In Catalonia, a system of construction that has long been and still is frequently used is one that consists in laying slim bricks so that only the largest face is visible (the bricks in each course being laid end to end). This process, using plaster, lime mortar or cement for the joints and forming surfaces one or two layers thick, is employed for floors, partitions or walls and also for vaults, which are warped surfaces in space and are known in Catalan as voltes de maó de pla. To construct these, bricklayers generally use flexible wooden battents, although sometimes they simply make do with two rules and a string, and the results can be seen in lofty staircases and ceilings.