The Product Stalite is produced by the rotary kiln method. The rotary kiln is a long, almost horizontal tube which rotates on large bearings and is lined with refractory material. Stalite's kilns are approximately 11 feet in diameter and 160 feet long.
Raw slate is fed into patented preheaters which allow the rock to heat up at a moderate rate.
Here the slate becomes sufficiently plastic to allow the expanding gases to form masses of small unconnected cells. The material is then cooled in a forced air cooling system and conveyed to the classification yard. This cooling process is expensive, but it reduces the chance that the aggregate will crystallize as can happen in water-cooled systems. Stalite's kilns are fired with coal and are not dependent on foreign fuel suppliers. The preheater, burning areas, insulation, and pollution control systems were all developed by Stalite personnel.