Exterior finishing materials are used in exterior walls of the buildings. Commonly used exterior wall facings and materials are discussed in the following paragraphs.
Stone Facing
The term 'stone' usually designates blocks or pieces of the basic rock material. It is one of the oldest building materials known to man. Because of its unique characteristics, stone has been regarded as the preformed material in the construction of permanent buildings.
Stone used for building purposes can be classified according to the form in which it is available commercially, such as :
- rubble (field stone),
- cut stone,
- flag stone (flat slabs),
- crushed rock
Stones which are commonly used in buildings include granite, limestone, travertine, marble,serpentine, sandstone and slate.
Stone work may be divided into three general categories - rubble work, ashlar, trim.
Rubble work involves using stones which have not been cut but which may have had one face - the face that is to be exposed - split or chipped. Two types of rubble work are used, random and coursed. In random rubble work, no attempt is made to produce either horizontal or vertical course lines. In coursed rubble work, horizontal course lines are maintained with no vertical course lines incorporated.
The term ashlar means only that the stone face showing on the finished surface has its beds and joints sawed or dressed. Ashlar stone work can have a rough, smooth or polished finish, depending on the treatment of the face. Coursed ashlar has continuous vertical and horizontal joints and random ashlar has neither continuous horizontal nor continuous vertical joints as shown.
Ashlar work requires the use of cut stone and includes broken ashlar, irregular coursed ashlar and regular coursed ashlar' (Figure 7.2). Field stone always has a rough, irregular appearance as the natural surface or broken surface of the stone is exposed.
Stone trimrmng lnvolves the use of stones cut for a specific purpose and includes quoins, jambs, sills, belts, copings, cornices, lintels, steps and arch stom. Quoins are stones laid at the intersection of two walls. ?hey can be emphasised by letting them project beyond the vertical plane of the wall or by asing a contrasting color or type. Usually they are laid so that they appear alternately as long and short stones on each side of the comer as shown.
Sills are the stones which form the bottom of window and door openings, and these are of two types, slip sills and lug sills. ?he ends of the lug sills extend under the jambs and consequently a part of the wall load, while slip sills fit between the jambs. All sills should have a wash-a slope on the upper surface to provide for water runoff. Sills should also be provided with a to prevent water from running back to the wall along the underside of the sill.
Belts are special stone courses which are built into a wall for a particular purposes. One purpose for a belt course is to provide architectural relief to a large wall of one material or to provide a break in the vertical plane of the wall. A belt course also provides a convenient means of hiding a change in wall thickness as shown.
A coping stone is one which is cut to fit on the top of a masonry wall. It prevents the passage of water into the walls, sheds water to either the inside or the outside of the wall, and gives a finished appearance to the wall as shown.
Cornice stones are also specially cut stones which are built-in to project from a masonry wall near the top to provide the appearance of an eave. Sometimes two or more stones of varying widths are used to provide the projection with adequate support.
Lintels are stones which bridge the top of door and window openings.
Stone steps are made to fit over an inclined concrete slab or to cap steps cast in concrete.
Arch stones are cut to form some particular type of arch over a door or window opening. An arch is thus used in place of a lintel. A number of arch types are used, including semicircular, elliptical, segmental, gothic, and flat. In each case, the stones are cut to form the required outline of an arch.
No comments:
Post a Comment