SAND-LIME BRICKS

Wanganui Chronicle, Volume LXXXIII, Issue 20110, 31 March 1928, Page 14 (Supplement)

SAND-LIME BRICKS

NEW BRITISH PLANTS A comparatively little-known but very efficient method of making bricks, tiles, flags, and building block of all sizes is the sand-lime or silicate-soda process, which is claimed to be superior in many ways to the ordinary burnt-clay-brick method. During recent years the process has advanced by leaps and bounds in many countries overseas, and decided progress is now being made in Great Britain, over a dozen different plants being at work, with an average capacity of 18,000 to 20,000 bricks per eight-hour shift. Ihc process consists essentially of mixing sand with 5 to 10 per cent of its weight of good quality lime, which has been thoroughly slaked, so that no trace of quicklime remains, together with a small amount of cold water. The plastic mass is passed through a continuous brick press, and subsequently the shapes arc heated in a long iron cylinder or autoclave for from four to eight hours by blowing in steam at 1201 b to 1801 b pressure. This effects chemical action between the lime and sand to form hydrated calcium silicates, and thus binds the mass together into an intensely hard, compact, and smooth brick resembling natural stone, the exact duration of the steam-heating depending upon the pressure. The resulting sand-lime brick possesses all tho advantages of the ordinary burnt-clay brick in the way of strength, durability, and porosity, an J theic is no sign of bulging, warping, or twisting, so that every brick is 'a facing .brick. As a result only a thin line of mortar is required, and the bricks are handsome in appearance, with a fine grain and a very light pink or grey colour, according to the sand used.

Plants for the production of those sand-lime bricks have been supplied by a British firm all over the world, and it may be said that the same principle is available for making tiles, paving slabs, and building-blocks, whilst ash clinker, blast-furnace slag, and spent shale may be utilised instead of sand. In these cases steam at atmospheric pressure only is required.