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Line posts
Line posts provide additional support for the wires in a fence. They keep the wires at the required height and evenly spaced. Line posts are set at intervals between the strainers.
Like strainer posts, line posts are made of timber, steel or concrete. The material chosen for posts on a property will depend on cost, availability and durability. The posts will be in the ground for a very long time. Wood rot, termites, corrosion from acid or saline soils, weathering and fire all contribute to the failure of posts and hence fences. The fence shown below uses both timber and steel posts.
Hardwood posts should be selected from timber that grows in the area and is known to be durable in the ground. Posts treated with copper chrome arsenic (CCA) withstand both rot and termites but are not fire resistant. The ashes of burnt treated posts contain arsenic that is toxic to livestock. A new post treatment has been developed that contains a fire retardant.
Steel or star posts do not rot or burn and are not eaten by termites. However they do corrode, especially in coastal areas and in acid or saline soils. Black varnish and galvanising treatments are used to lengthen the life of steel posts in the ground. Concrete posts are expensive and usually used only in fences built for government contracts (right). Although more durable than other materials, concrete posts can weather and crack or fail due to overstraining wires.
The typical Australian cattle fence used to be a rigid structure with wooden posts set at close intervals of three to four metres or less. These fences used large numbers of posts and are now considered very expensive to erect in terms of materials and labour. Cattle tend to rub and push against the posts, eventually causing them to fail.
An alternative that is growing in popularity is the suspension fence. The posts are set much further apart and high tensile barbed wire is strained in long spans. Droppers are used in suspension fences to keep the wires evenly spaced and supported. They do not touch the ground or hold up the wires. Made of wood, wire, steel, polythene or fibreglass, droppers also increase the visibility of the fence.
When cattle push against suspension fences, the wires give and move under pressure with little or no damage. Cattle prefer to push against immovable objects and they learn to keep away from these fences.
Suspension fences are more common on flat or gently undulating country. They are less practical in coastal or other areas where the terrain is uneven with numerous gullies and ridges.
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