Concrete shells 50 feet or more in diameter can be built at low cost by two persons having only limited construction skills. This method requires no steel reinforcement and is simpler than shotcreting methods.

HOW TO DO IT

A sandwich of materials is assembled, starting with the inflatable form of polyethylene film, which is laid against the earth. On top goes a layer of nonwoven fabric that becomes reinforcement for the shell. Strips of high-loft polyester fabric are placed within the dry cement-perlite core, and a top layer of needle-punched fabric is placed over it. Thickness of the finished shell is at least 1 inch per 25 feet of span.

PLACING DRY PERLITE MIX

A dry cement and perlite mix containing 2 1/2 to 3 bags of portland cement for each 4-cubic-foot bag of perlite is spread into the fabric with screeds or snow shovels.

WETTING DOWN WITH HOSE SPRAY

When the desired shape and height have been obtained by inflation, the entire shell is wetted down using a hose and nozzle.