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                             Health And Sanitation
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                              Sanitary Latrines
The proper disposal of human waste (called night soil in many parts of the world)
is one of the most pressing public health problems in many rural communities. The
use of sanitary latrines or privies can be very effective in helping to control
disease, which can be spread by water, soil, insects, or dirty hands. While it is
necessary to have a sanitary water and food supply, sufficient medical service,
and adequate diet to stop disease, the sanitary latrine breaks the disease cycle.
Some sicknesses that can be controlled by widespread use of sanitary latrines are
dysentery, cholera, typhoid, and worms. The human suffering and economic loss
caused by these is staggering. It has been said that half of the food eaten by a
person with intestinal parasites is consumed by the very worms that make the
person sick.
Most countries that have actively participated in the 1980-90 U.N. Decade of
Water Supply and Sanitation have developed latrine designs to meet the sanitary
and cultural requirements of their people. Before building latrines the local health
or development agency should be contacted for their advice and help. A latrine
program must reach most or all of the people. This means a carefully planned,
continuing long-range program with participation by government agencies,
community leaders and most of all by the individual families. Proper latrine
designs that fit the cultural pattern are economically possible and can satisfy the
sanitary needs of a successful latrine program. Selected plans and designs for
sanitary latrines are given in the entries that follow.
The recommended kinds of privies are:
o   Pit privies:   a simple hole in the ground, covered with a properly built
floor and a shelter. It has two forms, the dry pit, which does not penetrate the
water table, and the wet pit, which does. The addition of a ventilating pipe
(see "The Ventilated Pit," page 156 helps reduce odors and fly problems.
o   Water privies:  where a watertight tank receives the nightsoil through a
drop pipe or chute. An overflow pipe takes the digested material to an
underground seepage pit or drainage area.
A water-seal slab may be used to cover either of these types of privies to
provide a completely odorless privy.
Other types of simple latrines are not recommended for general use, because they
usually fail to provide enough sanitary protection.
A good privy should fulfill the following conditions:
o   It should not contaminate the surface soil.
o   There should be no contamination of ground water that can enter springs or
o   There should be no contamination of surface water.
o   Nightsoil should not be accessible to flies or animals.
o   There should be no handling of fresh nightsoil; if it is necessary, it should
    be handled as little as possible.
o   There should be no odors or unsightly conditions.
o   The latrine should be simple and inexpensive to build and use.
Other points to consider:
o   Superstructure can be made from any local building material that will give
    privacy and shelter from rain.
o   The privy can be squat or sit-down type.
o   The opening should be covered when not in use.
o   In water scarce areas, a standard pit latrine can be used. When pit is full
    after several years, latrine is moved to a new pit and old one is covered up
    and marked.
o   If space is limited to change the pit, a permanent location can be maintained
    with a double pit, as in the double septic tank (composting latrine) used in
    Vietnam. The urine is collected separately and diluted for use on crops. The
    composted material is used for fertilizer. One side is used until almost full,
    then it composts while the other side is used.
o   If water is readily available, a water-seal bore hole latrine can be used.
    When almost full, the latrine must be moved.
o   If a permanent location is desired, a double bore hole can be used as in
o   In most countries using water seal latrines the pan and trap are now
    available commercially or from a government agency for a nominal fee or for
o   Consider including a methane (biogas) generator when building new latrines.
Charles D. Spangler, VITA Volunteer, Bethesda, Maryland
Wagner, E.G. and Lanoix, J.N. Excreta Disposal for Rural Areas and Small
Communities. Geneva: World Health Organization, 1958.
Privy Location
Outhouses or privies should be close to the home, but they should be lower than
water sources and far enough away from these sources that they will not pollute
the water.
The information given here covers most normal situations, but it is always best to
have a trained sanitary inspector or engineer review your installation or program.
A latrine site should be dry, well-drained, and above flood level.
If the bottom of a privy pit is in dry soil and at least 3 meters (10') above the
highest water table, there is very little danger that it will contaminate water
supplies. This is because the pollution will move downward no more than 3 meters
with only 1 meter (3.3') of side movement. (See section on "Ground Water"). If
the privy pit enters the water table or comes close to it when the water is at its
highest level, pollution will spread to the ground water over a limited area and
may endanger health.
Figure 1 shows the movement of pollution through the soil. It is particularly

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important to understand this movement when choosing a site for a privy or well.
Put the privy downhill from a water source, or as far to one side as possible. On
flat or gently sloping land, water moves toward the well as though it were going
downhill. This is because when water is removed from a well, water from the
surrounding soil flows toward it. Thus pollution from a nearby privy would move
toward the well. If the land is flat or if the well is downhill from the privy, do
not put the privy closer to the well than 10 meters (33'). In sandy soil, a
distance of 7.5 meters (25') is sometimes enough because sand helps to stop
bacterial pollution.
These rules do not apply in regions containing fissured rocks or limestone
formation. Expert advice is necessary in these cases, because pollution can be
carried great distances through solution channels to the drinking water supply.
It is important to keep the latrine close to the house so that it will be used, but
not too close. Putting the privy downhill also encourages use. People are more apt
to keep a privy clean if it is close to the house.
Remember that all privies have to be closed up or moved when filled. This should
be made easy or there will be a tendency to let them become overfull, which
results in very unsanitary conditions and extra work to put the system in proper
working order. A permanent location can have two pits that are used alternately.
One pit is in use while the other composts before being emptied.
Wagner, E.G. and Lanoix, J.N. Excreta Disposal for Rural Areas and Small
Communities. Geneva: World Health Organization, 1958.
Privy Shelters
Several designs for privy shelters that have been found satisfactory in many parts
of the world are shown in Figure 2.

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The shelter should be built to suit the abilities and desires of the local people,
because sanitary precautions are less important for the shelter than for the pit
and slab. For a properly built shelter:
o   Choose a standardized design for economy in building.
o   Build the shelter to last as long as the pit, 8 to 15 years.
o   Build the shelter to fit the floor slab. It should not be so large that people
    will be tempted to use any part of the floor when the area around the hole
    has been soiled by earlier users. The roof should be 2m (6 1/2') high at the
o   Openings at the top of the shelter's walls, for airing the interior, should be
    10cm to 15cm (4" to 6") wide.
o   Some natural light should be let in, but the structure should give enough
    shade over an uncovered seat or holes that flies will not be attracted.
o   The latrine should be kept neat and clean so that people will continue to
    use it. Paint or whitewash the shelter. Cut back nearby vegetation. The roof
    should have a large overhang to protect the walls and the mound from rain
    damage and to keep the privy area from getting muddy.
Here is a list of tools and materials needed to build one type of privy shelter:
                              Tools and Materials
Corrugated sheet metal roofing: 1.2m x 1.2m (4'x 4') or larger
Wooden posts: 5cm x 5cm (2" x 2") and 20m (66') long
Boards: 2cm (3/4") thick, 20cm (8") wide, 40m (132') long
Hand tools
Paint: 2 liters (2 quarts)
Wagner, E.G. and Lanoix, J.N. Excreta Disposal for Rural Area and Small Communities.
Geneva: World Health Organization, 1958.
Pit Privy
The pit privy is the simplest
recommended latrine or privy. It
consists of a hand-dug hole, a
properly mounted slab, and a
shelter (Figure 3). The addition of

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a ventilating pipe will help reduce
odors and flies. Of the many
existing designs for privies, the
sanitary pit privy is the most
widely applicable.
    Tools and Materials
Materials for building the shelter
Hand tools for digging the pit,
making concrete, and building the
The Pit
The pit is round or square, about 1m (3.3') in diameter or 1m (3.3') on each side,
and usually from 1m (3.3') to 3m (10') deep. The pit may have to be lined with
brick, wood, bamboo, or some other material to keep it from caving in, even in
hard soil. The top 50cm (19 1/2") of the hole should be lined with mortar to make
a solid base for the slab and the shelter.
The table in Figure 4 will help you to estimate the depth of hole to make.

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The Ventilated Pit
The ventilated pit privy system was field tested during the late 1970s by the Blair
Research Laboratories working with the Zimbabwe Ministry of Health (Figure 5).

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The idea was to reduce the health hazard caused by flies attracted to the
standard pit privy. Thousands of the units are now in use in Zimbabwe, as well as
in many other areas where water is scarce.
The Blair design depends on the aerodynamic properties of an efficient flue pipe,
150mm in diameter and about 2.5 meters high. The pipe is fitted onto the
concrete latrine slab over a sealed tank or pit. The temperature difference
between the inside and outside of the pipe causes a convection updraft, drawing
the inside gases from the pit and thus causing a downdraft through the toilet
The toilet opening is kept closely
covered between uses. Flies are
then attracted to odors passing out
the pipe rather than to the pit.
Flies that do get into the pit
travel up the pipe towards the
light. There they are trapped by a
screen over the pipe outlet.
It is essential that the pipe be
large enough to enable the system
to "breathe" efficiently and that it
allow sufficient light to enter the
pit to attract flies into the pipe.
Efficiency is increased by painting
the pipe black to increase the air
flow and by facing it toward the
Equator so it receives the most
The Base
The base (see Figures 3, 6, and 7) serves as a solid, waterproof support for the

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a hard, strong material, it helps to keep burrowing rodents and surface water out
of the pit. The pit lining will in most cases serve as a base although it may need
to be strengthened at the ground surface.
The Slab
A concrete water-seal slab is best. It is inexpensive but it means added labor and
construction. A concrete open-hole slab is the next best, while a wooden floor is
adequate. A built-up floor of wood and compacted soil is sometimes used but it is
difficult to keep clean; as it gets soiled, it is likely to spread hookworm.
The concrete should not be weaker than 1 part cement to 6 parts of aggregate
with a minimum of water. It should be reinforced with strips of bamboo about
2.5cm (1") wide whose weaker fibers have been stripped away. Soak the bamboo in
water overnight before use.
Slabs (see Figure 8) are cast upside down in one operation. The footrests are

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shaped by removing part of the wooden form so as to make two separate indentations
in the wood. Sheet metal is placed around the form so that the metal
extends above the wood to the thickness of the slab. Side walls of the hole and
footrests are made with a slight slope so as to come out easily. The form for the
open hole is removed when the concrete first sets. Slabs are removed from the
forms in about 40 hours and should be stored under water for 10 days or more.
Round slabs can be rolled some distance when carrying is difficult. This is
especially handy when the location of the privy has to be moved when the pit
fills up.
The Mound
The mound (see Figure 3) protects the pit and base from surface run-off that

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otherwise might enter and destroy the pit. It should be built up to the level of
the floor and be very well tamped. It should extend 50cm (20") beyond the base
on all sides. The mound may be built much higher than the ground in areas where
protection is needed against floods and high tides. It will normally be built with
earth removed from the pit or the surrounding area. A stone facing will help to
keep it from being washed away by heavy rains. A masonry or brick step can be
built in front of the entrance door to help keep the floor clean.
Wagner, E.G. and Lanoix, J.N. Excreta Disposal for Rural Areas and Small
Communities. Geneva: World Health Organization, 1958.
Water Privy
A water (or aqua) privy uses a watertight tank in which human excreta and urine
partially decompose. A sewer pipe connects the tank's overflow pipe to an
underground drain area or seepage pit.
This is a sanitary and permanent installation when it is properly built, used daily,
and maintained properly. It can be placed near a building. The first cost of a
water privy is high, but it is not expensive in the long run because it will be
used for many years. It needs some water and cannot be used in freezing
climates. And it is not practical in desert or water scarce areas. The water privy
may not be successful in rural areas with no organized sanitation and health
education services.
The Process
The digesting or decomposing tank is usually made of watertight concrete (see
Figures 9, 10, and 11). A drop-pipe, 10cm (4") in diameter, attached to the squatting

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tank. This forms a water seal, which keeps bad odors from rising into the privy
The decomposition process forms a sludge in the tank. The amount of sludge is
only one-fourth the volume of the total waste deposited in the pit, because some
of the solid matter breaks down into very small pieces, liquid, and gas. The liquid
and the pieces of waste matter run out the overflow pipe to the drain field. The
material that flows out is called effluent. The gas escapes through a vent pipe.
The Tank
The tank must be watertight. If the tank leaks, the liquid level will fall below the
drop pipe, odors will form, flies and mosquitoes will breed, and the soil and ground
water will be polluted. Tanks made from bricks or stone and mortar must be faced
with a coat of rich cement plaster to make sure they are watertight.
The tank can be made of plain concrete sewer pipes 90 or 120cm (36" to 47") in
diameter and sealed at the bottom with concrete (see Figure 11).
Family-sized units should not be less than 1 cubic meter (35 cubic feet), which
will usually allow 6 years or more between cleanings. Thus the family water privy
need not be too deep, which is an advantage in rocky ground where the water
table is high.
The 10cm drop-pipe with its end 10cm below the surface, prevents water from
splashing and improves flushing. Nightsoil may stick in the pipe from time to time
and must be flushed or poked down to stop odors and to keep flies from breeding.
The pipe may be up to 20cm (8") in diameter and reach 20cm below the surface of
the water in the pit, which will prevent sticking, but this size will release more
odors and cause splashing, and the pipe may crust over.
Disposal of Effluent
Disposal of effluent from a family unit is usually done in seepage pits or by
below ground irrigation. The amount of effluent is equal to the amount of
nightsoil and water put into the digesting pit. This averages 4.5 liters a person
each day, but the drainage system should be designed to handle 9 liters a person
each day. When a water tap is inside the privy, the effluent disposal system must
be much larger. Too much water causes poor digestion of sludge.
The area of below ground irrigation ditches or seepage pits needed for a family
of five will be from 1.4 square meters (10.7 square feet) in very light soil to 5
square meters (53 square feet) in soils that are hard to penetrate.
These methods are not practical in regions where the water table rises to within
1m (3') of the ground surface, or in clay soils or swampy land. Here some type of
sand filter may help, but this requires help and approval from local health experts
and continued maintenance.
The first step in putting a new water privy into operation is to fill the tank with
water up to the overflow pipe. Digested sludge from another privy can be added
to the tank; this will seed the water and start the decomposition process. If the
tank is not seeded, it will take about 2 months for the process to get going
efficiently. Once this level of operation is reached, the privy will keep the
process going, provided it is used daily. Cleaning and flushing the slab and bowl
daily with 25 to 40 liters (6 to 10 gallons) will give the tank the small amount of
water it needs to keep the process going.
Removing Sludge
The sludge that forms in the tank must be bailed out before the tank is half-full,
about 6 to 8 years after the privy is put into operation. A manhole, often located
outside the shelter, is made for this job.
Notice in Figure 9 that the tank floor slopes toward the manhole for easier

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cleaning. Both the vent and the drain are easily reached. The drain has a T-shaped
section that helps to keep hard surface scum from entering and plugging
the drain and whose shape makes it easy to clean. The overflow pipe in Figure 10

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is an elbow.
Bury the sludge in shallow trenches about 40cm (16") deep.
Wagner E.G. and Lanoix, J.N. Excreta Disposal for Rural Areas and Small Communities.
Geneva: World Health Organization, 1958.
Philippine Water-Seal Latrine
A water-seal bowl improves a latrine by keeping flies out of the pit and preventing
odors from escaping. The mold described here (see Figure 12) has been made

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and used successfully in sanitary
latrine programs in the Philippines.
The advantage of this mold over a
concrete mold is that it requires no
drying time.
                              Tools and Materials
Wood: 19mm (3/4") thick, 31cm (12 1/2") wide and 152.5cm (5') long
Galvanized iron: 0.75mm x 32cm x 40.5cm (1/32" x 12 1/2" x 16")
Large nails: 18
Cement and clean sand
Galvanized wire: 5mm (3/16") in diameter and 30.5cm (1') long, for interior mold
Bamboo pole or iron rod: 30.5cm (1') long, to position interior mold
Making the Mold
If the materials for the mold are cut according to Figures 13 and 14, the bowl is

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o     Nail the metal sheet around the curved back of the mold (see Figure 12).
o     Attach the two front pieces with large nails through the loose-fitting holes.
      These holes make it easy to remove the front pieces. The extension at the
      bottom of piece No. 1 is important in making sure that the bowl will seal
      well below the water level.
Making the Bowl
Since the mold has no bottom, find a flat place to work where the mold can be
propped against a wall. Fill the mold with a mixture of two parts fine sifted sand
to one part cement.
Use only enough water to make the mixture workable. Pack it in so that there
are no airpockets. Let it set for 15 to 20 minutes until the mixture is stiff. Next,
with a ruler, measure a 38mm (1 1/2") wall around the top and outlet and dig out
the inside with a tablespoon (see Figure 15).

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Keep a straw handy to gauge the
thickness of the walls of the bowl
while digging, because it is difficult
to judge otherwise.
Dig out the large interior first,
then the outlet. The finished
interior of a bowl is shown in
Figure 16.

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Be sure you can insert three fingers vertically, 5cm (2"), through the hole leading
to the outlet. Be careful to release front piece No. 1 by inserting the spoon
around the edges (see Figure 16).
After the interior has been dug
out, the walls will have slumped
down about an inch. Use the
cement taken from the interior to
build the walls back up; then
smooth all exposed surfaces with
the back of the spoon as in Figure 18.

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To be sanitary, the bowl must
be as smooth as possible so that
germs cannot build up in crevices.
For a finishing coat, one of two methods may be used: (1) immediately after
smoothing, sprinkle dry cement over the still wet surfaces and smooth again with
the spoon (Figure 18); or (2) let the bowl set for half an hour and apply a
mixture of pure cement and water-a coconut husk brush is good enough. Either
method gives good results.
For a luxury product, use white or red cement for the finishing coat; several
coats are necessary.
The finished bowl should be left in the mold to dry 48 hours. It can be removed
after 24 hours only if extreme care is taken. Pull out the front nails and remove
pieces No. 1 and No. 2; pull the sides and back away from the bowl.
Making an Interior Mold
Because digging by hand is tedious and because it must be done very carefully to
make the walls consistently thick, it is better and faster to use an interior mold.
After the first bowl has hardened thoroughly, fill the outlet with dry sand so that
the cement cannot flow into it. This would make it impossible to remove the interior
mold when it hardens (see
Figure 19). Line the large interior

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with paper and fill it with cement-a
4 to 1 sand-cement ratio is
good enough. Insert a heavy wire
loop in the top so that the interior
mold can be positioned on the
exterior mold with an iron bar or
bamboo pole.
When an interior mold is used, it is only necessary to dig out the outlet. It is a
good idea to have several interior molds, but not necessary to have one for each
exterior mold. The interior mold should be removed after 15 to 20 minutes so that
the bowl can be smoothed and finished. Then it can be used to make the next
Using the Interior Mold
To use the interior mold, fill the wooden mold about 12.5cm (5") from the bottom
and insert the interior mold in the correct position (see Figure 20). Push the

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cement around the mold with
a stick and pack it well to
get rid of air spaces.
After the molds are removed,
the finished bowl should be
left to dry until it is rock
hard-a week is usually
safe-before delivery.
A sand-cement ratio of 2 1/2 to 1 has been used successfully with the bowls. A
ratio wider than this may make them too expensive. There are many ways to
strengthen cement; experiments may bring a cheaper solution. One possibility is to
add short coconut husk or abaca fibers.
Installing the Toilet
For use in private homes, dig a pit about 1.5m (5') deep and 1m (3') square. The
deeper the pit and the smaller the width the better, since a small slab is cheaper
(see "Pit Privy" Section). It can even be dug under the house-especially in
cities-because the toilet gives off very little odor, unless this position endangers
the household water supply. The pit may be lined or unlined, depending upon the
soil. Hard clay soil need not be lined. But, if the house is near the sea or on
sandy soil, the pit should be lined with, for example, bamboo poles or hollow
blocks as shown in Figure 21.

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Place boards around the outside of the pit 15cm (6") from the edge of the pit to
form the perimeter of the slab (see Figure 22). Place large pieces of bamboo split

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in half across the pit as a base for the slab. Place the bowl between two of the
bamboo pieces with a piece of wood under the front and back; nail these to the
bamboo. After the bowl is positioned in this way, pour water into it to be sure it
will seal off the outlet. The top of the bowl should be 7.5cm (3") above the
bamboo base.
Now put bamboo slats across the pit at right angles to the large pieces of
bamboo, completely covering the pit. Cover this with several thicknesses of
newspaper. Pour cement around the bowl until the slab is about 5cm (4") thick. A
mixture of two parts gravel, two of sand, and one of cement is good. The slab
can be reinforced by placing bamboo slats between two layers of cement. Make
sure that the outer edge of the slab is higher than the bowl and slants towards
the center, so that the toilet can be easily cleaned. Apply a finishing coat of
pure cement to the slab. Many people prefer to add foot rests and urine-guard-there
is room for imagination.
It is extremely important to have an ample water supply at hand. About 1 liter (1
quart) of water is needed to flush the toilet, and people will be discouraged from
using the latrine properly if they have to go some distance for water. It is a
good idea to have an oil drum or a small concrete tank nearby to supply water
for the latrine.
Do not use the latrine for at least 3 days-a week is best-after it is installed.
A pit with the suggested dimensions should last a family of eight about five
years. One person uses about 28 liters (1 cubic foot) a year.
Gordon Zaloom, Peace Corps Volunteer.
Thailand Water-Seal Privy Slab
The Thailand Water-Seal Privy Slab, made from concrete, is useful for large-scale
privy programs. The slab, which includes a bowl and trap, is used to cover an
ordinary pit privy.
Master molds for the bowl and trap
are used to make secondary molds
from which the bowl and trap are
actually made. The master molds
can be made from the plans in the
entry that follows. The master
molds can sometimes be purchased
from local health officers.
The finished slab is quite strong
because its three parts are cast at
the same time (see Figure 10). The

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method described here can be
applied to other water-seal slab
The water-seal trap is curved back under the bowl as shown in Figure 2a. This

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makes flushing more difficult, but prevents erosion of the back of the pit on
loose soil. The same general method could be used to make a forward flushing
trap (see Figure 2b).

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The basic method for making these water-seal slabs is to cast the slab, bowl, and
water-seal trap using three forms:
1.   A wooden form for shaping the slab (see Figure 6).

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2.   A concrete bowl core for shaping the inside of the bowl (see Figure 3).

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3.   A concrete core for shaping the inside of the water-seal trap (see Figure 9).

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                             Tools and Materials
Master molds
Materials for making concrete
Wool for platform forms
Reinforcing rod and wire
Crankcase oil
Beeswax and kerosene (optional)
Steel bars: 19mm x 19mm x 7.5cm (3/4" x 3/4" x 5")
The forms used when making a slab must stay in place until the concrete is
strong enough, usually 24 hours. For this reason, many sets of forms are necessary
if a reasonable number of slabs are to be cast every day. Here is where the
three master molds are needed: one of them to cast the bowl core, and the other
two to cast the trap core (see Figures 14 and 18).

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Casting the Bowl Core
Oil the inside of the master bowl mold and insert a 19mm x 19mm x 7.5cm (3/4" x
3/4" x 3") steel bar into the bottom.
Add a fairly loose mixture of cement and water, called neat cement, to a depth of
about 15cm (6"). Then fill to brim with a 1:1 cement-sand mixture. The 1:1 should
be firm, not runny, and should be laid into the loose neat cement without stirring
to insure a smooth finish on the bowl core.
After the bowl core has become firm enough, scoop a depression into the surface
to install two steel hooks made from the reinforcing rod. They should be about
22.5cm (9") apart, and should not protrude above the surface of the concrete (see
Figure 3).

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Let the concrete set at least 24
hours before removing the bowl
core from the master molds. The
bowl core can be used to make
another master mold and the master
mold can be used to make more
Casting the Trap Core
Add about 2.5cm (1") of 1:1 cement-sand mix to the oiled trap master mold and
put in some wire for reinforcing. Then fill it with 1:1 almost to the brim (see
Figure 4).

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Put the oiled insert mold into place
and scrape off excess (see Figure 5).

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After 45 minutes, remove the insert
and put a square sheet metal pipe
19mm (3/4") high into the cubical
indentation left by the insert. The
pipe is made by wrapping sheet
metal around a 19mm x 19mm (3/4"
x 3/4") steel bar. Let the concrete
dry in the mold for 24 hours.
Remove the finished trap core by
tapping the master mold gently
with a wooden block.
Making the Wooden Slab Form
Make a wooden platform 90cm x 90cm (35 1/2" x 35 1/2") out of 2.5cm (1") thick
planks. This is the base of the form. The finished slab will measure 80cm x 80cm
(31 1/2" x 31 1/2"). See Figure 6.

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Cut out of the platform a hole 10cm x 33cm
(4" x 13") for the hooks of the bowl core to
extend into. The back of the hole should be
28cm (11") from the back of the platform. To
determine the location of this hole, draw the
outline of the bottom of the bowl on the
platform, with the back of the bowl outline
23cm (9") from the back of the platform.
(This is 17.8cm from the edge of the slab, as
shown in Figure 6.) The back of the hole
should be 28cm (11") from the back of the
Using 38mm x 38mm (1 1/2" x 1 1/2") wood, make a frame with inside dimensions
of 80cm x 80cm (31 1/2" x 31 1/2") (see Figure 7).

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Gouge out the footrest with a wood chisel. The inside of the foot-rests should be
about 12.5mm (1/2") from the outline of the bowl.
Casting the Slab
With these three forms finished, you are ready to cast the first waterseal slab.
If desired, coat the bowl core and the trap core with a layer of wax about 3mm
1/8") thick. Prepare the wax by dissolving 1kg (2.2 pounds) of melted beeswax in
0.5 liter (1 pint) of kerosene. Apply the wax with a paintbrush. The wax coating
will last 5 to 6 castings. Wax makes removing the cores much easier, but it is not
absolutely necessary. Let it dry before oiling.
Place the bowl core on the wooden slab form and fill all cracks with clay (see
Figure 8). Oil the bowl, platform, and frame.

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Apply a 6mm (1/3") thick coat of
pasty cement and water mixture to
the bowl core and platform. (Many
people prefer to spend a little more
for an attractive polished slab. To
do this, use a mix of 5 cement: 5
color: 1 granite chips instead of a
mixture of cement and water. After
the forms are removed, polish with
a carborundum stone and plenty of
Cover the bowl core with a 1:2 cement-sand mixture to a total thickness of
12.5mm (1/2"). Make a smooth lip on the cement 10mm (3/8") from the top of the
bowl core as in Figure 9. This lip is your water seal. Use fairly dry cement; let it

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set for 15 minutes before cutting the lip.
Place the trap core on the bowl core and seal
the crack with clay. Also add a little clay on
each side of the form (near the thumb in
Figure 9) to prevent cement from getting to
the front lip.
Cover with 1:2 cement-sand mixture to a
thickness of 12.5mm (1/2"). Do not exceed the
12.5mm (1/2") thickness below the trap core
or you will not be able to remove this core.
Fill the slab form with a mixture of 1 cement: 3 clean gravel or crushed rock
almost to the top. In preparing the concrete, first mix cement and sand, then add
gravel and water. Use water conservatively. The looser the mixture, the weaker
the concrete will be.
Press in 4 pieces of 6mm (1/4") steel reinforcing rod (see Figure 10). Fill to top

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of frame and smooth. Allow at least 24 hours for setting. Remove the frame by
tapping lightly with hammer.
Turn the slab form over on a wooden stand and use simple levers to remove the
bowl core. You must remove the bowl core before the trap core (see Figure 11).

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Tap the trap core gently and slip it out. Add a little water and check to see if
your seal is 10mm (3/8").
Keep the slab damp and covered for a minimum of three days and preferably a
week to gain strength.
Master Molds for the Thailand Water-Seal Privy Slab
This entry describes how to make the three master molds from which cores can
be cast. The cores in turn are used for casting Thailand Water-Seal Privy Slabs.
                              Tools and Materials
Materials for making concrete
Steel rod, 19mm (3/4") square
Sheet metal (tin-can metal is satisfactory)
Reinforcing wire
Oil (used crankcase oil is satisfactory)
Paint brush
It may be necessary to make master molds rather than to purchase them. Study
the entry "Thailand Water-Seal Privy Slab" before starting to make these master
     o    The Master Bowl Molds,
     o    The Master Trap Molds, and
     o    The Trap Mold Insert.
Making the Master Bowl Mold
Enlarge the templates of the bowl outlines on Figure 12 (increase all dimensions

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by one third). Cut out profiles from your larger templates.
Shape a mound of clay using the cardboard profiles as a guide (Figure 13). Form

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a little square pipe, 19mm (3/4") long, of sheet metal on the 19mm (3/4") square
steel rod. Make several of these as
they will be used later when
casting the cores. Fill the square
pipe with clay and press it into the
top of the day mound a little bit.
This will be used later to "key" the
cores together.
Use a paint brush to paint the clay
mound with oil; old crankcase oil is
Cover the clay mound with a stiff mixture of cement and water to a thickness of
12.5mm (1/2"). If the clay mound was properly prepared, the inside finish of the
bowl mold will need no further smoothing.
After this cement has set 30 minutes,
build up the thickness to 38mm (1 1/2")
with 1:1 cement-sand mix. Let this set
24 hours and carefully lift the finished
master bowl mold from the clay mound.
The finished bowl mold is shown in
Figure 14.

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Making the Master Trap Mold
Make cardboard profiles of the trap from Figure 17 as you did above with the

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bowl. Shape the outside of the trap from clay and let it harden overnight.
Shape the under side by hand with a trowel using Figure 15 and the insert profile

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from Figure 17 as guides. Mark the locations for a 19mm (3/4") square metal pipe
by holding the clay trap over the
clay mound used to shape the bowl
mold, and letting the square sheet
metal cube mark the trap.
Insert the sheet metal pipe into the
clay trap and scoop out the clay
from inside (see Figure 15).
Check the clay trap on the bowl mound again to be sure it lines up properly.
Oil the clay trap.
Put a heel-shaped piece of clay under the clay trap and trim the sides. This will
prevent the cement from running under the mold (see Figure 16).

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Cover with cement and water to
19mm (3/4"), add steel reinforcing
wire, and cover with 19mm (3/4")
more of 1:1 cement-sand mixture.
Flatten the top and insert wire
handles. Let it set at least 24
hours. This completes the master
trap mold.
Making the Trap Mold Insert
Turn the master trap mold over carefully and remove the heel-shaped clay plug.
Oil all inner surfaces and fill to the brim with 1:1 cement-sand mix.
Insert a small wire handle and let the concrete set for at least 24 hours before
separating the finished molds.
Figure 18 shows the completed master trap mold and insert.

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Karlin, Barry. Thailand's Water-Seal Privy Program. Korat, Thailand: Ministry of
Public Health.