In a recent demonstration of precast concrete houses and backyard “tepee” bomb shelters, the walls, partitions and roof of a three-room house were erected in just 23 minutes. Semi-bombproof, in that its walls would stop all but the heaviest flying fragments, the house was designed for quick construction for defense industry workers. The| walls, floors and roof panels are precast in forms flat on the ground, and are made of an aggregate which is 60 percent pumice. Only half as heavy as ordinary concrete, it is said to be more resilient to shock. The cost of the precast house is about half that of typical frame construction. After pouring, the panels are allowed to dry for two days, then are lifted into place on the building site with a truckcrane. Welders join the corners and partitions. The small shelter demonstrated with the precast house is of three-inch reinforced concrete and is intended to be buried in the backyard. Impervious to damage except by direct hit, such a shelter | for six persons would cost around $60, plus excavation and charcoal filters if gas defense is required.