While you may find that your fence posts are pressure-treated, that's only the beginning of what you should do to slow down the rotting process. While a treated 4x4 may last 10 to 25 years, depending on the wood, the soil, and weather conditions, following the simple steps below could double or triple that number.
Back in 1961, two wood scientists planted treated-lumber posts in the ground of southern Mississippi. Sixty years later, most of those posts are still there—no rot, no fungi, no termites. Their experiment set the official statistical lifespan of treated lumber that the industry refers to today: over 60 years.
If properly treated and installed, pine fence posts can last for 20–35 years; untreated pine posts might only last 3–7 years. chemical in the posts. When large numbers of fence posts need to be installed it is probably most practical to pound them into the ground with a hydraulic post driver, small end first.
Pressure-treated wood will rot in concrete when exposed to wet conditions such as trapped water. In optimal conditions, pressure-treated wood set in the earth may last as long as 40 years. However, when vertically set in a non-draining concrete base, pressure-treated wood may last only a few years.
Pressure-treated wood is wood treated with chemicals to extend its lifetime. Most pressure-treated lumber is preserved with various alkaline coppers. With the right care, pressure-treated wood can last up to 40 years. The main benefits of this material are affordability, durability, and versatility.
Rot is a Real Threat for Any Wood
Pressure-treating can make wood water-resistant, but it's not 100 percent rot-resistant. Any time the wood moves, bends, or cracks, water can enter.
The purpose of pressure treating is to make the lumber rot-resistant, not water-resistant. As a result, pressure-treated lumber will still absorb and shed moisture which leads to expanding and contracting of the post. In a nutshell, the lumber will twist, crack, bend, cup, and ultimately destroy itself.
With pressure-treated posts, the rot will be slow. We have three ways to solve the rotten post problem. First, the posts should be set on top of a bed of coarse gravel 3 to 6 inches deep, so the base of the post is in contact with the gravel. Concrete should be poured around the post - no concrete under the post.
The best recommendation for setting fence posts of any kind is to always secure all metal fenceline poles in cement, plus all wooden corner and gate posts as a minimum. Doing so creates a footer that prevents the post from rising out of the ground or leaning for any reason.
A fence is only as strong as its posts. The American Standards for Testing Materials (ASTM) suggests always setting fence posts in cement. One of the most important reasons your fence posts should be set in concrete is to keep them plumb and level over time.
Next, pour an additional three inches of gravel into the hole, tamping down a second time. This simple measure goes a long way toward helping rainwater drain freely into the subsoil. It works so well, in fact, that in mild climates, builders sometimes elect to set fence posts with gravel alone.
Slow the Wood Rot
While a treated 4x4 may last 10 to 25 years, depending on the wood, the soil, and weather conditions, following the simple steps below could double or triple that number. By comparison, an untreated wood fence post may need replacing in as little as five years.
Place your fence post on top of the gravel drainage layer and fill the rest of the hole in with soil, ensuring it stands firm and steady. As an alternative, Postsaver sleeves are a cost-effective, simple way to keep wood rot at bay.
Placing a thick layer of loose gravel at the bottom of the post hole will allow groundwater to trickle through the rocks and down away from the base of the post. This will prevent the post from rotting by keeping it constantly dry. You can purchase gravel at a local hardware store or landscaping-supply business.
Pressure-treated wood is softwood lumber, typically southern yellow pine that has been chemically treated to resist rot, decay, and termites. All treated wood is now “ground contact”. “Ground contact” has a high chemical retention level and can be placed directly on or in the ground.
It will not last long (7 yrs max) if the bottom of the post is wet. If you place stone at the base of the post, it should last 20+ yrs. The length of time will also depend on whether it has been cut after manufacture or not as well.
It doesn't matter if it is a do-it-yourself (DIY) project or a professional installation, wood fence or vinyl fence, your fence posts should be set in concrete. Without a properly set concrete footer, your fence posts will begin to sag until they eventually fail.
Postsaver® is the number one choice for preventing fence post rot because it will literally block rot. It is a heat-shrinkable outer sleeve that fits over the base of the fence post. The sleeve has a thermoplastic bituminous interior liner, which seals to the wood.
Wood on Concrete or Other Masonry
Water can pass through porous materials vertically via capillary action. When you have a vertical wood post or column resting on concrete or other masonry, and that concrete/masonry itself rests directly on the earth, then the post/column must be pressure-treated.
While expanding foam can secure posts for lightweight fences such as vinyl or wire mesh, it's better to go with concrete for structural posts, such as posts for porches, decks, or large and heavy gates. Expanding foam is not as strong as concrete when supporting load-bearing posts.
Wood in direct contact with concrete, and the dampness often found there, will rapidly decay. To avoid this, use pressure-treated lumber. This is wood impregnated with decay-resisting chemicals, usually chromated copper arsenates.
The depth of the hole should be 1/3-1/2 the post height above ground (i.e., a 6-foot tall fence would require a hole depth of at least 2 feet).
You can choose to use a water repellent sealant to your wood to help keep rot-causing moisture out from your fences. Additionally, you can potentially mix a sealant and a stain to protect both the wood and the colors from moisture accumulation.
For fence posts, cedar can go several years without rotting; however, they tend to be less durable against soil erosion than pressure treated pine posts.