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close this bookWater and Sanitation Technologies: A Trainer's Manual (Peace Corps, 1985)
close this folderSessions
View the documentSession 1 - Water and sanitation issues in third world countries
View the documentSession 2 - Introduction to the training program
Open this folder and view contentsSession 3 - Facilitation skills
Open this folder and view contentsSession 4 - Community mobilization
Open this folder and view contentsSession 5 - Math review
Open this folder and view contentsSession 6 - Concrete and reinforcement
Open this folder and view contentsSession 7 - Project documentation
View the documentSession 8 - Field demonstration: Formwork and pouring concrete
Open this folder and view contentsSession 9 - Introduction to environmental sanitation
View the documentSession 10 - Non-formal health education
Open this folder and view contentsSession 11 - Community water supply case study
Open this folder and view contentsSession 12 - Project planning and management
View the documentSession 13 - Community needs and resource assessment
Open this folder and view contentsSession 14 - Communicable diseases and control
Open this folder and view contentsSession 15 - Excreta disposal systems
View the documentSession 16 - Health education presentations
View the documentSession 17 - Basic drawing and blueprint reading
View the documentSession 18 - Field demonstration: block laying
View the documentSession 19 - Project planning: Latrine construction
View the documentSession 20 - Latrine construction
Open this folder and view contentsSession 21 - Women and water
Open this folder and view contentsSession 22 - Hydrology
View the documentSession 23 - Water supply improvements
View the documentSession 24 - Pumps: Installation, operation, maintenance
View the documentSession 25 - Field demonstration: Pump assembly and disassembly
Open this folder and view contentsSession 26 - Field demonstration: Pipework and plumbing
Open this folder and view contentsSession 27 - Principles of hand-dug shallow wells
View the documentSession 28 - Well site inspection and feasibility survey
View the documentSession 29 - Project planning: Well rehabilitation
View the documentSession 30 - Shallow well rehabilitation
Open this folder and view contentsSession 31 - Gravity water systems: Part I
Open this folder and view contentsSession 32 - Survey and measurement
View the documentSession 33 - Field demonstration: Surveying
Open this folder and view contentsSession 34 - Gravity water systems: Part II
Open this folder and view contentsSession 35 - Principles of spring development
View the documentSession 36 - Spring site feasibility survey and flow measurement
View the documentSession 37 - Project planning: Spring development
View the documentSession 38 - Spring development construction
View the documentSession 39 - Ferrocement technology and construction
View the documentSession 40 - Project planning: Ferrocement water tank
View the documentSession 41 - Ferrocement water tank construction
View the documentSession 42 - Constructing projects in a community
Open this folder and view contentsSession 43 - Proposal writing
View the documentSession 44 - Training review and assessment

Session 39 - Ferrocement technology and construction

TOTAL TIME

Two Hours

OBJECTIVES

* Discuss the theories and principles of ferrocement technology as applied to the construction of water tanks


* Describe the building sequence of a ferrocement water tank

RESOURCES

Ferrocement Water Tanks; S. B. Watt, Chapters 1-12


Slide show or sketches of building sequence for ferrocement water tank

PREPARED MATERIALS

Newsprint and felt-tip pens, one bucket of sand, one bucket cement, plastering gloves, fine sieve, trowel, float, hawk, chicken wire, hoop wire


Slide projector and screen

FACILITATORS

One or more trainers

Trainer Introduction

This session introduces the trainees to ferrocement technology and describes the steps involved in building a small water tank (two to five cubic meters). The slides or sketches must be prepared prior to the session and should illustrate the building sequence for the type of construction which will be used during the program. The reading assignment is long, and trainees should be told well in advance of the session. Emphasize the importance of reading the assignment prior to the session.

PROCEDURES

Step 1

5 minutes


Present the objectives and format for the session.

Step 2

10 minutes


Ask the trainees to name some characteristics of ferrocement. Record the comments on newsprint, and discuss each one.

Trainer Note

Some possible replies are listed below:

- Uses cement-rich mortar
- Contains reinforced wire meshing
- Long-lasting and strong
- Corrosion resistant
- Relatively inexpensive
- Simple equipment requirements
- Simple construction method

Step 3

35 minutes


Demonstration on ferrocement mortar, and application.

Trainer Note

Begin by gathering the buckets of sand and cement, the fine sieve, plastering gloves, trowel, float, and hawk on a large table. Sift the sand through the sieve and mix a small portion of ferrocement mortar in a bucket. Next, explain how to apply mortar by hand using plastering gloves, and with tools using a trowel or float and hawk.

Stress the importance of the following points during the demonstration:

- Use fine clean sand and clean water.

- Mix the dry ingredients well before adding water.

- The standard mix is one part cement to two parts sand (by volume).

- If cost factors dictate, a one to two and a half or a one to three mix may be used.

- Increasing the proportion of cement in the mix makes it more workable, but can lead to shrinkage cracks.

- The dryer the mix, the stronger it will be, providing it has enough water to be workable. The mix must have enough workability to allow it to hold together when squeezed and bond to the reinforcing wire. However, it should be dry to the pinch. In order words, when the mix is pinched, water does not separate out. During construction, a process of trial and error usually leads to a satisfactory mix.

- To apply mortar by hand, scoop up a handful and smear it across the wall using the palm and heel of the hand. Smear with strong even pressure over an area taking care not to overwork the mortar by rubbing repeatedly back and forth.

- To apply mortar with tools, a hawk is held close to the wall and a trowel or float used to scoop mortar from the hawk and smear it up the wall. Again, strong even pressure should be used to apply the mortar and care should be taken not to overwork the mortar moving the tool repeatedly back and forth over the area. Overworking tends to bring the water to the surface and cause the mortar to slump off.

- Generally, two coats of mortar are applied to the outside of the tank and two coats to the inside. A light third coat may be applied to the outside to provide a smooth finish and a cement slurry brushed on to the inside to provide a water tight seal.

- A coat of mortar should be allowed to set up before another coat is applied. However, the first layer should still be green, in other words not completely hardened, when the second layer is applied. This will provide a good seal between layers.

Step 4

10 minutes


Lecturette on proper curing procedures

Trainer Note

Point out that proper curing procedures are essential. Fresh plaster coats must be covered as soon as they have set. Wet burlap sacks, straw, leaves, or plastic can be used. Emphasize that exposure to direct sunlight, wind, or water will adversely affect the final strength and durability. If the mortar loses moisture too quickly, shrinkage cracks will appear. A curing schedule must be set up and strictly followed. It should consist of regular wettings of the tank wall and floor for a couple of days. Then, two or three feet of water can be put in the tank until a week or so has passed. Lastly, the tank can be slowly filled over a few days period.

Step 5

20 minutes


Lecturette on the need for reinforcement in ferrocement water tanks.

Trainer Note

Wire mesh reinforces the mortar by distributing the stress load. It helps prevent the concentration of stress loads in areas of weakness. Tanks are subject to two primary forces: shear stress and hoop stress. Therefore, additional reinforcement is necessary.

Shear stress is greatest at the joint where the foundation meets the walls. It is a result of the stress caused by the weight of the water and the walls. In small tanks, shear stress is handled by making foundation reinforcement or mesh continuous with the wall reinforcement. This distributes the pressure evenly.

Hoop stress occurs in the walls of the tank. It is a result of that pressure being distributed throughout the tank by the use of reinforcement at the joint between the foundation and walls. It is handled by wrapping heavy hoop wire, in a continuous strand, around the tank. Because the pressure is greater at the bottom, more strands are needed there. As you move up the tank, the pressure decreases and less wire is necessary. It is a good ides to wrap a few strands of wire at the top however, in order to support a tank lid.

It is important that the trainees understand these concepts. Use the diagrams on pages 29 through 31 of the Watt book to illustrate the points made.

Step 6

35 minutes


Present the building sequence of a ferrocement water tank project.

Trainer Note

Use this time to explain each step in the process. The steps should include: site selection and preparation, foundation, formwork, reinforcement, plastering, finishing, and curing. Answer all questions the trainees may have.

Step 7

5 minutes


Review the objectives and conclude the session.