Preservative should only be applied to dry timber.

Unless fences are made of a natural rot-resisting timber, such as cedar or oak, you will also need to treat them regularly with a wood preservative. Re-apply solvent-based products every two or three years and water-based preservatives or creosote every four years.

Creosote

Creosote is an effective and widely used treatment for preserving fencing. However, it has a very powerful smell, which many people may find unpleasant. It is also poisonous if inhaled, swallowed or absorbed through the skin, so you must wear protective clothing when applying it. For this reason, creosote is not recommended for fences used to support plants.

Water Based Preservatives

These are much less toxic to plants and less unpleasant to use. They prevent the growth of surface moulds and improve the appearance of the timber. However, they are generally less effective at controlling rot.

Wood-Pitch Preservatives

These preservatives create a barrier that prevents water penetration, making the wood too dry for bacterial action.

Repairing Support Posts

One of the major problems that develops as a fence ages is broken timber support posts. If the damage is at soil level, the most effective way of repairing is by using a concrete spur - this is a short post sunk into the ground alongside the existing one and bolted to it to give support.

1. Dig a hole 45-60 cm (18-24 in) deep around the damaged post and saw off the rotten part.
2. Paint the cut end of the timber post with a wood preservative.
3. Place the concrete spur in the hole, resting it against the post, and pack hardcore around the base to support it.
4. Push bolts through the holes in the spur and tap them with a hammer hard enough to leave an impression on the wooden post.
5. Remove the bolts and spur and then drill holes through the post for the bolts.
6. Bolt the concrete spur onto the post, tightening the nuts from the spur side so that the wooden post is not damaged.
7. Make sure that the post and spur are vertical, if necessary bracing them in position temporarily with stakes driven into the ground.
8. Fill the hole with a fairly stiff concrete mix tamping it down firmly to remove any air pockets.
9. Once the concrete has set (after about a week), remove the supporting stakes and saw off any surplus length from the protruding bolts.

Repairing Arris Rails

Broken arris rails can be easily repaired with specially angled metal brackets. These can be found in designs either to support a rail that has rotted where the end fits into the post, or to brace a broken rail in the middle. Both styles are simply screwed into place.