Limes and Cements for Mortar.—The varieties of lime and cement chiefly used for mortar in the British Isles are set forth below : Pure or 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 ground or in other damp situations. It is obtained in many places including Dorking, Halling, Lewes and Merstham. It is used in the proportion of one part to two or three parts of sand. An analysis of the lime from Castle Bytham gave the following composition :— Silica .......... • 14.00 Iron oxide and alumina ..... . . 4.25 Lime . . ....... . • 77.00 Magnesia ........ . . . 1•25 Carbon dioxide ..... . . . . o•qo Water and loss ...... . . . 2.6o I00.00 Blue lias lime is eminently hydraulic and should be used in good class work. Its use is a necessity for foundations and work in damp 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 and Keyn sham in Somersetshire, Barrow-on-Soar in Leicestershire, Rugby in Warwickshire, Lyme Regis in Dorsetshire, Aberthan in Glamor ganshire, and other places. A typical lias lime showed on analysis the following composition:— Silica ......... , • • Iron oxide ......... . 2.87
Alumina 6.83 Lime . ......... . 65.84 Magnesia . . t•oo Sulphuric anhydride 2.36 Water and carbon dioxide . . 3.85 Insoluble matter and loss . - 0.72 too•oo Portland cement is the best matrix known, since it is the most powerful and the most durable. It is used for mortar wherever great strength, hard-wearing properties, and resistance to damp are required. It should weigh 90 lb. per cu.ft. and be ground fine enough to pass through a standard sieve having 32,400 meshes to the square inch and leave not more than io% residue; not more than 1% residue should remain on a standard sieve having 7,70o meshes per sq. inch. Test briquettes after setting under water for seven days should stand a tensile stress of 400 lb. on a square inch. It is used in the proportions of one part of cement to from one to five parts of sand.
Portland cement of a similar general character to the English cement is made on the continent of Europe and in America. The first American Portland cement was manufactured in 1874 by Mr. David 0. Saylor.
The chief works of reference on this subiect are G. R. Burnell, Limes, Cements, Mortars; Rivington, Notes on Building Construction, Vol. III. ; F. W. Taylor and S. E. Thompson, A Treatise on Concrete, Plain and Reinforced.