I haven’t even seen your wood fence and I know that it cost a lot of money to install and took a lot of time and effort to put in. You’re going to want that fence to last at least until you draw your dying breath, and preferably beyond.
You’re not likely to achieve that dream, no matter what wood you use. This post, however, will show you how to protect your wood fence from rotting so you can push back the day you need to replace it as far into the future as it is possible to push it.
What Exactly is Rot and How Does It Affect Wood Fencing?
You might think rot is rot, but it’s a bit more complex than that. There are actually two different kinds of wood rot and each form of rot will impact your fencing differently and need to be treated differently if you find it.
The two types of rot to look out for are wet rot and dry rot. Both are caused by fungi that eat at wood and cause it to decay, much like they would with a dead tree in a forest environment.
Wet rot is the result of prolonged contact with moisture. Water damage can occur because of rainy, damp conditions or other environmental factors, but fences also come into long-term contact with moisture through damp soil, through rain pooling on the tops of fence posts and rails, through snow piling against fence boards and even through wet vegetation sitting up against a fence.
When your fence is struggling with wet rot, it will show some or all of the following forms of damage:
- soft or spongy sections
- wood that’s warped or cracked or that crumbles away
- mushrooms and fungi sprouting from your fence
- a musty or moldy smell
Dry rot, on the other hand, can happen with excessive sun exposure and heat, including hot wind. Over time, this exposure will break down any protective oils or treatments in the wood, leaving it open to fungal growth that will degrade it.
Be on the lookout for these signs of dry rot:
- cracks and wood shrinkage
- sections of the fence that crumble when touched
- damage that looks like termite, ant or pest infestation, but without the actual bugs or passageways
- brown discolouration
- mycelium strands that look like spider webs
- fuzzy white patches or mushroom growth
Now that you know what rots wooden fencing, let’s get into how to avoid it.
How to Resist Rot While Building a New Fence
There are several effective ways to start to prevent rot even before you put your fence up. Here are some general guidelines that will extend the life of your fence.
Choose Rot-Resistant Materials
Use a hardy type of wood for your fencing project. White or Western red cedar, redwood, teak, cypress, black locust and Ipe are all rot resistant and resistant to insects. You can expect to pay a premium for redwood and teak and possibly for cypress, depending on where you live, but you might recoup that cost by not having to replace the lumber as often.
Pressure-treated wood such as pine or Douglas fir is the go-to alternative if rot-resistant wood is hard to come by or if you’re working within a budget. This wood has been preserved in a pressurized tank that forces preservative chemicals into the wood’s interior to make it resistant to water, fungus, insects and decay.
Chromated copper arsenate (CCA) was a standard preservative until it was discontinued for residential use. Now, the most common compounds used to treat wood include sodium borate (SBX), alkaline copper quaternary (ACQ), micronized copper quaternary (MCQ) and copper azole (CA).
These compounds will leach into the soil over time and while the EPA regularly reviews them for safety, many organic gardeners won’t use them. They’re generally not considered safe for aquatic ecosystems, which should be a consideration for you if your fencing project is close to a wetland.
You can find more environmentally friendly alternatives, however, at least for the above-ground portions of your fence. Over at Rise, Tom Saxton has an informative piece on carbon-based pressure treated wood that’s worth a read.
Choose the Right Kind of Wood for the Right Environment
Natural materials always have their own unique benefits, and learning all you can about different types of wood will go a long way towards finding the right one for your project.
Pressure-treated lumber, for example, is ideal for posts because it’s slower to decay than other options. Ipe, cypress and redwood are great types of wood for locations where termites and insects are an issue because their natural oils repel pests.
Cedar can handle moisture and insects and excels in a range of climates. Pine can be a good choice in climates that experience harsh weather extremes because it resists shrinkage and is therefore less prone to cracking.
Finally, consider the grade of the wood. Grades of wood are extremely complex, but in short, higher-grade lumber makes for a longer-lasting fence. Look for clear, premium, select or appearance and construction grades.
Steer clear of lower grades like standard, utility and economy. It’s not just that they don’t look as good—they’ll contain defects and will undermine the structural integrity of your fence.
Prep the Fence Properly
In his book Wooden Fences, carpenter George Nash recommends ensuring that the wood for a fencing project is dry, particularly for wooden posts. Green wood (i.e. wood that’s been recently cut) is moist wood, and it will rot more quickly when underground. It’s also less able to absorb any stains or preservatives you apply than dry wood is.
Nash writes that green fence boards can also “split apart around fasteners and cup and twist off their rails,” as they dry, all of which can give water opportunities to infiltrate the fence and encourage decay.
Regrettably, the drying period for green wood is a long one—sometimes a few months, depending on how green the wood is and what your climate is like. Although lots of property owners and plenty of fence contractors put up fencing green, Nash advises buying wood that’s marked KDAT, or “kiln dried after treatment” for best results.
You can apply a copper naphthenate preservative to the bottoms of wooden fence posts to give them better resistance to rot. Work the treatment a third of the way up the fence posts—it should cover the portion of the post that will end up underground, plus some length to spare.
To apply, brush the product on, repeating coats once an hour until the product stops saturating the post. Don’t forget your protective gear!
If you’re working with pressure-treated wood, choose stainless steel or galvanized nails, connectors and other fasteners—treatments that include copper are corrosive to aluminum.
Stain posts and boards with an oil stain first, before you install them. Fences will rot faster where the posts and boards meet, as water is likely to get trapped in those places. Since those spots will be hard, if not impossible, to reach with a brush or sprayer once the fence is up, staining first will give them some measure of protection.
Think About Drainage
Consider filling your fence post holes with gravel or crushed rock rather than dirt or concrete. Soil will hold moisture against a wood fence post and promote rotting.
Concrete, too, can actually promote rotting. Since wood will shrink and expand with changes in seasons and humidity levels, a gap can form between the post and the concrete. When it rains, this gap will trap moisture against the post since it won’t have anywhere to go.
Gravel and crushed rock, on the other hand, will allow water to drain away from the posts. Gravel isn’t an ideal solution for soils that are loose, since the gravel can shift, but for heavier soils, it can provide a strong base while reducing the risk of rot.
If you do want to use concrete, caulk between the post and the footing to seal any gaps that might form. Make the top of the concrete footings sloped or rounded, as well, so water can drain away instead of pooling on top.
When the hole is completely backfilled, you can cover the hole with soil if you want a more finished look. Try to avoid direct contact between the soil and the post, however. Whether the top of the hole is soil or gravel, bank your medium up towards the post to create a slight slope that moisture can run off of.
When you cut the tops of your fence posts, cut them at an angle, as well, to encourage run off. Flat tops will hold a lot of moisture.
Maintenance Tips and Tricks
Proper maintenance is a sure way to keep your fence looking better for longer, regardless of the type of materials you’ve chosen.
Inspect your fence regularly, especially if it’s exposed to harsh conditions. This is a boring job, but it will let you identify problems early and fix them before rot can spread.
Keep the fence clean. Weed whack along the base of your fence to prevent undergrowth from sitting up against it. Once a year, power wash the fence to remove dirt, lawn clippings and vegetation.
If you don’t have a pressure washer or power washer, give the fence a good cleaning as part of its annual maintenance. Cleaning gets rid of dirt and organic material that can stick to the fence and prevent the air flow necessary to keeping the wood healthy.
If you spot mold anywhere on the fence, treat it by scrubbing the affected area with vinegar. Vinegar is an antimicrobial, antifungal substance that kills mold spores without harming the surrounding grass and plants.
Cracks will naturally form in the wood of your fence over time. When you see them, treat them by brushing them with copper naphthenate or another wood preservative.
Stain every 2-3 years—more if the environment is challenging. This can be a huge job, but you can test if the fence needs staining before you commit to it. One good way to test your fence is to spray a post or rail with water. If the water beads, the stain is still working like it should. If it doesn’t bead, it’s time to restain.
Fence Repair Tips
“Fence problems that are ignored don’t go away,” says George Nash, “they get worse.”
If you spot signs of rot, they need to be addressed right away so you can keep your fence in its best condition. The good news is that unless the rot is extensive, you probably won’t need to replace the whole fence. You can keep rot from spreading by treating or replacing affected sections.
Test your fence posts for rot by digging down a few inches at the base of the post and checking the wood for sponginess. If the wood feels soft, dig around until you uncover the entire extent of the affected area.
Poke something sharp into the post so you can determine how deep the rot goes. Nash suggests that if the rot is less than ½ inch deep, you can scrape the rotten wood surface away and treat the fresh wood underneath with a water-repellent sealant before covering the bottom of the fence post up again. If the rot is deeper than ½ inch, however, you’re going to need a new post.
You can perform similar repairs to the top end of the post. Cut out any damaged areas that feel spongy and treat with a preservative to keep moisture from infiltrating the interior of the post.
The team at This Old House offers this in-depth video demonstrating how to replace an entire post:
Fasteners and Hinges
Fasteners and gate hinges tend to become loose over time because of the way wood shrinks and expands with changing moisture levels. These loose fasteners can become prime sites for rot to take hold.
It’s tempting to simply nail or screw the originals back in to keep components like gates, fence rails and pickets tight and square, but that’s not the best way to resecure them because it’s simply not likely to work long-term.
Instead, remove loose nails and screws. Treat the holes with liquid wood preservative. If the surrounding wood is in good condition, use nails or screws that are slightly larger than the originals to refasten the component. If the area around fasteners is damaged, treat it with wood preservative and find a new spot for nails, screws or hinges.
Pickets and Fence Panels
For painted fences, keep an eye out for peeling and flaking, which are signs that moisture has gotten underneath the paint. Use a wire brush to remove paint flakes and then give the now unprotected wood a quick sanding before giving it a fresh coat of paint.
Pickets or panels that show signs of rotting will likely show those signs near the bottom part, where they come into contact with vegetation and snow mounds. Since pickets and panels are the thinnest component of your fence, rot can more quickly eat through them to the point where trying to scrape away the rot won’t be effective.
The good news is that pickets are also cheaper and easier to work with than fence posts, so it’s usually simpler to replace them. You can pry them off and then pull out or cut down any nails or screws that remain. Paint or stain the new pickets first, then hang them, making sure you avoid the old nail or screw holes.
This short video from Mother Daughter Projects gives a great quick overview of replacing fence pickets:
And this tutorial from Fixit Fallows walks you through fence panel repair:
If you have rails that are loose, you can resecure them to the post with a galvanized steel T-brace, or even use a small wooden block to support the rail. Treat and stain the block prior to applying it, and once it’s ready to go, screw or nail it into the post, just below the fence rail.
If the rails have pulled free already, there’s a good chance that rot has seeped in, so treat the end of the rail by brushing or spraying on a wood preservative. Then secure the rail to the post again, either with a small piece of wood or T-brace as outlined above.
Simply Works shows you how to repair fence rail ends in a few simple steps, without replacing them:
We hope these tips help you build a fence that will stand the test of time and keep on top of the regular maintenance it will need so you can keep your fence lines in tip-top shape over the long run.