Pis(' [Valls. —In some parts of Europe the cheap Pis6 work is much used for small houses of two and three stories. Fat looms are mixed with water and gravel (sometimes sand or chopped straw), without cement, and this medium-wet compound is forced into moulds similar to those used for concrete walls. Openings for doors and windows are finished with wooden frames held by iron clamps built into the walls, and can be ornamented with mouldings. Stone and brick decorations may be inserted in the walls, wood not being suitable for such a purpose. The outside, when entirely dry, is usually stuccoed; the inside is roughly plastered, but can receive finer finish if desired.
B in di ng Afortar. —The material usually employed in bind ing structures of masonry is aerial mortar, a mixture of lime and sand. In certain cases, to prevent dampness or to secure greater solidity, a binding material known as cement, with or without admixture of sand, is largely used, and is especially adapted to the construction of bridge piers and abutments. There are several kinds of mortar. The cheaper kind, such as above named, is formed with gravel and lime; the common is composed of sand and lime, the better qualities of the last named containing a:certain quantity of cement.
Linze is obtained by heating the natural carbonate of Eine (limestone) to a high heat in kilns, thus driving off the water and carbonic-acid gas, whereby the weight is diminished about fifty per cent. When about to be used, it is formed into a hydrate by immersion in a proper quantity of water (not an excess), whereby a large volume of heat is given out and the mass becomes soft and pulverulent. When further treated with water to form a paste, carbonic acid is absorbed by it from the atmosphere, and the mortar begins to crystallize, and further hardens after its application to brick or stone; and this phenomenon continues for many years, which explains the fact that the older the mortar, if good, the more it approaches the hardness of stone.
Lime can also be made from chalk and marble, but the former, contain ing much more water than limestone, heats irregularly in the kiln and is often imperfectly burned, resulting in not slaking fully when needed for use. Some affirm that this description of lime absorbs more carbonic-acid gas than any other kind, but this has not been fully proved. Aluch care is needed in the selection of crude material if g-ood lime be desired, since poor limestones contain silica, magnesia, and metallic oxides. As these may vitrify during calcination, the lime formed will not slake freely. Poor limes may, however, be much improved by grinding them just before slak ing, and in such case they may even exceed in durability richer ungronnd limes, especially where water is likely to be near or often to attack the foundations of walls built therewith, or foundations supporting walls built with mortar foinned from such ground lime. Magnesian limestone, when used for producing lime, yields a product that has the disagreeable quality of causing an unsightly efflorescence on wails, especially of brick, in the erection of which it may be employed.
Lime used for mortar should be slaked only when about to be mixed with sand and water, and the proportions for good mortar should be one of lime and three of sand; with use of the best sharp sand and the best lime, four parts of sand may be employed, but this is about the limit. A small quantity of sulphate of lime in the form of plaster of Paris added to mortar will cause it to set much more rapidly and to yield greater strength than ordinary mortar, while allowing the use of a much larger proportion of sand. This kind, where more of the sulplmte is added, is even used as a substitute for hydraulic cements in forming concrete, etc.
Sharp river-sand is the kind usually mixed with lime to form mortar, the best of the latter having- an admixture of ground quartz or fiint, which greatly improves the adhesive quality. Some maintain that very sharp sand or crushed quartz with an inferior lime forms a mortar much superior to that from soft sand, even though the best lime be -used with the latter. Burned clay will form a fair lime, but such is not to be recommended for the better class of work, especially that subjected to dampness. It may be improved by mixture with hydraulic lime, ground ashes, and sharp sand. Slag from iron furnaces, when properly ground, may be used instead of sand, and with good lime produces an excellent mortar. Ground coal ashes, if used at all, should be used sparingly.
Hydraulic Morfar or cement is that formed entirely of certain kinds of arg-illaceous limestones finely pulverized, which when mixed with water alone form the strongest kind of bond; and the better descriptions will, as above stated, harden under water. There aye various rocks containing nearly seventy-five per cent. of carbonate of lime which, when burned and afterward ground, can be used with water as hydraulic mortars without mixture of sand. These form what may be called the medium cements, not hardening under water, but obtaining quickly great firmness and dura bility in the atmosphere. Portland cement, already mentioned, and others resembling it, such as imitations made largely in the United States, form the best hydraulic mortars. Cements are mixed with sand, in the propor tion of from one tc) three of sand to one of cement, along with just enough water; but mixture should be made of them only as they are required for use. The addition of sand in small proportion appears to have a favorable influence on the binding quality and ultimate hardness of the cements. In larger proportions, it has a weakening effect. The better descriptions are frequently used in a fluid condition, called "grout," to flow in among and bind the parts of certain kinds of masonry; in such case but little sand should be -used.