Clay tile walls– Clay tiles are rarely found on historic houses, and the most common position for a leak is the floor/wall joint. The mortar joints between clay tiles are also oftentimes a place for seepage. Like concrete blocks, clay tiles have hollow cores that can swell with water. This can form a reservoir of water that leaks into the basement over time. It should be noted that clay tile is fragile and more easily damaged than other masonry materials, so special care needs to be taken when operating on this type of wall.