendering over stone lime based renders and plasters should be used, NOT cement. If painting stone then use a breathable paint not a standard masonry paint. We would recommend earthborn Silicate paint.