Vermiculite, a mineral that has few uses in its crude state, becomes, when heated and exfoliated, an expanded light aggregate of great value in the production of lightweight fill and insulating concrete. Since the 1920's, the mining and processing of vermiculite has grown to a better than $30 million a year in industry as of 1961. Compared with conventional aggregates, the price of vermiculite aggregates is relatively high; but the use of vermiculite concrete can result in significant savings in weight of steel. It is also more fire resistant and has heat and sound insulting properties considerably superior to those of conventional concrete. Vermiculite's thermal conductivity (K factor), ranges from .6 to .97 BTU per hour per square foot (degrees F. per inch), depending mainly on the mix ratio. The lighter the concrete, the better (lower) the K factor. The most common use of vermiculite lightweight concrete is for light, structural roof decks, and for insulation fill over metal decking and structural concrete. Vermiculite for roof decks can be placed over various kinds of form boards- fiber, fiberglass, acoustical, and asbestos cement- as well as over paper back wire lath. Vermiculite concrete is highly adaptable for concrete roof systems. Almost any architectural requirement can be met by changing the type of form, slab thickness, concrete mix, or support spacing. Drainage slopes can be incorporated into one monolithic surface and the concrete can be placed on steep inclines.