Ferrocement

"The last four layers of mesh were stapled to the hull mold. They were laid in the same way as the first layers. The mesh was fastened... as smoothly and as tightly as possible. It was clipped onto the horizontal rods with 3/4-inch (19 mm) hog rings. ...One-half inch (12.7 mm) hog ring staples which do a neater job could not be located ...All edges of the mesh were stapled down tightly so that no stray ends of mesh would penetrate later through the fresh mortar and thus interfere with the plasterers' work... Mesh over the chain link scuppers was clipped away and the ends fastened down neatly."

"The mortar used for the hulls was a mixture of clean, graded silica sand, ...Portland Cement Type II, and drinking-type water. This silica sand, of the grading and particle shape used in high-strength structures... The sand content used was... one 50-pound (22 Kg) bag of coarse grade, one 100-pound (44 Kg) bag of medium grade and one 50-pound (22 Kg) bag of fine grade. To this graded sand was added two 80-pound (31 Kg) bags of Portland Cement Type II and just sufficient water to make the mortar workable into the hull mesh reinforcing. ...There was one plasterer for roughly every 100 square feet (9 m2) ...Retarders or additives were not used. The sun shelters were moved into place ..."

"First a heavy coat was applied all over the hull. Men stationed inside the hull mold began systematically vibrating the mold planking and checking the gaps between the planking for mortar penetration. Once the mortar had all been applied to the satisfaction of the men vibrating and checking, the excess mortar was then scraped back to the mesh. ...A new thin coat was troweled over the hull and allowed to start setting. When it started to set the hull was sponge troweled, the sponge trowel being used in a circular motion to smooth out surface irregularities. As soon as the sponge troweling was finished, the final steel troweling began. This was carried on until the hull surface had set up too hard to be worked on any further, and was as smooth and fair as the plasterers could make it."

"The hulls were steam cured for 24 hours at a temperature of 150°F (66° C). A steam pipe, perforated for its entire length, was placed under the inverted hull and a rubberized canvas steam tent drawn completely over. The temperature was carefully brought up to 150°F (66°C) in a period of four hours. Twenty-four hours were then maintained at this prescribed temperature until, finally, it was allowed to drop slowly to ambient temperature of 85° F (30°C)."

"The hull was left untouched for 18 hours after the plaster finishing work had ceased. This allowed the hull to set-up hard enough for the men to drag the steam tent over it. It is not advisable to start steam curing too soon, as the jets of hot water from the steam pipe may wash some of the mortar off the hull while it is still green. Before steam curing began the wooden screeds were removed from around the hull sheer."

"[These] low cost, easily built, high quality ferrocement roofings... offer an innovative solution to the serious dwelling problem affecting large numbers of people, especially in the marginal urban areas and rural zones of developing countries..."

"Ferrocement was chosen as the material for the proposed roofing because of its physical properties (strength in compression and tension, impact, permeability, etc.) and because it is cheap and easy to build."

"[I]t was decided to develop a type of roofing based on prefabricated sections. ...With the partial results obtained in this stage, another part of the study could be initiated, i.e. to build this same type of element "in situ"... thus providing solutions for situations in which prefabrication is not appropriate..."

"The adaption of ferrocement precast roofings in self-help construction projects... permits the use of standard components which are easily erected without sophisticated equipment."

"The construction of the mold simply consists of making a dome of well compacted earth, covered by a layer of well-finished concrete having a thickness of 8 cm [3.15 inches], with the shape defined by the trusses... used to [shape] the mold."

"The reinforcement consists of two no. 2 bars along the edges, one of them straight and the other one with the necessary bends to provide the handles to lift and fix the dome to the structure. ...[T]wo layers of galvanized chicken wire, guage 22 with a separation of 13 mm are attached to the bars and directly mounted over the mold, one perpendicular to the other. ...[E]nsure a minimum overlap of 5 cm... and... ensure that these are stretched... to achieve the thinnest section possible."

"The mortar used for the mix is made (using a mixture) of normal or ic cement and sand in a proportion of 1:1.5 by volume and with a water-cement ratio of 0.55."