Agricultural Structures and Environmental Control 3(2+1)

LESSON 8. Construction of Farm Fencing

Upright posts:

Upright posts made of wood are cheaper but does not last long.  They become uneconomical due to painting of them year after a year and renewing owing to white ants, rot and deterioration.  Next in order of present day popularity for fence post is iron, which also has to be continuously painted and guarded against rust, which is the ever present enemy of iron material.  The concrete posts are better than both wooden and iron ones and durable though the cost is slightly more than other two.

The concrete posts can be manufactured on the farm itself.  They are made as square posts, square tapered posts or as posts with triangular coping.  Concrete posts are easy to construct.  The posts are usually made for 1.8 m to 2.1 m (6 ft. to 7 ft.) length and the size of the posts being 12.5 cm square (5 inches) square or 12.5 cm square (5 inches square) bottom and 7.5 cm square (3 inches square) at top.  These posts are made on the form by using rectangular wooden moulds without top or bottom.  The moulds are placed over a platform and reinforcement bars (steel rods) are placed in position leaving a cover of 1.9 cm to 2.5 cm (3/4 inch to 1 inch) alround by propping.  The size of rods adopted for reinforcements may be of 6 mm or 10 mm (1/4 inche or 3/8 inch).  The smaller diameter rods are adopted for ordinary posts,  but when heavy usage is expected and a bigger post is therefore necessary, larger diameter may be used.  As a fence post has usually to resist lateral or bending pressure and it is difficult to determine from which direction the pressure acts, it is safe to reinforce all the four sides.

Fig. 6.2.  Cross section of concrete post with reinforcement.

The rods are laid lengthwise, the ends built up at right angles to exclude any change of the concrete pulling away from the steel.  The rod should be kept apart by 3 mm (1/8”) wire wound round in the form of spirals at 30 cm (12 inches) apcing.

Casting posts :

The concrete is prepared by mixing broken stones 1.9 cm (3/4 inches gauge with sand and cement in the proportion of 4:2:1 or 3: 1.5:1 by volume.  This is mixed well by adding clean water at the rate of not more than (5 gallons) pr bag of cement.  The mixture after the water is added should be of medium wetness and thoroughly plastic, but not too slopy.  Before concrete is placed in the mould ; the latter should be lightly greased or rubbed with oil or soft soap.  Instead, they can be thoroughly wetted by pouring water.  The concrete should be placed within the mould as soon as mixing is completed as the concrete sets within 30 minutes.  The mixture filled in thin layer should be tamped well to ensure complete filling of the space without any voids.  The top surface should be trowelled to level the surf ace and left to settle.

Fig. 6.3. Mould for Post.

If holes are to be provided for inserting the wires or to be tied, rods should be inserted through the holes provided in the side of the boxes before the concrete is placed.  These rods should be withdrawn after the concrete has set sufficiently to retain its shape which varies from 4 to 6 hours.

The castings should be left in the mould for 24 hours after which time the mould can be dismantled are reused.  Then the post should be cured on the platform itself for 4 days by covering it wetted sand.  It is then lifted from the platform and put in a water tub or pond for curing.  If no pond is available it can be placed over a bed of wet sand and water sprinkled on it.  The curing should be done for two or three weeks.  The posts should be used preferably after 3 months period after casting but in no case it should be used before 30 days.

Spacing of posts:

The life of fence and maintenance cost is dependant upon the size of spacing of fencing posts.  usually a spacing of 2.4 m to 3.0m (8 ft. to 10 ft.) is better for wire fences. The corner posts and straining posts should be heavier than the line posts and must be supported by struts.   For this a mortise is made near the top of the post.  The struts are made to 7.5 cm x 7.5 cm(3” x 2”) and reinforced with four 6mm (1/4”) diameter rods.  The struts are placed into the ground and covered by concrete.

Fig. 6.4. Barbed wire fence showing upright and strut.

Erecting fence posts and wire:

The posts should be set in the ground for 52.5 cm (1.75 ft.) or 60 cm (2 ft.) depth and should be concreted with a mix of 1:2.5:5.  The wires are fastened to the posts and stretched well.  The different methods of fastening the wires to the posts are given in fig.

Fig. 6.6. Woven wire fence.

The selection of wires depends on the purpose for which it is used.  Barbed wire is effective for fencing the boundaries to prevent animal trespassing.  But it is not suitable for poultry yards.  Plain wires are best suited for cattle yard with or without barbed wire.  Wire mesh is suitable for poultry yards.  In fencing with barbed wire, plain wire or wire mesh, the arrangement of horizontal wires at the bottom should be closer than at the top.

Farm gates :

Gate and position should be selected so that unnecessary travel distance should be reduced.  The gate way should be wide enough to give access to easy traffic.  The gates provided should be strong and durable.  For farm gates separate gate pillars of heavier sections should be provided to bear the weight of gates.  The gates may be wooden, or iron with necessary locking arrangements. Some of the simple type of gates that can be made in the farm itself is given in figure.

Fig. 6.7.  Simple farm gates.