How to Treat Wood for Ground Contact – Proper Wood Preservation

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It’s a bit weird that wood can begin to rot when it comes in contact with soil, considering that trees spend their whole lives (and their untimely deaths) stuck in the ground. Then again, trees have nutrients and roots that interact with the soil and allow them to rejuvenate and repair themselves over time. Wood is wood though, right? Well, yes, but woods need to be prepared for certain applications, especially when they’re going to be used outdoors. Let’s have a look at what causes wood to rot, the different types of rot you might come up against, and how to combat rot in all its incarnations. If you find yourself face to face with rot, there are loads of products out there to remedy your wood workpieces, and we’ll be having a look at those too.

Why Does Soil Contact Cause Wood to Rot?

While it might seem strange considering that lots of our homes and furnishings are made of wood, its natural disposition is to decompose over time once it’s been stripped or cut from its initial form as a tree. The question is then, what exactly causes wood to decompose once it’s been cut from a tree and fashioned into something else? Well, there are a number of factors that contribute towards wood slowly degrading including but not limited to microbes, density, exposure to moisture, insect infestation, and plant life taking up residence inside wood that has been planted into the ground.

It goes without saying then that wood that’s been fashioned into furniture doesn’t degrade because it’s not in contact with the ground in addition to being kept indoors and devoid of moisture. While wood is in contact with soil, it can come into contact with up to five million types of microbes, some of which tend to snack on or invest in the wood’s fibers which in turn causes it to degrade from the inside out. 

There are different types of rot too, brown rot which attacks the wood’s cellulose and causes it to break down into dry chunky bits. White rot has the same effect on the wood, although the characteristics of wood infected with white rot is that of a spongy, off-white texture.

Rot is relatively easy to defend against, but once it’s set in it can be nearly impossible to remedy, this is why it’s of utmost importance to protect your wood by preparing it properly before it’s placed into the ground.

Reasons for Prolonged Wood and Ground Contact

There are many instances where you would need to place wood in direct contact with the ground, each of which would need a specific treatment to prevent rot and general degradation. What are these applications though? Here are a few scenarios in which you would find yourself placing wood in direct contact with the ground and why they’re placed there.

Deck Posts

Deck posts are designed to elevate a deck above the ground and function as a sort of lookout platform for relaxation, barbequing, and even hot tubs! While most of us never think about these posts that support our decks, they are really important for the platform’s structural integrity and are in constant contact with the ground below. This means that they are at constant risk of rot and decay if they are not prepared and maintained throughout the course of the deck’s lifespan. 

Structural Posts

Structural posts serve the same purpose as deck posts, but they are often larger and the consequences of them failing are often much greater. Structural posts work to keep things like verandas, roofing, and non-load-bearing walls upright.

These are typically made of robust woods, which means that although they might be highly resistant to decay, they are by no means immune. These posts, in particular, should be monitored, maintained, and treated to combat the effects of insect infestation, rot, and general decay often.

Fence Pickets

Fence pickets are among some of the most commonly treated woods for ground contact and are what most of our minds jump to when thinking about wood that comes into direct contact with the ground.

This isn’t surprising considering how common picketed fences are in most towns (if you live in the big city, you’re forgiven), and since they’re often used to mark property boundaries far away from anything to protect them from the elements, they tend to need protection against external forces and ground rot. 

Sill Plates

Sill plates are often the first pieces of wood ever placed as a structural member of a house or similar structure in rural or suburban settings. What is a sill plate? It’s essentially a thick horizontal piece of wood used to join the rest of the house to the foundation. These wood pieces come into contact with soil and concrete, both of which tend to attract and house a variety of microorganisms that have a habit of chipping away at the wood.

Treating your sills with substances designed to defend wood against the ravages of ground contact is especially important in this context as it ensures that the foundation of your home (and everything inside it) is safe and sound.

Garden Boxes

While this might be one of the least thought of examples of ground contact wood, garden boxes have become quite popular in recent years. This is thanks to loads of people discovering the benefits of micro-farming and vegetable gardening in general, but many newcomers often overlook the importance of treating the wood used to construct their garden boxes for ground contact.

While this might not affect the flowers or vegetables inside the box, it can create an unsightly scene and become a general annoyance to discover that your beautiful garden box has rotted away thanks to those pesky microbes and/or insects. This is why treating the wood you use to create your garden box before assembling it is extremely important. If anything, this saves you some time and money later one, which is always a good thing.

What Are the Most Durable Wood Species for Ground Contact Applications?

We know that wood surfaces can be treated for ground contact applications, but are there any woods that are inherently better for applications where they would be in constant contact with the ground? The good news is that there are, and there are even woods that are treated for applications like ground contact before they reach the point of sale, so What is the best wood for ground contact? Let’s have a look at some of them and see just how good they are.

White Cedar

White cedar is a common sight around the eastern US, and its uses range from high-end furniture design all the way to ornate decorations and crafting. What makes white cedar the right choice for ground contact though? Well, first off, it’s really easy to work with because it’s quite soft and can be split quite easily, but its white cedar’s ability to resist rot and decay makes it an ideal candidate for ground contact applications.

Its heartwood in particular is highly resistant to decay and rot, with its sapwood showing marginal resistance although not quite as strong as the heartwood. Its light brown heartwood and off-white sapwood make it a great choice for outdoor applications where a rustic aesthetic is required. White cedar can also be pressure treated for increased resistance to decay if you need a wood that’s particularly robust.

Cypress Wood

Many veterans in the woodwork industry recommend using cypress as it is objectively the best wood for ground contact above any other wood species. Online forums and social media discussions further reinforce this notion with even DIY weekend warriors praising this wood for its hard-wearing nature and innate ability to resist rot and decay. 

Cypress wood has been used for years as an easy and effective means to solve engineering and construction problems that would otherwise require synthetic materials, a few examples of this are burial caskets, bridges, boats, and even railroad ties. This wood is virtually watertight because of its tightly packed grain, which is why it makes such a good construction and crafting material for demanding applications.

On the off chance that a microbe or fungus does manage to worm its way into a cypress, it rarely affects the structural integrity of the wood. Instead, the result a unique appearance, known as burl grain, which is actually quite sought after in some crafting communities.

Redwood

Redwood is one of the oldest woods on the face of the planet, with some examples of the species living up to 100 years. It should come as no surprise then that it is one of the most resilient wood species on the face of the planet, being able to withstand conditions that would make most other wood types crumble under the same conditions. Redwood, then, is one of the best woods to use when looking for some board to use for ground contact, rivaling even pressure-treated wood in its ground contact effectiveness.

But what makes redwood so good at resisting decay and rot? Well, the key is in its heartwood (the core of the tree) which contains a bunch of little particles called extractives, these are what help protect the wood against rot and decay throughout its lifetime as part of a redwood tree and remain there once it’s been cut into the wood board. If you’re looking for a wood that can get by without being pressure treated, or simply can’t get your hands on some pressure-treated wood, redwood is a great alternative.

Pressure-Treated Wood

The term pressure-treated wood gets thrown around a lot, but what does it actually mean? Pressure-treated wood is any wood species that has been treated with a range of chemicals and then placed into a pressurized chamber in order to bond these chemicals with the wood’s fibers. Pressure-treated wood is highly resistant to rot, mold, insect infestation, moisture damage, abrasion, and general decay.

If you happen to have the right equipment and some time on your hands, you could have a go at pressure-treating wood yourself, although we strongly recommend only using the methods and/ or buying pressure-treated wood that meets the standards of the international code commission (ICC) or American Wood Protection Organization (AWPA). 

If you’re wondering how to identify pressure-treated wood that has been graded for applications that require ground contact, look for the UC4B or UC4A marking on the pressure-treated board.

Pressure-treated wood does a fairly good job of protecting workpieces against rot and general decay, although it’s always best to use a wood preservative in addition to pressure treatment to ensure that your wood stands the best chance of surviving being submerged into the soil.

How to Stop Wood from Rotting in the Ground

While the best way to prevent wood from rotting in the ground is to use a protective coating on it, there are other ways of ensuring that your wooden workpiece like fence posts and flower boxes are protected against the ravages of degradation. What are they though? Well, we’ve prepared a few methods you can use besides protective coatings to prevent the wood from rotting in the ground.

Using Concrete

A great way to prevent rot and decay in ground contact wooden workpieces is to use concrete to secure them. This not only ensures that your posts and other ground contact wood applications will be protected from rot and decay but ensures that your workpieces will remain sturdy for years to come.

If you’re wondering how to treat wood for ground contact using concrete, the trick is to use quick setting concrete, which unlike conventional concrete sets in roughly 30 minutes depending on ambient conditions. Simply dig a hole to accommodate the size of your workpiece and inset it, then pour some of the dry quick-set concrete around your workpiece and add water to the mixture. After roughly four hours the workpiece should be ready to bear weight and is now protected from rot and decay!

Using Wood Treatments

Wondering how to treat wood for ground contact using wood treatments? There are loads of wood treatment products on the market that allow you to prepare your wood for ground contact before they’re inserted into the ground. These products are often a chemical treatment that seeps into the grain of your wooden workpiece and binds with them to ensure that your workpiece is highly resistant to rot and decay.

If you’re going to be using wood treatment products for the first time, ensure that you do so outdoors and while wearing the appropriate personal protective gear like gloves and a face mask.

This method is one of the less labor-intensive ways of protecting any wood board that you know will be in constant contact with the ground, and what’s more, is that everything you’ll need is readily available both in-store and online.

Using Paint

Treating lumber for ground contact using paint is more of a temporary solution to what is very much a long-term problem. Why? Well, there is an important distinction between wood treatments (such as wood stain and pressure treatment) and surface coatings (paints epoxy resin) and in most cases surface coatings typically don’t stand up to the test of time quite as well as wood treatments. 

This is because wood treatments penetrate beneath the surface of the board and bond with the wood fibers, protecting them both inside and out. Surface coatings tend to degrade over time which means you’ll find yourself maintaining and/or replacing them much more often than you would wood treatments.

Keep in mind that treating lumber for ground contact using things like oil-based paints is only effective in the short term. Your intention should be to eventually use substances graded for more long-term protection. However, this is considerably more effort and involves uprooting your workpiece again.

How to Treat Untreated Wood for Ground Contact

Knowing the best product for preserving your wood for ground contact applications is pretty useless without knowing how to apply your preservative. This is why we have taken it upon ourselves to provide you with a short tutorial detailing how to treat untreated wood for ground contact, or simply for applications where they might need some help against forces that might cause them damage and/or decay.

Prepare Your Workspace

Since most wood treatments have a pretty strong smell we highly recommend working outdoors, or if not possible, to ensure that your workspace is well ventilated, Next, ensure that you cover the floor of your workspace or you’re paving with some tarp or old newspaper to ensure that they don’t get permanently stained. 

Always ensure that if you intend to use any type of wood preservative that you have the appropriate personal protective gear including a face mask and gloves graded for use with wood treatment products.

Prepare Your Workpiece

Although this might seem a bit counterproductive considering that your workpiece is going to be placed into the ground, you should give it a good cleaning before you get started. Some soapy water should do the trick, just give the bit you’re about to treat a good once over and allow it to dry off completely. 

Once it’s all dried out you should give your workpiece a light sanding. For smaller workpieces feel free to use some sanding paper, but you might want to consider using a power sander for larger or more awkwardly shaped workpieces. Once your workpiece has been sanded to your liking, use a clean, dry cloth to remove any stray wood particles before moving on to the next step in the process.

Apply Your Wood Treatment

Now, for the moment you’ve been waiting for: applying your wood treatment! There are two ways you could go about this; you could pour your wood treatment into a container and apply it to your workpiece using a brush and/or roller.  Or, you could simply pour your wood treatments into a larger container and submerge the wood pieces into it. Either way, you’ll be getting the job done, but if you have a large number of workpieces, we recommend the second option in the interest of saving some time and effort.

For the first method, pour the amount of wood treatment you’ll need into a container and give it a good mixing with a stick, this ensures that any of the additives that might have sunk to the bottom of the mixture over time are mixed evenly with the rest of the substance. 

Next, insert your brush and apply your wood treatment to the board following the direction of the grain. If you intend on applying multiple coats, we recommend waiting for the manufacturer’s recommended time period for each coat to dry before moving on to the next.

If using the submersion method, simply place your wood into the wood treatment formula for roughly 30 minutes, then remove it and allow it to dry overnight before installing it into your desired spot in the ground.

Preventing Rot

As we have emphasized: it is very important to stop rot before it sets in. If you don’t, the results can be very costly. Take the time to do the proper preparations, and use the right materials in the recommended way in the proper setting. Knowing how and why wood deteriorates is your best weapon against unnecessary effort and expense down the road.

Now that you know what causes wood to rot, which scenarios would require the use of a wood treatment to protect wood against long-term ground contact, what methods you can use to protect your wood from corrosion, and how to use wood protection treatments, it’s time for you to get out there and put your new-found knowledge to the test. Remember to always work in a well-ventilated area and always wear the appropriate personal protective gear!

Frequently Asked Questions

What Is the Best Pressure-Treated Wood for Ground Contact?

If you’re looking for the best pressure-treated wood for ground contact, you should do your best to look for those with the marking UC4B or UC4A. Why? Boards that have been marked with these indicators have been graded for use below ground and are highly resistant to rot and decay.

What Lumber Is Required for Ground or Concrete Contact?

While there are many wood species that are naturally resistant to all of the challenges that ground contact comes with, such as redwood and cypress, pressure-treated wood is by far the best for this application. Pressure-treated wood is essentially infused with chemicals that preserve the wood and prevent mold and microbes from eating away at your workpiece.

How Long Can Ground Contact Wood Last?

While all of us would like our fences and garden boxes to last a lifetime, unfortunately, most woods that come into constant contact with soil only last for about 10 years. The lifespan and protection of your wood can be extended by treating your wood before inserting it into the ground.