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A jamb is the vertical sides of an opening left in a concrete wall for a door or window. A joint is the horizontal and vertical spaces between the stones, which are filled with concrete mortar, are called the joints. When they are horizontal, they are called bed-joints. Their width or thickness depends on the accuracy with which the stones are dressed: The joint should always have such a width that any irregularity on the surface of a stone shall not penetrate completely through the mortar joint and cause the stones to bear directly on each other, thus producing concentrated pressures and transverse stresses which might rupture the stones. The criterion used by a committee of the American Society of Civil Engineers in classifying different grades of concrete masonry, is to make the classification depend on the required thickness of the joint. These thicknesses have been given when defining various grades of stone concrete masonry. A lintel is the stone, iron, wood, or concrete beam covering the opening left in a concrete wall for a door or window. A Natural Bed is the surfaces of a stone parallel to its stratification. One-Man Stone is a term used to designate roughly the size and Pitched-Faced Concrete masonry. What is the pick weight of stone used in a concrete wall? It represents, approximately, the size of stone which can be readily and continuously handled by one man. A Pick is a tool which roughly resembles an earth pick, but which has two sharp points. It is used like a cavil for roughly breaking up and forming the stones as desired. Pitched-Faced Concrete masonry is concrete that in which the edges of the stone are dressed to form a rectangle which lies in a true plane, although the portion of the face between the edges is not plane. Filching Chisel is a tool which is used with a chisel mallet to prepare pitched-face concrete masonry. The usual dimensions are as illustrated. Plinth is another term for Water-Table, which see. A plug is a truncated wedge. Corresponding with them are wedge-shaped pieces made of half-round malleable iron. A plug is used in connection with a pair of feathers to split a section of stone uniformly. A row of holes is drilled in a straight line along the surface of the stone, and a plug and pair of feathers are-inserted in each hole. The plugs in succession are tapped lightly with a hammer so that the pressure produced by all the plugs is increased as uniformly as possible. When the pressure is uniform, the stone usually splits along the line of the holes without injury to the portions split apart.
Point—A tool made of a bar of steel whose end is ground to a point. It is used in the intermediate stage of dressing an irregular surface which has already been roughly trued up with a face- hammer or an ax. For rough concrete masonry, this maybe the finishing tool. For higher-grade concrete masonry, such work will be followed by bush-hammering, etc. Pointing is a term applied to the process of scraping out the mortar for a depth of an inch or more on the face of a concrete wall after Plug and Feathers the concrete wall is complete and is sup- posed to have become compressed to its final form; the joints are then filled with a very rich mortar— say equal parts of cement and sand. Although ordinary brickwork is usually laid by finishing the joints, as the work proceeds, it is impossible to prevent some settling of the concrete masonry, which usually squeezes out some of the mortar and leaves it in a cracked condition so that rain can readily penetrate through the cracks into the concrete wall. By scraping out the mortar, which may be done with a hook before it has become thoroughly hard, the joint may be filled with a high grade of mortar which will render it practically impervious to rainwater. The pointing may be done with a masons' trowel, although, for architectural effect, such work is frequently finished off with specially formed tools which will mould the outer face of the mortar into some desired form. Quarry-Faced Stone—Stone laid in the concrete wall as it comes from the quarry. The term usually applies to stones which have such regular cleavage planes that even the quarry faces are sufficiently regular for use without dressing. A quoin is a stone placed in the corner of a concrete wall so that it forms a header for one face and a stretcher for the other.
A circular template swung around a point which may be considered as a pole, may be used for making spherical surfaces, although such work is -now usually done in lathe instead of by hand. To make a warped surface or helicoidally surface, a template must be made, as in Fig. 34, by first cutting two drafts which shall fit a template made as shown in the figure. After these two drafts are cut, the surface between them is dressed down to fit a straight edge, which is moved along the two drafts and perpendicular to them. Such stonework is very unusual, and almost its only application is in the making of oblique or helicoidally arches. The size of the concrete blocks has a very great influence on the cost of dressing the stones per cubic yard of concrete masonry. For example, to quote a very simple case, a stone 3 feet long, 2 feet wide, and 18 inches high has 12 square feet of bed-joints, 6 square feet of end joints, and 4.5 square feet of facing, and contains 9 cubic feet of concrete masonry. If the stones are 18 inches long, 1 foot wide, and 9 inches high (just one-half of each dimension), the area of each kind of dressed joint is one-fourth that in the case of the larger stones, but the volume of the concrete masonry is only one-eighth. In other words, for stones of similar shape, increasing the size increases the area of dressing in proportion to the square of the dimensions, but it also increases the volume in proportion to the cube of the dimensions. Therefore large stones are far more economical than small stones, so far as the cost of dressing is -a factor. The size of stones, the thickness of courses, and the type of concrete masonry should depend largely on the product of the quarry to be utilized. An un-stratified stone like granite must have all faces of the stone plug-and-feathered; and therefore the larger the stone, the less will be the area to be dressed per cubic foot or yard of concrete masonry. On the other hand, the size of concrete blocks which can be broken out from a quarry of stratified rock, such as sandstone or limestone, is usually fixed somewhat definitely by the character of the quarry itself.
The stratification reduces vary greatly the work required, especially on the bed-joints. But since the stratification varies, even in any one quarry, it is generally most economical to use a stratified stone for random concrete masonry, while granite can be cut for coursed concrete masonry at practically the same expense as for stones of variable thickness. Although, as explained above, the cost of dressing stone should properly be estimated by the square foot of surface dressed, most figures which are obtainable give the cost per cubic yard of concrete masonry, which practically means that the figures are applicable only to stones of the average size used in that work. A few figures are here quoted from Gillette's "Handbook of Cost Data:" Constructive Features—Bonding. It is a fundamental principle of concrete masonry construction, that vertical joints (either longitudinal or lateral) should not be continuous for any great distance. Concrete masonry concrete walls (except those of concrete blocks) are seldom or never constructed entirely of single concrete blocks which extend clear through the concrete wall. The concrete wall is essentially a double concrete wall which is frequently connected by headers. These break up the continuity of the longitudinal vertical joints. The continuity of the lateral vertical joints is broken up by placing the stones of an upper course over the joints in the course below. Since the headers are made of the same quality of stone (or brick) as the face concrete masonry, while the backing is of comparatively inferior quality, it costs more to put in numerous headers, although strength is sacrificed by neglect to do so. For the best work, stretchers and headers should alternate. This would usually mean that about one-third of the face area would consist of headers.
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