If you recently had a new wood fence installed in your back yard, you might have noticed something strange over time: the fence posts may have developed cracks or splits. This is a common issue across the industry with pressure treated posts, and while it can seem a little worrying, it’s not as big a deal as you may think. In fact, cracking is just part of the natural process of how wood seasons and drys out, and it doesn’t usually affect the integrity of your fence. But why does this happen, and what can you do about it? Let’s crack this one open!
What Are Pressure-Treated Fence Posts?
Pressure treated wood is a softwood that’s been treated with a copper based chemical to make it last longer and resist things like rot and moisture. This treatment process helps keep the longevity of the wood, especially since its used outdoors, where the posts are exposed to rain, sun, dirt, moisture, changes in temperature and other elements of mother nature.
Pressure-treated fence posts are made from softwoods like spruce, which is generally cheaper and easier to work with. Spruce is the common lumber for fence posts, but it’s important to understand how pressure-treated wood behaves, especially when it comes to drying out after installation.
Why Do Pressure-Treated Fence Posts Crack and Split?
Wood is a natural material that contains moisture, and is susceptible to changes in temperature and humidity. Pressure treated wood posts are not kiln-dried, which means they still contain a lot of moisture when they’re installed. Pressure treated wood starts off as spruce, pine or fir lumber, gets treated, then gets kiln dried. However, during the drying process in the kiln, some of the pressure treatment is lost in the lumber. Since fence posts, typically 4x4s and 6x6s, are usually installed below grade, they skip the kiln to maintain the maximum amount of treatment.
Here’s why this causes cracking and splitting:
1. Moisture Loss After Installation
Since fence posts are not kiln-dried, it retains more moisture after it’s installed. But as it sits outside in your yard, exposed to the sun and warmth, the moisture begins to evaporate. The wood shrinks as the moisture leaves, and this can cause the wood to crack or split. This drying out process is completely natural, but it’s what leads to those cracks you might see on your fence posts.
Think of it like a sponge that’s been soaking up water. When you take it out of the water, the sponge will start to dry and shrink. As it shrinks, it may crack or become misshapen. The same thing happens with fence posts—it dries out, it shrinks, and may crack as a result.
2. Environmental Changes (Temperature & Humidity)
Wood is very sensitive to changes in temperature and humidity. When it’s hot and dry outside, the wood loses moisture more quickly. When it’s cool and damp, the wood can absorb moisture, causing it to swell. This constant back-and-forth of the wood expanding and contracting can cause it to crack or split.
Pressure-treated wood, especially when it’s not kiln-dried, is even more likely to shrink and crack because it retains more moisture to begin with. The drying process happens faster and more visibly, leading to more splits and cracks, especially on the sides of the posts.
3. Natural Behaviour of Wood
Even though your fence posts are pressure-treated, the wood is still a natural material. Spruce, which is commonly used for fence posts, is a softwood, meaning it’s not as dense or hard as hardwoods like oak or maple. Softwoods like spruce are more likely to develop splits and cracks as they shrink and dry out. This is simply how softwood behaves over time.
No matter how well-treated the wood is, it’s still vulnerable to moisture changes, temperature fluctuations, and the natural aging process of wood. Pressure treatment helps prevent things like rot, but it doesn’t stop the wood from drying out and cracking.
Is Cracking a Problem for Fence Posts?
You might be wondering if cracks in your pressure-treated fence posts are a serious issue. The good news is that cracking doesn’t usually affect the strength or integrity of the post. In fact, most cracks you’ll see are simply surface cracks, meaning they don’t go all the way through the post.
Here’s why you don’t need to worry too much about the cracks:
1. Cracking Is Usually Cosmetic
The cracks you see on pressure-treated fence posts are mostly superficial. They don’t go deep enough to weaken the structure of the post. Think of it like a scratch on a car—while it looks a little bad, it doesn’t mean the car is falling apart. The post is still strong and doing its job of holding up the fence.
The inside of the post is still intact and able to support the weight of the fence, even if the outer surface has some cracks. So, while it might look a little weathered, it doesn’t mean your fence is unsafe.
2. Pressure-Treated Wood Remains Durable
The pressure-treated chemicals help protect the wood from things like rot and moisture, which can weaken untreated wood over time. Even with cracking, the wood is still more durable than untreated wood. So, while the cracks may make your fence look old or weathered, it’s still going to last much longer than untreated wood would in the same conditions.
3. Wood Still Handles Stress Well
Despite cracks or splits, the wood is still strong enough to do its job. The posts are still holding the fence in place, and the cracks don’t affect the load-bearing capacity of the wood. Wood is incredibly strong, and even when it has a few cracks, it can still withstand the forces of wind, weather, and pressure.
Can I Prevent Cracking?
Unfortunately, there’s no way to completely prevent cracking, as it’s just a natural part of how wood behaves. However, there are a few things you can do to help slow down the process and protect your fence posts a little longer.
1. Seal the Posts
One way to protect your fence posts is to apply a protective sealant or stain soon after installation. Sealing the wood can help reduce moisture loss and keep the wood from drying out too quickly. While it won’t stop cracking entirely, it can help slow the process and give your fence a longer lifespan.
2. Regular Maintenance
You can also extend the life of your fence by maintaining it regularly. Check for signs of wear, like cracks, loose boards, or insect damage. Reapply stain every few years to keep the wood protected from moisture and the elements.
Conclusion
Cracking and splitting in pressure treated fence posts is a natural part of the wood’s behaviour. Since the wood is not kiln dried, it retains moisture when installed, and over time, as that moisture evaporates, the wood shrinks, causing it to crack or split. This is especially common in softwood like spruce. While it might look a little weathered, these cracks don’t usually affect the strength or integrity of the fence posts. The posts are still strong enough to hold up the fence and keep your yard secure.
Cracking is something that happens with most wood used outdoors, and it’s not something to panic about. If you want to help reduce cracking, you can seal the posts and maintain your fence. But at the end of the day, pressure-treated wood is still one of the best choices for long-lasting, durable fence posts.
So, don’t stress about a few cracks—they’re a normal part of wood’s natural aging process, and your fence will continue to do its job for many years to come!