Marble slabs are much used under all bath-room fixtures. In setting the marble slab the floor should be cut out and the floor slab set in to such a depth that the top of it comes about a quarter of an inch above the floor. The floor slab should never be set on top of the floor if the latter is of wood. In connecting a water closet to a floor slab, a brass floor flange and rubber gasket should be used, the former being secured to the slab by means of expansion bolts, and set in plaster-of-paris to give it a good bearing. The floor slab itself should properly be set in plaster-of-paris and leveled, where necessary, to give it a level surface. If not given a good level foundation the slab will be liable to rock.
Slate is another material used to considerable extent for floor slabs.