Old fences need to be replaced because of age however think before you decide to change it. Even though the boards are discolored and some are partially disconnected from the rails, the fence may still have years of life left. You may have to replace some rotted posts to straighten the fence and you may have to reattach some of the pickets, but it isn’t difficult to return the wood to something close to its original color. Restoring your old fence as an alternative to replacing it can save you hundreds of dollars.
Prop up the fence around a rotting post by wedging lengths of 2-by-4-inch lumber under the top rails and screwing them to the rails with 2-inch exterior screws. Cut the lengths of 2-by-4 so that the fence stands reasonable straight.
Disengage the fence from the rotted post by pulling the nails out with a hammer and pry bar, or removing the screws with a drill. When the post is free, work it out of the ground or cut it off at ground level with a hand saw and dig out the part that remains in the ground with a shovel. If the post was set in concrete, dig out the entire mass of concrete.
Measure the distance from the ground to the top of the new post. It will extend the same distance above the top of the fence as all the other posts. Dig out the hole for the new post to a depth of one-third of this distance. Cut the post from 4-by-4-inch pressure-treated lumber and drop it in the hole.
Backfill the hole with gravel or concrete mix, adding the backfill material incrementally as you check the level of the post with a spirit level. When the hole is filled to about a distance of 2 inches from the top, lay on concrete mix to form a small mound around the post so water will run away from it.
Let the concrete set for 24 hours, then reattach the fence to the post with 2-inch exterior screws. Replace all rotting posts in the same way to straighten the fence.
Reattach separated fence boards or pickets to the rails with 1 1/2-inch exterior screws. Drive the screws into sections of the rails that aren't rotted.
Wash the fence with a pressure washer. If the wood is moldy or extremely discolored, add deck washing detergent to the water, if your washer has the capability for it. If it doesn't, mix the detergent with water according to the specifications on the container and spray it on with a garden sprayer. Wash it off with the pressure washer.
Let the fence dry for three days to a week, then spread on a coat of clear finish or stain with an airless sprayer or a paintbrush.