Suprisingly not all cave walls are made of rock! Most are but others for reasons given below are lined with concrete blocks or spray applied concrete mix (shotcrete). There are a number of reasons why some cave walls need to be lined.
- The most common reason is that some cave homes have been excavated in a fairly soft mud or sandstone material, which means the walls are easily damaged and very difficult to paint successfully.
- In other caves a mineral known as "salitre" (saltpeter) can be seen "growing" from the cave walls and roofs. This can be difficult to seal and paint and if the problem is extensive enough the best solution is to line the caves.
Block lined caves can have a very regular appearance, sometimes with straight walls and ceilings, (most caves are anything but straight). As such, the rooms can look very much like that found in a conventional house or cottage.
With a spray cement lining, a strong steel mesh is first fixed to the cave wall and so follows, fairly closely, the contours of the wall. With the mesh in place the specially prepared mix is sprayed onto the steel mesh to fill and cover it. When the concrete mix is dry it can be spray painted to give an attractive rustic appearance. This method of lining can only be carried out by specialist companies with appropriate equipment and expertise and is similar to "gunniting" carried out in hard rock mines.
It is all a matter of personal taste as to which finish, natural rock, regular block finish or sprayed concrete you find the most attractive.