I just found this great technique for making ferrocement roofs at Steve’s Flying Concrete site. Steve explains how to make roof panels on the ground so you don’t have to plaster overhead. This eliminates the most difficult and awkward step of making ferrocement roofs. The panels can be hoisted in place by crane or with a crew of strong workers.
“My latest idea is pre-fabricated, arched triangle, roof panels. 12 -18 ft wide–On the ground you build arched triangles in a dish shape. Finish the inside of the dish, flip the dish over, set with a crane and this becomes the ceiling of the dwelling.–No overhead plastering. A row of tiles inside, finishes interior ceiling.
The panels can either be set in a circular pattern to form a “dome” or alternating in a line to roof a rectangular shaped room. Building triangular dishes– start with insulation then structural layer and then polish the inside of the dish. THE HARD PART–Turn the dish over and stack it in vertical pile until the crane comes to set 8 dishes. Crane –reality check– for these dishes on the first floor I’d say 4 hrs at $150/ hr is $600– or $75 X 8 panels. Set the dishes and stick them together in the valleys– form work very simple using plaster lath– mix this pour on site, (pour out of a 5 gal bucket) and vibrate from above. 1/2 yd should go a long way.”
More details at Flying Concrete