Why are the insides of tunnels usually covered in ceramic tile?
While not all manmade tunnels are tiled, this type of surface is used for underground roadways and railways all around the world. As it turns out, there are some very good reasons for this. The main reason why tunnels are tiled is the same reason why most showers are tiled. Smooth ceramic tile is fairly easy to clean because particles of dirt and grime generally don’t get imbedded in the material. Instead, most particles collect on top of the tile, and will wash away with detergent and water. This resistance to grime (as well as to moisture) makes tile an extremely durable and easily cleaned material. Even under harsh conditions, it takes a long time for tile to deteriorate, and it’s pretty easy to get all of the grime off. This is especially important in roadway tunnels because of all the exhaust emitted by the cars passing through. These fumes, along with any dirt or roadway salt kicked up by the cars’ tires, gets trapped inside the tunnel, leading to a constant accumulation of gunk
