Like most materials, wood will start to rot and decay once it is exposed to the elements but luckily for us, we can treat the wood to protect it from rain and the sun to make it last a whole lot longer than it usually would.
Protecting wood against the elements is not hard to do at all. In fact, there are a lot of different ways to prepare wood for outdoor use but when it comes to preparing wood for ground contact, then we will have a lot more to watch out for and protecting wood properly from rotting in the ground is a whole lot more complicated.
But don´t worry!
I tried a lot of different ways to treat wood for ground contact and in this article, I will show you the very best methods to protect your wood from rot and decay when it is partially or fully underground.
The best way to treat wood for ground contact is soaking the part of the wood that will have contact with the ground in wood preservative for 20 minutes. Then paint the part of the wood with a thick layer of the same wood preservative. Let the wood dry overnight before you put it in the ground.
This is probably the most commonly used and one of the best methods for preserving wood.
You should use a wood preservative that contains copper naphthenate and it should meet the AWPA (American Wood Protection Association) Standard for preserving wood for ground contact.
I personally had excellent results with Tenino Copper Naphthenate wood preservative. You can find it here on Amazon.
I usually use a bucket to soak the wood with the wood preservative but you can also use a pressure sprayer to soak your wood.
You need to thoroughly soak the part of the wood that will be in contact with the earth with the wood preservative.
So either fill a bucket with enough wood preservative to cover the necessary parts of the wood or use the sprayer to spray the parts of the wood with the preservative.
It doesn´t matter what method you use just make sure that the wood is completely soaked with the preservative for at least 15 minutes.
Then use a paintbrush to apply a thick coat of the preservative to the part of the wood that will be in contact with the ground.
Let everything dry overnight before bringing the wood into contact with the ground.
Your wood will now be perfectly prepared for ground contact but always remember, there really is no permanent way to protect the wood from rot and decay so no matter how well you applied the preservative your wood will eventually rot.
But now that you properly protected it from moisture through the preservative it will take years until it starts to rot.
Choosing the Right Kind of Wood for Ground Contact
You can obviously use any type of wood, prepare it for ground contact, and you will be fine for at least a year but by choosing the right kind of wood you can easily quadruple the live expectancy of your project.
So if you want to create something that lasts then you should start by choosing the right type of wood for your project especially if it has contact or if it is even partially buried in the ground.
First off I would highly recommend using pressure-treated wood if you plan on having it contact the ground.
Make sure to only use pressure-treated wood that has been treated by the standards of the ICC (Internationa Code Commission) or the AWPA (the American Wood Protection Association).
Use either UC 4A or UC 4B treated lumber. These labels indicate that the wood is intended for below-ground use.
Even though this lumber is declared as below-ground use you still have to prepare it for the contact with the ground by using the wood preservative as described above. Especially if you cut the wood before using it!
There are a couple of wood types that are especially good for underground use. Depending on where you live a different type of wood can be the right choice for you.
If you live in a swampy or very wet environment then white cedar is probably one of the best choices for you.
Cedar is naturally resistant to fungi of all types and it is also naturally resistant to rot.
Just remember to get pressure treated white cedar that is either labeled UC 4A or 4B!
Cypress wood is the best choice for underground use.
Its natural resistance against moisture makes it perfect for below-ground use.
If you are not sure what kind of wood to choose then chose cypress wood. You can´t go wrong with this one!
Best Ground Contact Wood Preservatives
And here is why!
Both of these have high amounts of Copper Naphthenate in them.
Copper Naphthenate is one of the main ingredients of wood preservatives and it is responsible for protecting the wood from decay, fungi, and insects.
A high amount of Copper Naphthenate is, among other things, a good indicator of how well a wood preservative is going to be able to preserve the wood.
I prefer Tenino over Copper Brown Wood Preservative because it has a higher percentage of Copper Naphthenate in it, it meets the AWPA-Standards, and the main ingredient (Copper Naphthenate) is sourced from recycled and reclaimed copper products.
I personally worked with both of these products and they worked really well for me. I tried a couple of other products but I can´t really recommend those.
But if I find another wood Preservative that does work well and that is maybe even a bit cheaper then I will update this article right away!
How Long Does Ground Contact Wood Last?
This is probably the one question that you had from the start of this article. Unfortunately, it is not easy to give a straight answer here.
How long a pressure-treated and with wood preservative-treated piece of wood lasts in the ground depends on a lot of different factors like the amount of moisture in the ground, the kind and amount of insects in the area, how high the temperature changes are, and so on.
Generally, ground-contact wood lasts for about 8 to 12 years depending on the location of the wood, the type of the wood, and how well it was preserved before burying it. If the ground is very moist or if the surrounding temperature changes frequently then the wood will generally not last as long.
While it is literally impossible to predict how long wood will last in the ground it is generally a good estimate to say that every properly treated piece of wood can at least live for 8 years.
But most posts can survive for way longer than that especially if they were cast in concrete.