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close this book Water purification, distribution and sewage disposal for Peace Corps volunteers
close this folder Section 8: The privy method of excreta disposal design for a village
View the document Overview:
View the document The sanitary survey
View the document The pit privy
View the document Example privy designs
View the document Latrine for village use
View the document Thailand water-seal privy
View the document Lesson plans

Latrine for village use

This low cost water seal latrine slab is a single concrete casting. It requires very little space, is sanitary, odorless, easy to install and maintain, and can be used to produce nightsoil fertilizer

Tools and Materials

Foot plate from - See Fig. and

Steel strap iron 2" wide, 1'7" long

3/8' be its 5" long for air vents

Cuter form - made of wood detailed or Fig.

Inner form - made of wood detailed or Fig.

Clay to make water seal form

Cement, sand, stone aggregate up to 1" maximum


Fig. 71 Latrine for Village Use

Details

In villages where space is a premium and the soil can absorb the flushing water, this latrine may be worth serious consideration. A 30" diameter hole eight feet deep is covered with a slab. Most soils have sufficient stability to support the slab. Very loose or sandy soils may require some type Of lining. Any type of simple superstructure can be fitted over it for privacy. If the nightsoil must be used for fertilizer, this method can if used. After the first six months, a new hole is dug, and the slab moved. The fires pit is covered with two feet of dirt. Six months later the night soil in the first pit has been converted to essentially non-pathogenic fertilizer and may be used with reasonable safety. Do not use any nightsoil fertilizer that has not been composted at least three months. The slab is roved back to the first hole and the second covered with two feet of dirt.

The latrine can be cleaned with only 1/2 gallon of water. When this is done, there is no odor nor any flies and it stays quite clean. Thus it is easy to use. Villagers must be urged to provide for a sufficient supply of water to be brought and stored at the latrine in a large container (en. a 4 gallon kerosene tin). A quart container should also be provided. Instructions should be given in the proper method of flushing the latrine. If this is done improperly a large quantity of water will be wasted. Two quarts of water 2-e sufficient to clear the latrine if the water is thrown with a fair amount of force from the narrow end of the latrine.

Installation is so simple that the untrained villager can do it easily. The round one piece construction facilitates moving the slab by rolling it. It is simple to make once the forms and methods are practiced. The materials cost about S1 for a latrine. One trained villager can make three slabs per day, using three forms. The wooden forms cost about $8 each.

A convex foot-plate form about 38" in diameter is made of wood, metal, or concrete. It must be 1" higher in the center than at the edge. See Fig.

Fig. 72 shows the steel ring and inner form in place on the base. The ring is formed of two inch wide strap iron and fastened with a bolt for easy remove, from the concrete slab. The collapsible wooden inner form is detailed in Figure 73 .

The inner form has three pieces Fig. shows the outline of the two side pieces of the form. These must be cut from wood 2 1/4" thick. The 18 1/8" sides and 3 3/4'' sides stay nearly in contact. A wedge shaped piece of wood shown in Fig. holds corner G of the sides one inch apart. the wedge fits along the 9" side. The spring holds the form closed tight against the separation bars while the wedge is inserted and the inner form placed on the base. The dimensions shown for the inner form should only be used as a guide since some inconsistencies have been observed.


Fig. 72 Inner Form of Latrine (Top View)

Two inches of well mixed concrete (cement 1, sand 2, stone chips 2) is placed in the ring and tamped will to compact it. Next the wooden outer form is set up around the inner liner. See Figs 72 and 73. There should be a clearance of not less than 1/2" between the Inner liner and the wooden outer forms. A cement sand mixture (cement 1, sand 2) of plastic consistency is pieced in this inner space and compacted. A 3/8'' bolt through the outer wood form and into the inner form provides an antisyphon vent and helps to hold the loner form in place. See Figs. and

After 48 hours the casting may be pieced on blocks. The clay siphon and wooden inner form removed, and a finish of cement plaster added to cover any imperfections. When this is set a final coat of pure cement is put on. If and a final coat of pure cement is put on. If there Is any defect in the seal it may easily be repaired by putting a little cement slurry (cement and water in creamy consistency) over the defect and adding at once cement plaster to fill the defect.


Fig. 73 Inner form and steel rim in place on base.


Fig. 74A Latrine bowl mold

* is a wooden wedge, used to hold form tight. to remove form from concrete latrine, one knocks out wedge, then removes separation bars; the bottom of the form then contracts.

If the wood is not hard and smooth, a time outer coating may be hammered on to wooden form.

Width of mold a A & B are 4-1/4 and 51/2 in. respectively. The separation bars at A & B are 2-1/2 & 4 in. long respectively.

Finished bowl-seal form, ready for placing on wooden base. The water-seal form has been molded from clay, by hand, and placed on top of the wooden bowl form. The size and configuration of the water-seal form must be shaped carefully, as shown. This is not difficult.


Fig. 74B Latrine bowl mold


Fig. 74C Latrine bowl mold


Fig. 74D Latrine bowl mold


Fig. 75 Concrete slab has been poured; part of the exterior sectional mold has been placed in its position.


Fig. 76 Rough exterior knock-apart mold made to fit around the clay core with a clearance of 1/2 in. to 3/4 in.

Wooden constituents of above mold:

1. 4" x 4" x 36' - 2 pieces

2. 3" x 4" x 16" - 2 pieces

3. 3" x 4a x 16" - 2 pieces

4. 3" x 3" x 21" - 1 pieces

5. 2" x 5" x 13" - 1 pieces

5. 4" x 4" x l" - 1 pieces

7. 5" x 13" x 1" - 1 piece

8. 3" x 4" x 4" - 1 piece


Fig. 77 Sectional view after pouring the cement in bowl and trap. Note the concave shape of the base plate.


Fig. 78 Transverse section of the casting with forms in place.


Fig. 79 Section of the casting after removal of the forms.


Fig. 80 Completed casting set up on bricks where the wooden inner form is removed and clay siphon lining dug out. The final finish of cement plaster and neat cement polish is applied.


Fig. 81 The completed casting from above showing the dimensions.