How Long Does Ground Contact Wood Last?

Wood lasts long as long as you preserve and protect it from harmful elements. Even better, pressure treated wood is more durable and lasts years upon years. It has preservatives that keep it resistant to pests and moisture. However, underground conditions vary significantly from those above the ground. And most woodworkers newbies and experts still ask, how long does ground contact wood last?

You can expect the ground contact wood to last about eight to twelve years. However, the duration can lengthen or shorten depending on the wood’s location and type. Also, how well you preserved lumber before burying it affects how long it will stay intact in the ground.

That said, let us get into an in-depth discussion on ground contact wood and how it works. Please read till the end for maximum value.

What Is the Difference Between Ground Contact and Pressure Treated Lumber?

Pressure treated wood is softwood that has undergone chemical treatment to resist decay, rot, and termites. On the other hand, ground contact treated lumber is wood that possesses a high chemical retention level, and you can place it directly on or in the ground. Also, ground contact treated wood has better protection against decay and rot.

Pressure treated lumber is a common term among woodworkers as you can use it for simple home and DIY projects. But ground contact treated wood is quite rare as it is suitable for intense projects such as fencing and laying a building’s foundation.

In addition, most termites and decay fungi live in the ground. Also, moisture levels above the ground are higher than below the ground. Hence, you need wood with an appropriate protection level that will withstand these elements. And thus, ground contact wood becomes the perfect option.

As much as pressure treated wood can withstand harsh conditions, it can only take on so much. Fortunately, ground contact treated lumber factor in extreme high-decay and exposure applications such as horticulture sites and structural retaining walls.

On top of that, ground contact wood is perfect for building projects where you need dock or deck joists, ledger boards, and beams. Critical structures that determine the safety and integrity of the structure should always guarantee durability and strength. Also, structural parts that are difficult to replace will require you to use ground contact wood.

Will Pressure Treated Wood Rot In Soil?

Unfortunately, pressure treated wood will eventually rot in soil, especially if you use the wrong grade. Ground contact wood requires the most protection. Therefore, it will help tell the wood dealer the lumber’s end-use, so you’ll purchase the correct grade.

Even so, treated lumber will last longer than untreated wood. It has preservatives that keep the wood fibers strong for two decades or longer. Therefore, the lumber will serve you for some time while under the ground.

Also, where you position the wood and the preservative content levels will determine how fast it rots. So, please consider getting ground contact treated lumber for under-the-ground protection. The wood has additional protection that keeps it safe from aggressive decay organisms.

How Long Does Treated Timber Last in the Ground?

Treated timber can stay up to forty years without any decay or rot signs. But its longevity is compromised when you use it in the ground. So, you can only expect around ten years of usefulness for flooring and decking projects. Also, the type of wood, its uses, how well you maintain it, and the climate will extend or shorten the duration.

In addition, treated wood in the ground needs more protection as the moisture content and insect infestation underground is high. Thus, the wood will rot in a few years when you use untreated or low-grade lumber.

Luckily, you can get durable treated lumber by selecting the highest wood grade available. Also, it will help to insist on wood with a higher preservation chemicals content.

How Do You Keep Ground Contact Wood From Rotting?

Using the best preservatives is the best way to keep ground contact wood from rotting. Also, you should ensure that they follow the correct procedure if you are treating the wood at home.

The most effective preservatives prevent or slow down the decay rate or the wood’s biological infestation. More specifically, we have pentachlorophenol, creosote, and inorganic arsenic compounds like Chromated Copper Arsenate that offer superior lumber preservation.

Besides that, it is recommended to seal treated wood after sawing. You can use water-borne copper naphthenate as it is free from arsenic and chromium. Also, copper naphthenate protects the wood from rotting and lengthens its duration. Thus, appropriate for home and DIY projects.

So, would you like to make your wood resistant free? Below are some simple steps to follow when treating lumber or fence posts.

  • Dry the Wood

Store the wooden fence posts in a cool and dry space with enough ventilation to dry the lumber. In addition, remember that moisture content prevents the wood from taking up enough preservatives. Wet or green wood also encourages decay. Therefore, please wait for the lumber to dry well before use. The process may take months, but is the wait is worth it!

However, you can go ahead and treat the wood if it is already dry. You don’t have to wait any longer.

  • Determine the Most Suitable Preservative

It is necessary to select the preservative you want for your wood. You can choose either creosote, water-borne copper naphthenate, pressure-treated lumber, or pentachlorophenol. Also, please note that water-borne copper naphthenate is free from arsenic and chromium and thus safer to use.

  • Brush the Bottom Half of the Lumber With the Preservative

Dip your brush in the chosen preservative. Then, brush half or bottom third of the wood or fence post. Also, you can brush the whole wood structure if you want, but ensure that you treat the bottom part properly. The bottom part will be more vulnerable to wood rot than the upper area. Thus, it needs more fortification.

Besides that, you can apply the preservative by dipping the lumber upright in a bucket full of the wood preservative solution. However, the strategy is not effective if you have multiple wood or fence posts. Thus, you can just stick to brushing the lumber.

  • Allow Effective Absorption

Wait for about one hour after brushing the wood to allow the preservative to soak into the lumber. Then, apply a second layer and wait for another hour.

Next, continue brushing the lumber until it stops absorbing the preservative. This act signifies that the solution has soaked into the sapwood, including the heartwood. Therefore, the wood is rot and decay-resistant.

Finally, allow the lumber to dry properly and proceed to install the fence posts.

  • Brush Wood’s Top Part

Ensure that the fence posts are firm, and then brush the top parts with the preservative. In addition, concentrate on the fresh cuts to keep moisture from seeping into the fibers.

On top of that, assess the wood for damages and cracks. Then, brush the preservative and ensure it penetrates the lumber’s fibers. You can also apply as many coats as you want. But ensure that you give each layer enough time to dry.

  • Air-Dry

Let the fence posts, wooden posts, or rails dry for a few months before applying a sealant, paint, or stain. However, you can paint the lumber immediately if the wood was dry before treatment.

  • Apply Paint

You can paint the lumber using latex paint once the wood is dry. The formula is oil-based and prevents the lumber from weathering. Thus, it increases the wood’s durability and keeps it looking attractive.

What Is the Best Wood Preservative for Ground Contact?

The best wood preservative for ground contact is one that has copper naphthenate. It should also meet the American Wood Protection Association (AWPA) Standard. More specifically, you can use Copper-Green Brown and Tenino Copper Naphthenate wood preservatives. They have high copper naphthenate amounts, thus keeping the wood safe from fungi, decay, and insects.

On top of that, I recommend Tenino Copper Naphthenate over Copper brown wood preservative as it features a higher Copper Naphthenate percentage. Also, the main ingredient (Copper Naphthenate) comes from reclaimed and recycled copper products. Therefore, it offers the lumber more protection.

However, Tenino Copper Naphthenate is more expensive than its counterpart. Thus, it would be best to set aside enough money for the project.

Besides that, you can have the best preservative but use the wrong formula. This scenario will not yield a desirable outcome. Therefore, soak the part of the lumber that will have ground contact for about twenty minutes.

Lastly, apply a thick layer of the preservative and ensure that it soaks deep into the wood. Then, allow it to dry overnight before installation.

How Can You Tell If Wood Is Rated for Ground Contact?

SYP treated wood works best for above-the-ground projects. It is common for outdoor applications that are not subject to aggressive decay organisms in the ground. Therefore, it is recommended that you get wood rated for ground contact before installing the lumber underground. 

Normal treated wood undergoes enough treatment that enables it to withstand contact with low moisture levels. For example, watering systems and regular rainfall will not compromise the lumber’s longevity.

However, the wood will not handle intense moisture levels or pest invasion. Thus, it would be best to consider ground contact treated wood. So, how can you tell that the wood is rated for ground contact?

Look at the labels at the end of every wood piece. This way, you get to clarify the nature of the wood and how you can best use it. In addition, it is easy to identify wood treated according to AWPA standards. Look out for a label that says Ground Contact and the UC4A code. It will also have the Quality CheckMart symbol.

On top of that, ground contact lumber is more expensive than normal treated wood. It has additional chemicals that make it fit for underground projects. Also, you can decide to use a combination of both ground contact and ‘above the ground’ lumber depending on your project.

Lastly, remember that you can place Ground Contact lumber directly on or in the ground. Thus, please ensure that you check the board’s stamp for its chemical retention capacity. This label represents the minimum preservative amount the wood can retain.

Is Cedar Wood Good for Ground Contact?

Cedar has chemical properties that make it naturally weather-resistant and repels most bugs. It also has a lovely appearance, making it a common option for woodworkers. However, the lumber will not work well for projects involving concrete or direct contact with the ground. It will stay intact for a very short duration, then eventually deteriorate and rot.

Thankfully, you can use wood preservatives to increase cedar’s life span in the ground. These formulas ensure that the lumber does not collapse due to increased moisture content and insect infestation.

It would be best to care for the wood even if you use it above the ground. Fortunately, you can periodically refinish cedar and keep it from developing a fuzzy surface texture or cracking. The wood also accepts stains and sealers. Thus, maintenance routines are easy and affordable.

In addition, cedar is sensitive to UV light and darkens dramatically with intense exposure. Therefore, it is recommended to apply transparent sealers to preserve the lumber’s rich color and texture.

How Long Does Cedar Last in Contact With Ground?

Cedar prides itself on being durable. But, it can fail miserably in as few as five years unless you follow a few guidelines. Also, low-quality wood, poor drainage, and poor protection against insect damage contribute to cedar’s early failure.

Outdoor structures above the ground like gazebos, decks, fence boards, and pergolas last 30 years or longer. However, the lifespan reduces to 15 to 20 years if you use cedar for support or fence posts.

How Long Will a White Cedar Post Last in the Ground?

Generally, cedar posts will last eight to 27 years, depending on the wood type and existing weather conditions. Also, white cedar lasts longer than red cedar, which goes for about 20 years.

How Do You Keep Fence Posts From Rotting at the Ground Level?

First, you need the following supplies to get started: A wide paintbrush, digging bar, hand tamper, measuring tape, small paintbrush, level, post-hole diggers, reciprocating saw, exterior oil-based wood stain, exterior latex paint, ¼-minus gravel, and Water-borne copper naphthenate wood preservative.

After getting the correct supplies, follow the procedure below.

  • Store the fence posts in a cool and dry area. Also, ensure that there is enough air circulation to allow the wood to dry properly. Remember that moisture in lumber encourages rot and prevents the preservative from soaking into the wood fibers.
  • Use water-borne copper naphthenate and brush the bottom third or half of the post. In addition, ensure that you cover the entire post.
  • Wait for one hour and allow the preservative to soak into the fence posts. Then, apply an additional coat.
  • Continue adding coats of the copper naphthenate preservative until the lumber stops absorbing it. This scenario shows that the solution perfectly soaks the wood’s heartwood and sapwood. Then, allow the fence posts to dry before installing them.
  • Brush the posts’ top with the preservative after installation. Also, it will help to focus on where fresh cuts reveal or expose untreated wood.
  •  Wood cracks naturally gradually, which exposes the wood fibers to air and moisture. Thus, the posts could quickly rot. So, assess the lumber for cracks. Then, use the smaller brush to ensure that the copper naphthenate formula soaks deep into the wood’s cracks.
  • Allow the lumber to air dry for a few months before having a paint coat. This exercise ensures that the formula does not trap moisture inside the wood, causing it to rot from the inside out.
  • Also, you can paint the fence posts immediately if you had allowed the wood to air dry before applying the preservative. However, please confirm that the posts are dry to avoid any blunders.
  • Paint the dry posts, pickets, or rails with exterior oil-based stain or latex paint. This way, you protect the lumber from weathering and enhance its longevity.

That said, please remember that applying copper naphthenate wood preservative is necessary for fence posts, especially if you get them from fresh-cut wood. Hence, apply it liberally over the posts.

Also, ensure that you add a second application of the preservative even if you have pressure-treated lumber. The wood may resist rot and insects, but an additional preservation layer increases rot resistance abilities.

Untreated wood fences rot quickly because of prolonged moisture exposure in the soil. Also, the fences could fall, and you’ll have to replace them every few years. Thus, it will help to treat the wood to make it last longer. In addition, you can take extra steps to keep them from decaying or slowing down the rotting process.

For instance, Western Red Cedar is naturally rot-resistant and can last for decades if you treat it with a preservative. You can also install the wood to improve drainage, and it will remain intact.

Lastly, wear a breathing mask, gloves, and goggles while working with Copper Naphthenate preservative. Also, work in a well-ventilated space, preferably outdoors.

Frequently Asked Questions

Here are some of the questions that you are likely to come across regarding the topic:

  • How Good is Ground Contact Pressure Treated Lumber?

Generally, pressure treated wood has chemical compounds that resist termites, decay, and toy. However, they cannot withstand the moisture content and insect infestation underground.

Therefore, ground contact pressure treated wood becomes the best option. It features a higher chemical retention level and delivers superior protection against decay, rot, and insect damage. Thus, it allows you to use it directly on the ground or underneath.

  • Do Wooden Posts Rot in Concrete?

Setting fence posts in concrete without any preservation measures accelerate their rotting rate. Therefore, it is advisable to use pressure-treated posts as the rotting speed will be slow. In addition, ensure that you slope the concrete top away from the post to the grade level. This practice helps avoid water pooling around the wood’s base.

  • Can I Set Deck Posts in Concrete?

It would be best to place a deck post on the footing instead of inside the concrete as it may break. Concrete absorbs moisture while wood expands when wet. Thus, the wood will end up breaking the concrete and mess up your work,

  • Can I Treat Logs to Keep Them From Rotting?

Absolutely yes! You can treat logs to preserve them from rot or slowing down the rotting process. However, ensure that you dry the wood through natural air-drying or running a dehumidifier. Next, apply a wood preservative with borate or copper such as Woodlife Copper Coat, Copper-Green Brown, or Tenino Copper Naphthenate.

Also, please keep monitoring the wood as it is still at an increased risk of future decay and rot. Then, you can add additional coats whenever necessary.

  • Does Vinegar Stop Wood Rot?

Vinegar is among the fungicides you can use to defeat brown rot. Other formulas include hydrogen peroxide, boron solutions, propylene or ethylene glycol, hydrogen peroxide, tea tree oil, and baking soda.

In addition, vinegar provides an acidic environment ranging from Zero to 5.5pH that dries rot fungus.

However, you still need a preservative if you are using the wood pieces for underground applications. Therefore, please apply a suitable preservative with a high Copper Naphthenate percentage after drying the wood.


It is quite challenging to predict how long lumber can last in the ground. In addition, you’d have to consider aspects like wood type and environmental conditions before giving a good estimate. So, let’s engage with the subject:

How Long Does Ground Contact Wood Last?

Ground contact wood will last approximately eight years. But the duration will extend or shorten based on the preservative you use. Also, the kind and amount of pests in the region, the moisture content in the ground, and how temperature levels vary will determine the wood’s useful life.

Therefore, it is recommended to use a high-quality preservative and high-grade wood for the best results.

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Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.

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