How do I make a wood fence last longer?

A wood fence lasts longest when it stays dry and stays finished. The two things that end most fences in Virginia are rotting posts at the ground line and boards that stay wet at the bottom, so most of the work is about water: what the posts are made of, what touches the wood, and whether there is a finish slowing water down. A yearly walk-around and a fresh coat of stain every few years do the rest.

Start with the posts

A fence lasts about as long as its posts. The Forest Products Laboratory says wood in structures fully exposed to the weather, such as decks and fences, and particularly the parts in ground contact, needs preservative treatment to protect it from rot and termites.^[1] The difference is large: Virginia Cooperative Extension's figures give treated southern pine posts 25 to 30 years and untreated southern pine 3 to 7.^[4]

Not all treated lumber is rated for burial. UC4 is the use category for wood in ground contact outdoors, and UC3 is for above-ground use,^[2] so check the end tag on any post you buy or that a contractor delivers. If you cut a treated post or board, brush copper naphthenate (1% to 2% copper) onto the cut surface,^[2] following the product label.

How a post is set matters too. QUIKRETE suggests a gravel base under each post and a concrete top that slopes away from the post to protect it against rot.^[5] Concrete that is dished around the post, or soil piled up over the footing, holds water against the wood at its weakest point. How to set a fence post in concrete covers it when a post needs replacing.

Keep water off the bottom

Rot needs wet wood: serious decay happens only when wood is wetter than its fiber saturation point, which averages 30% moisture.^[3] The bottom of a fence gets that wet for weeks at a time if anything holds water against it.

• Leave a gap under the boards. Pickets that touch the soil wick water up through their end grain.
• Keep mulch, soil and leaves back. Landscaping beds are often built up against a fence over the years until the bottom rail is buried.
• Aim sprinklers away. A sprinkler that hits the same boards every day can rot that section years ahead of the rest.
• Move water away from the line. Extend downspouts that empty toward the fence and fill low spots where water pools.
• Let air through. Vines and dense shrubs growing into the fence keep it shaded and damp.

Why a wood fence rots at the bottom goes deeper into how to read the damage once it has started.

Finish it, then keep it finished

A finish does not stop rot on its own, but it slows water getting in and protects the surface from sun. The Forest Products Laboratory's service-life figures for exterior finishes are a useful guide:

• A clear water-repellent preservative lasts 1 to 3 years.^[1]
• A lightly tinted clear finish lasts 2 to 3 years.^[1]
• A semitransparent stain lasts 4 to 8 years on saw-textured or weathered wood.^[1]
• Solid-color stain lasts 6 to 15 years.^[1]
• Paint lasts 10 to 20 years.^[1]

Two coats of semitransparent stain may last 10 years on saw-textured wood,^[1] while one coat on new smooth wood lasts only 2 to 4 years.^[1] For most fences, semitransparent stain is the practical choice. Semitransparent stains do not form a surface film, so they will not blister or peel even when the wood gets wet,^[1] and a recoat is a brush job, not a scrape-and-prime job.

Paint lasts longer on paper but is harder to keep on a fence. Paint tends to crack where two pieces of wood meet, water gets in through the cracks, and the film then slows the wood's drying until it is wet enough to decay. The Forest Products Laboratory notes that paint failure of this kind usually occurs on painted fences and porch railings fully exposed to the weather,^[1] and priming the end grain helps keep the wood dry.^[1] Whatever you use, treat the end grain. Water-repellent preservatives soak readily into end grain and can slow water absorption there for years,^[1] so brush them onto board bottoms and post tops before the stain.

Watch for the signs it is time: bare wood showing through, water soaking in instead of beading, and grey or black blotches. The Forest Products Laboratory says mildew growth on the surface usually means it is time to refinish.^[1] How to stain a deck walks through the same prep and application, and most of it applies to a fence.

Keep the hardware tight

Loose boards rattle in the wind, split around their nails and let water into the holes. Galvanized screws are one option for fastening boards,^[4] and nails with grooved shanks are less likely to pull out of fence posts.^[4] Fix a sagging gate early, before it drags the latch post over.

If your fence is older

Wood treated with chromated copper arsenate (CCA) was used in residential structures such as decks and playsets before 2004.^[6] EPA does not require removing it, and says a penetrating coating such as an oil- or water-based stain applied regularly may reduce the leaching of chemicals.^[6] When you work on it, wear goggles and a dust mask when sawing it, wash your hands after handling it, and never burn it at home.^[6]

Stop and call a pro if

• Posts are soft at the ground line or the fence is leaning. Replacing posts means digging, and Virginia law requires a locate request before any excavation.^[7]
• You find termite tubes or hollow, tunnelled wood behind a firm surface.
• The fence is a swimming pool barrier or sits on a retaining wall.
• A long run needs boards and posts replaced at once.

If you hire it out, a Class C contractor's licence covers single contracts over $1,000 and under $30,000,^[8] so check the business with DPOR. See how long a wood fence lasts, browse fence repair businesses, exterior businesses around Blacksburg, or all exterior answers. To have it repaired or refinished, describe your fence once and local businesses send written quotes.