January, 19 lo 



AMERICAN HOMES AND GARDENS 



vn 



Sand-Lime Brick: 



By E. W. Smythe 



HERE seems to be a general impression 

 that sand-lime brick is a new and untried 

 building material; scarcely out of the ex- 

 perimental stage. Although sand-lime 

 brick can not boast of a pedigree traced 

 to the time of the Pharaohs or the Tower 

 of Babel, still it has been in use long 

 enough to establish without doubt its quality as a first-class 

 building material. 



Sand-lime brick were first made in Potsdam, Germany, 

 about 1820. Potsdam, situated in central Germany, is 

 surrounded by a broad sandy plain; there being no clay or 

 stone available for building purposes, sand and lime were 

 made into mortar, molded into bricks and allowed to cure 

 from three to four months in the open air. These bricks 

 withstood all the required tests, and increased in hardness 

 with age. The attention of Dr. Michaelis, of Berlin, in 

 1880 was attracted to this peculiar kind of brick, and after 

 experimentation he discovered, that by subjecting the green 

 brick to steam under pressure the brick after a few hours 

 were rendered as hard as though they had been exposed to 

 the atomsphere for many months. After the discovery 

 made by Mr. Michaelis, the manufacture of sand-lime brick 

 increased rapidly throughout Germany and many large 

 plants for their production were erected. 



In our own country the oldest sand-lime brick of which 

 we have any record are those in the walls of a house in 

 Mobile, Ala., built fifty years ago. As to whether these 

 bricks were made in this country or elsewhere is not known, 

 but at any rate they are in good condition and appear to 

 have been made in a manner similar to those first made in 

 Germany. 



But not until 1901 were sand-lime brick manufactured in 

 any considerable quantity in the United States; during this 

 year two plants were in operation. In 1903 there were 16 

 plants; in 1904, 57, and in 1905, 130. At present there 

 are probably about 200 plants. Among these plants there is 

 a great diversity in the manner of handling and combining 

 their materials. These differences occur from local con- 

 ditions and the way in which they hydrate the lime and the 

 manner of incorporating the lime with the sand. 



In a general way, I shall now describe the process of 

 manufacturing sand-lime brick as carried on by the plant 

 in this city, and then refer briefly to some of the methods 

 used by other manufacturers. 



The sand as it is brought in dump cars from the bank is 

 shoveled into an elevator boot from which it is elevated 

 about 35 feet, and discharged upon a vibrating screen. 

 Here it is run through a ^-inch mesh screen and falls into 

 a conveyor over the numerous coils of a steam drier. The 

 sand must be perfectly dry. There can be no half-way 

 place in regard to the dryness of the sand, for you cannot 

 mix sand and lime intimately unless both are thoroughly 

 dry. The wet sand as it rests upon the pipes dries and 

 runs down into a hopper-shaped bin in the bottom of which 

 is a conveyor for drawing the sand out as it is needed. 



The lime is slacked in water-tight steel boxes mounted 

 on wheels. Each of these has a capacity of about 450 

 pounds of dry slacked lime, a quantity sufficient for one 

 thousand brick. The quicklime is weighed out, placed in the 

 boxes and the proper quantity of water added to it. To 

 determine the correct amount of water to apply to the lime 



in order that a dry slack may be secured, is not always 

 easy, as the lime when received at the factory is nearly 

 always more or less air-slacked, and also there is consider- 

 able variation in the quality of lime even when the lime- 

 stone comes from the same ledge. After applying the water 

 the lime cars are run under the brick cars in the same 

 cylinder in which the bricks are hardened, and the slacking 

 is thus completed, and the surplus of moisture fif not too 

 great) dried out. The dry slacked lime is now dumped 

 from the cars upon a "grizzly" which takes out all the 

 large cores. Passing through the "grizzly," the lime de- 

 scends into a hopper and is conveyed to an elevator which 

 discharges it into a bolting machine where all the small 

 cores are extracted. Leaving the bolting machine the lime 

 falls into a bin directly opposite the bin containing the dn- 

 sand. 



Between the lime and sand bins is a measuring device, 

 and the dry sand and lime are brought to it by convevors 

 placed in the bottoms of their respective bins. The right 

 proportions being measured out, the mixture is allowed to 

 fall into a preliminary mixer where for two or three minutes 

 the sand and lime receive their first mixing. Passing on 

 from this mixer the sand and lime are fed bv a conveyor 

 into a tubemill where they are thoroughly ground and 

 mixed, and each grain of sand is completely coated with 

 minute lime particles. Leaving the tubemill the mix is at 

 once elevated to a pugmill where just sufficient water is 

 added to cause it to cling together when compressed tightlv 

 in the hand. The pugmill discharges the dampened material 

 Into a 4-mold press. The green bricks are loaded upon cars. 

 1,000 to a car, and run into a large steel cylinder ^o feet 

 long by 6 feet in diameter. After filling the cylinder (which 

 holds a day's run) live steam is turned into It. About two 

 hours are required to bring the steam pressure up to 120 

 pounds per square inch, which pressure is maintained for 

 eight hours. After steaming, the brick are ready for 

 market. Twenty-four hours have elapsed since the sand 

 left the bank until It leaves the cylinder a finished brick 

 ready to lay in the wall. In several instances we have af- 

 forded masons the unusual pleasure of laying hot brick on 

 a cold morning. 



In the process of manufacture just described the lime was 

 slacked before incorporation with the sand, but in some pro- 

 cesses the quicklime is ground, then mixed with the sand 

 and passed through a tube or ballmill. After grinding, the 

 proper amount of water is added, and the mixture Is con- 

 veyed to a silo where it is permitted to slack and cure for 

 24 or 48 hours. It is then withdrawn and made into brick. 

 Others grind but a part of their sand and lime, and some 

 do no grinding whatever. There are some factories which 

 use the damp sand directly as It comes from the bank: to 

 this damp sand damp slacked lime Is added. The two are 

 run through a short pugmill, then to the press and made into 

 brick. The process Is beautiful for its simplicity, but the 

 product is not a credit to the sand-lime industry. 



The materials entering into the uKUiufacture of sand-lime 

 brick are as common as those entering into the production 

 of clay brick, but as all clays are not suitable for making 

 good clay brick so all sands are not suitable for making 

 good sand-lime brick. Fhe sand must be clean and contain 

 a high per cent of silica. Of all the impurities in sand, clay. 

 Continued on page xii. 



