688 



FARMERS' REGISTER. 



[No. 10 



Preparation and Vses of Mortar. 



Rationale. — When the hydrate obtained by 

 slacking quicklime is mixed with water to the con- 

 sistence of paste, a small portion oi" the lime is 

 dissolved ; the dissolved lime attracts carbonic 

 acid from the atmosphere, and is precipitated upon 

 that which retnaiiis undissolved, the water is (bus 

 left free to dissolve a new portion of the lime 

 Avhich is in its turn precipitated, and this successive 

 action will be continued so lono; as mosture is pre- 

 sent, or anv portion of quicklime remains. 'I'he 

 cessation of the action arises more usually from 

 the loss of moisture by evaporation, than from the 

 complete solution of the quicklime. A portion of 

 the latter therelbre remains, which is gradually con- 

 verted into carbonate, and thus thesemi- liquid paste 

 is oradually converted into a white solid possessing 

 but little adhesion. !f silica be mixed with the 

 lime and water, the precipitation of the carbonate 

 takes place upon it in pretiirence, and the adhesion 

 between them is stronger than in the former in- 

 stance. Indeed, it appears as if the chemical affinity 

 which exists between lime and silica influences the 

 adhesion, and that the conversion of the carbonate 

 into silicate of lime begins, and continues to go on 

 for ages. It is only in this way that we can ac- 

 count for the long series of years which elapses be- 

 fore mortar attains its limits ot hardness, and a 

 force of aggregation often superior to that of the 

 limestone whence it is made. The theorj' of the 

 formation of a silicate of lime is also corroborated 

 by the act, that even in the most ancient and har- 

 dest mortars, the quantity of carbonic acid which 

 is present, is alway less than would be required to 

 convert the lime into carbonate. For the same 

 reason that the adhesion of the precipitated car- 

 bonate of lime to silica is greater than to other 

 portions of lime or carbonate, the adhesion of 

 mortar to brick or siliceous stones is greater than 

 to limestone. It is however necessary in all cases 

 that the stone or other material which is to be 

 laid in the mortar be moist, or at least do not ab- 

 sorb moisture. If the material absorb water from 

 the mortar, the solution and precipitation no long- 

 er take place, and no adhesion will ensue between 

 the mortar and the stone. In laying brick, there- 

 fore, it is necessary that it be wet before the mor- 

 tar is applied, otherwise no bond will take place. 



Preparation. — The lime intended for the man- 

 ufacture of mortcar should be either recently burnt, 

 or should have been carefully preserved from the 

 action of air. 



Lime which has been long slaked will make as 

 good mortar as recent quicklime, provided the lat- 

 ter condition have been attended to, but as it is 

 more difficult to judge of the fi'eedom from car- 

 bonic acid in slaked than in quicklime, it is consid- 

 ered preferable to use the latter rather than the 

 former. 



When the lime is prepared from a stone which 

 is free li'om impurities, if slakes readily, and may 

 be converted into mortar as the art of slaking is 

 going forward. For this purpose, a sort of basin 

 is formed on the ground, by means of the sand in- 

 tended to enter into the composition of the mortar. 

 The lime is thrown into the middle of this basin, 

 and water gradually poured over it. The quantity 

 of water must be sufficient not merely to form the 

 solid hydrate, but to convert it into the mechani- 



cal mixture known as the milk of lime. As the 

 quicklime falls to powder, it is gradually incorpo- 

 rated with the sand and water by means of a hoe, 

 which is also of use in breaking down those parts 

 of the lime which longest resist the action of the 

 water. 



If the lime be combined with magnesia, it slakes 

 too slowly to permit this method to be employed. 

 Such lime should be placed in a conical pit, water 

 thrown upon it, and then covered up with the sand 

 intended to be mixed with it. Days, or even 

 weeks may elapse, before the whole mass shall 

 have fallen to powder, but after the disintegration 

 is complete, such lime will make as good a mortar 

 as that prepared from a pure carbonate. It is 

 more usual to slake such lime in the neighborhood 

 of the kiln, and to separate the parts which have 

 not fallen to powder by means of a screen, but 

 this method is objectionable, as the finer and rich- 

 er portions are liable to be charged with carbonic 

 acid before they can be transported to the place 

 where the mortar is to be prepared. A method 

 which is preferable to either, consists in plung- 

 ing the magnesian lime into a vessel of wa- 

 ter, where it is permitted to remain until com- 

 pletely pulverized. The excess of water is then 

 drawn otl', and the lime with the residue of water 

 incorporated with sand. The sand which is to be 

 used in making mortar, ought to be made up of 

 angular fragments of quartz. Such sand is found 

 in the bed of running streams, or in diluvial and 

 alluvial deposites from running water. It is de- 

 signated by masons by the epithet sharp. A mix- 

 ture of argillaceous matter deprives it of this qual- 

 ity, but as this may be separated by agitation with 

 water, the necessary sharpness may often be ac- 

 quired by washing the sand. 



For laying brick or well jointed stone, fine sand 

 is to be preferred ; lor common hewn stone, sand 

 of coarser grain ; and for rubble work, the mortar 

 made with coarse sand should be mixed with 

 small pebbles, or rather with angular fragments of 

 a siliceous stone. 



The best proportion of the materials of mortars, 

 is one part of a pure quicklime to three of fine or 

 four of coarse sand. If the lime be of less purity, 

 the qantity of sand must be lessened in such man- 

 ner as to bear the same proportion to the pure 

 earth contained in the limestone. 



The rapidity with which mortar sets may be 

 much increased by the use of quicklime, ground 

 to powder, instead of being reduced to that form 

 by slaking. This method is the invention of Lo- 

 riot, a French engineer, who supposed he had 

 discovered the secret of the hardness of the an- 

 cient mortars. He directs that three parts of 

 slacked lime be mixed with lour of water, and 

 that sixteen parts of pulverized brick or sand be 

 added. After these materials are thoroughly mix- 

 ed one part of quicklime ground to fine powder is 

 to be added. This mortar has not all the valua- 

 ble properties which were anticipated by its inven- 

 tor. It might however, be used to advantage in 

 building in frosty weather. 



Limestones which contain siliceous or argilla- 

 ceous matter are fit fl)r the preparation of mortar, 

 so long as the lime prepared li'om them retains the 

 property of slaking, but the pro))ortion of sand 

 with which they can be mixed must be still further 

 lessened by the bulk of the other earths contained 

 in the limestone. 



