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MORTAR
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MORTAR , the name (1) of a See also:vessel in which any material may be crushed or pounded, and (2) given to various compositions used in See also:building and consisting of See also:lime and See also:cement with See also:sand or other See also:fine aggregate, well mixed by See also:manual labour or machinery with a proper quantity of clean See also:water (see below, and also See also:BRICKWORK). The Latin name both for such a vessel and for the material as mixed in it, is mortarium. The earlier See also:English See also:form morter, from Fr. See also:mortier, has been in See also:modern English more closely adapted to the spelling of the Latin See also:original. As applied to a vessel, the name is chiefly used for one employed in the preparation of drugs, which are pounded or triturated in the " mortar " by means of a pestle (See also:Lat. pistillum; pinsere, to See also:pound). The name has also been given, from a resemblance in shape to the vessel, to a See also:short thick piece of See also:ordnance, resting on a " See also:bed " formerly used for high-See also:angle See also:fire. The See also:barrel was always very short, normally even shorter than it was wide, andsometimes even resembled a bowl in shape. The See also:place of the mortar in See also:artillery is now taken by the See also:howitzer. In modern times the name " mortar " is occasionally used for a particularly short howitzer. (See ORDNANCE.)
Building Mortar.—The sand forming the aggregate is placed on the mixing See also:platform and formed into a See also:ring within which lime in the required proportion is placed; it is then gently but thoroughly sprinkled with clean water through the See also:rose of a watering-can or See also:hose-See also:pipe. The lime is covered with the sand and See also:left undisturbed for a See also:day or two to slake, and the whole See also:mass is then turned over and well mixed with the larry. The mortar is often used immediately the materials are thoroughly incorporated, but it should rather be kept covered over with sacks until well tempered. For large See also:works a mortar See also: See also: In the See also:south of See also:Europe it is the See also:custom to slake lime the See also:season before it is used.
The See also:practical application of mortar to building See also:work, and the methods of pointing the joints of brickwork and stonework, are described and fully illustrated in the See also:article on BRICKWORK.
The results of many careful tests and experiments serve to show that the hardening of mortar is due to several causes acting collectively. With ordinary lime mortars the See also:chief causes of Hardening hardening are the absorption of carbonic See also:acid from the See also:air of mortar. and the See also:combination of part of the water with the lime,
which unites with some of the See also:silica of which the sand is composed and forms silicate of lime. The initial setting is due to the evaporation of the excess of water and to the See also:production of See also:minute crystals of See also:hydrate of lime which slowly absorbs carbonic acid See also:gas from the air. With mortar of See also:rich lime an See also:outer crust is thus formed on the exposed parts which prevents ready See also:access of air to the interior and retards setting. In See also:illustration of this See also:peculiar See also:property of lime to remain soft, some remarkable cases may be mentioned. One of the bastions erected by See also:Vauban in 1666 was removed by See also:General Treissart, in 1822, a See also:hundred and fifty six years after erection. The lime in the interior of the See also:masonry, where it was inaccessible to the action of the atmosphere, was found to be quite soft. Dr See also: See also:Pasley, in removing the old See also:wharf See also:wall at See also:Chatham dockyard in 1834, found that the work executed in lime mortar was easily removable, the mortar being in a See also:state of pulp. The brickwork, built with Roman cement, it was found necessary to blast. The See also:Romans were convinced that it was owing to prolonged and thorough slaking that their works in See also:plaster became so hard and were not defaced by cracks. L. B. See also:Alberti mentions in his writings that he once discovered in an old trough some lime which had been left there five hundred years and that it was quite soft and See also:fit for use. The setting and hardening of hydraulic limes and cements are due mainly to See also:crystallization brought about by the action of water on the silicate of lime, and not by See also:mere absorption of carbonic acid gas from the atmosphere. As a consequence we find that this variety of limes and cements has the valuable property of setting hard while immersed in water and in many cases growing increasingly hard with the See also:lapse of time. Opinions differ very widely on the question of the suitability for building purposes of limes or cements which contain an appreciable proportion of See also:magnesia, many experts holding the view Magnesia in that the expansion which often occurs in floors and other Mortar. works of See also:concrete from one to four years after laying may be justly attributed to the presence of this substance. For mortars, however, it may be assumed that the presence of magnesia is not detrimental to the value of the See also:matrix, but on the contrary may be a source of strength, for experiments show that it reduces the See also:energy of 876 slaking and increases that of the setting processes. Cements containing magnesia are pronounced both by Vicat and Chatoney to resist the dissolving action of See also:sea-water better than those in which no magnesia is See also:present, and it is See also:pretty well established by experience that cements derived from argillo-magnesian limestones furnish a durable cement for construction in the sea. The old mortar of the Romans, which proves its See also:great property of endurance by many of their works still remaining, was in all See also:probability composed of lime mixed with pozzolana or " See also:trass.” These materials are similar in See also:character and are obtained from See also:extinct volcanoes—in the See also:case of the Romans from the See also:Italian volcanoes, but also from extinct volcanoes in the valleys of the See also:Rhine and in See also: This is termed " gauged ' lime mortar. By this addition the strength is greatly increased and the extra cost is but slight.
The following table shows the force required to See also:tear apart See also:common See also:Adhesion stock bricks bedded in mortar, mixed in proportions
commonly used, and left to set and harden for four of Mortar. See also:weeks.
Adhesive Strengths of Lime and Cement Mortars.
See also: . . . I to 6 15i ,, These results show clearly that the adhesive strength of mortar varies according to the proportion of sand used, the power of resistance of the mortar to the force brought to See also:bear upon it decreasing as the proportion of sand is increased. The See also:primary cause of the premature decay which sometimes takes place in mortars and like material is due to the presence of mud and decayed See also:vegetable and See also:animal See also:matter in the sand, or possibly in the lime or cement itself. It is therefore of great importance Decay of to use a perfectly clean sand for the aggregate, and to Mortar. select a lime or cement of good quality for the matrix, care being taken that no See also:foreign matters detrimental to the mortar be introduced during the processes of preparation. The effect of See also:salt in mortars as a preventive of the destructive effects of See also:frost has not as yet been thoroughly determined, and the Effects of few experiments that have been carried out show varying Saitand results. In some See also:German experiments, cubes of stone Frost on were joined together with cement mixed with water of different characters, ranging from pure See also:rain-water to `NOS water containing from 2 to 8% of salt. Before the cement was set the blocks were exposed in air at a temperature varying from 200 F. to freezing-point, after which they were kept for seven days in a warm See also:room. The samples were then examined with these results: The cement mixed with pure water was quite crumbled, having lost all its tenacity. The cement made with water containing 2 % of salt was in rather better See also:condition, while that containing 8% of salt had not suffered from its ex- posure to frost. The use of salt causes much efflorescence on the See also:face of the work, and should therefore not be used where this would be undesirable. Nor should salt be employed for work that is to be subsequently painted. The mortar for the See also:brick facing of the Forth See also:Bridge below water was composed of one part of Portland cement and one part of sand mixed with salt water in a mill. Briquettes made from this See also:compound withstood a tensile stress of an average of 365 lb per square See also:inch when a See also:week old, and of 510 lb at five weeks after mixing. Salt has no effect upon the strength of a mortar, although it retards the setting process somewhat. Cement mixed with a percentage of See also:sugar (usually 2 % and under) has been used with varying success. In See also:India sugar is a frequent ingredient in mortar, probably because it has the effect of preventing too rapid setting; it also retards the drying sugar m of the material. The sugar must be dissolved in the water Mortar• used for gauging, as the results obtained when the sugar is mixed with the other ingredients in a dry state are not good. The addition of sugar to water enables it to take up about fourteen times more lime than pure water. It is supposed by many writers who have studied the methods of the ancients that old Roman mortars contained strong See also:ale, wort or other saccharine matter, and it is probable that the use of sugar with lime passed from India to See also:Egypt and See also:Rome. The following is an See also:extract from the See also:Roorkee See also:Treatise on See also:Engineering, a work of reference published in India: " It is common in this country to mix a small quantity of the coarsest sugar, ' goor ' or ' jagghery, as it is termed, with the water used for mixing up mortar. Experiments were made with bricks joined together by mortar consisting of one part of common See also:shell lime to one and a half parts of sand, one pound of 'jaghery ' being mixed with each gallon of water. The bricks were left for thirteen See also:hours and after that time the average breaking weight of the joints in twenty trials was 61 lb per square inch. In twenty-one specimens joined with the same mortar without the ' jaghery ' the breaking weight was 41 lb per square inch.” Of the saccharine matters used in mortar See also:treacle seems to give the best results, rough See also:cane sugar being next in effectiveness; beetroot sugar is not a good material to use. • The by-See also:laws made by the See also:London See also:County See also:Council in 1891 under sec. 16 of'the See also:Metropolis Management and Buildings See also:Act See also:Amendment Act 1878 require that " the mortar to be used in By-Laws the construction of walls must be composed of freshly affecting the burned lime and clean, See also:sharp sand or grit without earthy See also:composition matter, in the proportions of one of lime to three of sand of mortar. or grit." The cement to be used must be Portland cement or other cement of equal quality to be approved by the See also:district surveyor, mixed with clean, sharp sand or grit in proportions of one of cement to four of sand or grit. Burnt See also:ballast or broken brick may be substituted for sand or grit, provided such material be properly mixed with lime in a mortar mill. The varieties of lime and cement chiefly used for mortar in the See also:British Isles are set forth below: Pure or See also:fat limes should not be used for mortar. Grey stone lime, feebly hydraulic, makes a good mortar, but should not be employed for work below See also:round or in other See also:damp situations. It Limes and is obtained chiefly at See also:Dorking, Hailing, See also:Lewes and Cements for Merstham. It is used in the proportion of one part to mortar. two or three parts of sand. An See also:analysis of the lime from See also:Castle Bytham gives the following composition: 14.00 Silica See also:Iron See also:oxide and alumina 4.25 Lime 77'00 Magnesia 1.25 See also:Carbon dioxide 0.90 Water and loss 2.6o See also:Ioo•do See also:Blue Has lime is eminently hydraulic and should be used in good class work. Its use is a See also:necessity for See also:foundations and work in See also:damn situations where Portland cement is not employed. It is used in the proportions of one part to one or two parts of sand. The best-known varieties are obtained from Watchet in See also:Somersetshire, Barrow-on-Soar in See also:Leicestershire, See also:Rugby in See also:Warwickshire, and Lyme Regis in See also:Dorsetshire. A typical See also:lias lime shows on analysis the following composition: Silica . 17.53 Iron oxide 2.87 Alumina 6.83 Lime 65.84 Magnesia 1.00 Sulphuric anhydride 1.36 Water and carbon dioxide . 3'85 Insoluble matter and loss . 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