1. Pure lime which sets on the outside, but drys without setting inside. 2. Poor lime-a mixture with impurities which do not benefit its setting qualities. 3. Grey stone lime-slightly hydraulic. 4. Blue lias lime-eminently hydraulic. The term 'hydraulic' denotes the capacity for setting in the absence of air, and as such limes as more difficult to slake than others they should be ground before use. Great care should always be bestowed upon the choice of cement, and no hesitation should be shown in refusing any but that which is clearly marked upon the bags in which it is sold as 'Best English Portland Cement. A great quantity of inferior material comes from abroad, and is mostly of a natural type, by which is meant that it is taken out of the ground and packed for shipment in its raw state, irrespective of the fact that it contains a vast quantity of impurities which tend to neutralise its efficacy. Portland Cement is a British invention-not yet a hundred years old, and is made mostly in Kent under the auspices of the Associated Portland Cement Manufacturers (1909) Limited. The choice and use therefore of none but that clearly marked as Best English Portland Cement' will insure the correct proportioning and a satisfactory result. In the main, Portland Cement is made from two raw materials-chalk and clay-which are accurately proportioned and mixed together and then burnt until a hard clinker is produced. This is then finely ground and forms the powder which is called Portland Cement. Concrete is usually measured by the yard cube, and for various uses should be proportioned as follows: The materials used for one cubic yard of cement concrete proportioned as above are: As regards the water required, this should be as pure as possible and free from acids or strong alkalis. The bad quality of the water frequently affects the strength of the concrete. The average quantity of water required for making concrete is from 21 to 24 gallons per cubic yard of dry materials. The aggregate should be broken sufficiently small so that no piece is too large to pass through a 2-inch ring. PRICES Excavation in common soils (earth or gravel) in Excavation as above and carting away whole .yard super. 0 3 Levelling and ramming surface of excavation levelling and ramming Excavation to surface, average 12 in. deep and levelling and ramming Hard core 4 in. thick, filled in and rammed level 12 in. 0 5 09 0 4 0 6 Cement concrete paving and floors (6 to 1) 3 in. thick (yard cube) 12/0 to 14 0 9/0 to 11 0 bushel 3 9 CHAPTER XVI BRICKS STONES: BRICKLAYER'S AND MASON'S WORK: ROOF COVERINGS Bricks and Brickwork. It is not necessary to give here an account of the preparation of the brick earth and the various processes it passes through in the production of bricks. It must, however, be clearly understood that bricks are either burnt in a clamp or in a kiln. A clamp is a stack of raw bricks built up with flues to allow fuel to be burnt within the four-sided pyramid. These bricks are called 'stocks,' and are generally used for the internal parts of walls, also in facing work where it is proposed to rough cast. For these purposes they are well adapted as, in addition to their strength, their rough surfaces provide a very useful key for plaster, both internally and externally. Picked stocks-i.e. chosen for equality of colour are sometimes used for facings. A kiln is a specially prepared chamber of brickwork provided with properly formed flues, which hold from 20,000 to 50,000 bricks. The method by which a brick has been made can be determined as follows: Hand Moulded.-Frog (i.e. depression rectangular in shape) on one side. Somewhat lacking in form and finish, and porous. Machine Made.-Without frogs. Good in form and less porous. Marks indicating wire-cutting noticeable. Pressed Bricks.-Smooth faces on some or all sides, clean and sharp angles. Frog on one or both sides. Trade mark visible within the frog. Even less porous than the above. Clamp Burnt.-Colour not uniform. Coke breeze visible either on surface or when the brick is broken across. Kiln Burnt.-Stripes on the sides of the bricks of light and dark colour. Varieties of Bricks.-Gault Bricks.-Composed of Gault clay. White Suffolks and Beart's Patent Bricks.-Varieties of Gault bricks. Suffolk Bricks.-Made expressly for facings and are expensive. Of an inhospitable and cold colour. Red Bricks.-Very hard and strong. Dutch Clinkers.-Small, well burnt, and hard. Used for paving, and usually 6′′ × 3′′ × 1". Adamantine Clinkers.-As above but harder, denser, and heavier. Pale pink in colour, with smooth surfaces. Enamelled Bricks.-White or yellow surface like china and are used in lavatories, dairies, &c. Salted Bricks.-Thin glazed surface produced by throwing salt into the fire during burning. Fire Bricks.-Will stand excessive heat. Yellow in colour and close in texture. Used for ovens, furnaces, and the like. Attributes and Test of Good Bricks.-Shape and size regular and uniform; compact and flawless. On saturation should not absorb more than about 15 per cent. of their own weight of water, and should part with it freely at moderate temperature. Uniformly burnt, and should give a metallic ring when two are knocked together. Should require several blows before breaking, and should stand carting and handling well. The size of a brick (9" x 4" x 3") is reckoned as including the mortar joint which should exactly make up for the discrepancy in size between the brick in the raw and after burning, as a certain amount of shrinkage naturally takes place. Good brickwork should show four courses to the foot vertically. The two most important bonds in brickwork-i.e. the method of arranging the bricks in juxtaposition to each other in the successive courses of a wall, are: 1. English-stronger of the two. (See Fig. 177.) 2. Flemish-more pleasing in appearance. (See Fig. 178.) The English Bond, as will be seen in the diagram, consists of flat or flash jointed strack or weather jointed (correct) alternate courses of 'headers' and 'stretchers '-i.e. bricks laid across the wall, showing their ends on the face of the wall in the alternate courses, and bricks laid along the wall end to end in the intermediate courses. The Flemish Bond consists of alternate headers and stretchers in each course. As will be seen in the diagram, it is necessary, in order to prevent the vertical joints of one course coinciding with those struck or weather jointed (wrong) of the courses immediately above ) Keyed joint. Crack pointed. bastard Tack FIG. 179 and below, to introduce a 'closer' which measures 21 inches across and must occur as the penultimate member of every other course and at each end. The jointing material which is, of course, necessary to bind the bricks or any other kind of walling together may be either: 1. Lime mortar composed of It must be remembered that whereas lime mortar benefits from being made and left for a few days, and then made up again, cement mortar must always be used immediately it is made, as when the cement has once set it is useless to break it down again. Lime mortar should be composed of pure lime which is non-hydraulic, as the difficulty in slaking hydraulic limes renders the action likely to take place after setting, which results in small patches being blown out. Two cubic feet of sand, 1 of lime, and 74 gallons of water will produce about 2 cubic feet of mortar. |