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Chapter 13: Armature Design

The water reservoir armatures illustrated in this chapter are primarily used to estimate quantities of materials. Although it is true that these armature steel plans have worked in the past and the smallest sizes are very simple to build, there cannot be guarantees that they will work in the present.

These steel layouts are actually about the minimum one can expect to hold wet concrete plaster in place until it begins to cure. Curing shrinkage is so strong it lifts the dome roof upward until support structures are hanging instead of supporting. Everyone makes water reservoirs their own way. These are very strong ferrocement water reservoirs. Most sanitary above ground.

Materials lists derived from these drawings provide a good method for thinking through the plan of construction. Add factors like 5 percent for overlaps and 10 percent for unanticipated thick areas and other wasted plaster. The heights of horizontal bars are rounded nominal numbers.

The reason these schematics are not guaranteed is simple; it is impossible to know the quality of materials utilized by individuals who may build a water tank like this anywhere in the world in conditions ranging from the desert valley to a freezing mountain.

The author and ferrocement.com have no knowledge of the materials, workmanship or site conditions used to accomplish these armature designs. All builders should calculate using the methods in chapter one and the strength data for the actual materials put into the armature, especially for larger sizes. The quality of cement and chemical neutrality of sand and water, as well as the attention given to the concrete as it hardens over time, are all important factors which are discussed in detail elsewhere in this manual. If you have further questions, send them to contact@ferrocement.com.

Vertical reinforcing bar of one centimeter (3/8") is sufficient up to 40 cubic meters (10,500 gal), larger size vertical bars are helpful for maintaining a good shape for larger reservoirs.

Notice the additional layer of welded wire on the lower half of the 100 cubic meter size, this illustrates the increasing strength required as volume increases. A little extra care and patience is required as the size approaches two hundred cubic meters and a three meter wall. The three meter wall should have a girdle of 1.5 cm bar at center of wall height. Four hundred cubic meters requires caution and full attention to and consideration for the large weight of fresh concrete plaster on the roof. This is not difficult but, as related in the house building manual, can become dangerous quite suddenly, without warning.

These sizes have all been built many times with cooperative manual labor, and without a pump. Hand work is more relaxed and creates a larger social occaision. The smallest sizes may easily be mixed in a wheelbarrow or using the ancient Roman method of mixing the sand and cement on the ground, or inside on the floor of the cistern. Add hand mixed water via a formed crater on top of the mixed pile. A power plaster mixer will be helpful for the larger sizes, especially if there is a labor shortage.

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