Stone Stairs have an advantage over those of wood, inasmuch as they are much simpler in construction,2 but the steps are heavy and require substantial walls for their support; moreover they become smooth under the friction of continued wear, and then are slippery and dangerous.
Stone Steps are generally solid blocks, and should be worked on the tread and rise, the former being for external steps slightly weathered, or the stone set with a slight inclination outwards.1 In superior buildings the soffit also is worked, and the nosing may be moulded,2 as shown in Fig. 196.
1 Sc. Wheeling steps.
2 Hanging stone steps are soon destroyed by fire; the part exposed to the heat expands, that imbedded in the wall does not, hence the steps snap off at the wail.
Steps and landings that cannot be got out in one stone must be of pieces jointed, joggled, and plugged together; in some cases it is necessary to support the landings on girders. Stone steps are sometimes formed with thin flags forming treads and risers, similar to those of wooden steps. Such steps require no further description. The following remarks refer to solid steps.
Square Steps are rectangular in section, as shown in Fig. 195.
The hatched portion of these figures is in section, the remainder in elevation.
Spandril3 Steps have the lower side cut away so as to form a raking soffit, as.in Fig. 196 ; this is sometimes useful where headway is required under the stairs, it also makes the steps lighter, and is considered to have a better appearance.
Stone steps may in some forms of staircase be supported at both ends by walls; in other cases one end only of each is built into the wall; these latter are called hanging steps.
Steps supported at both ends are of most simple construction. The stone is rectangular in section, of a height exactly equal to the rise, and in width a little more than that of the tread (Fig. 198).
They are about 12 inches longer than the width of the stair, so that a length of 6 inches at each end is built into the adjacent walls.
When, however, these walls do not rise higher than the sides of the stair, the steps are of a length exactly equal to the width of the stair, and the ends are supported by walls built underneath them.
1 Sc. this inclination is called the kilt of the srone. 2 Sc. Bottled or Bottle-nosed. 3 Sometimes called Feather-edged steps.
Hanging Steps are each fixed at one end only; the outer end projects and is without support other than that afforded by the steps below it.
The fixed ends of hanging steps should be let into the wall about 9 inches, and very solidly and firmly built in.
As each step is supposed to depend to a certain extent on the support of the step below it, the joint between the two is so made that the pressure may be transmitted from one step to the other, and the parts in contact may be kept from slipping.
In square steps this is often done by cutting a rebate1 (R R, Fig. 195) along the lower edge of the front of each step, into which fits the upper edge of the back of the step above, or a deeper rebate may be formed along the lower edge of the breast of each step, and the back-joint cut off at right angles to the soffit, as shown at YY in Fig. 197.
If the ends of the steps are securely built into the wall the steps cannot slide, and the rebate is of very little use; in fact, in the very best work it is sometimes omitted, unless the steps have a low rise, and would otherwise be too thin to bear the weight upon them, in which case their thickness can be increased by introducing the rebate.
A plain chamfered joint at right angles to the soffit, like that in Fig. 197 but without the rebate, is sometimes used.
Hanging steps may be built in as the wall is carried up; or, to avoid risk of damage to the steps, indents about 9 inches deep may be left in the walls, and the steps inserted afterwards; they should be pinned in with cement, and iron packing of hoop iron, pieces of old saws, etc.
Sometimes about 12 inches of the walling above and below the steps is built in cement.