A well installed wooden fence should last for years. And fences made with the right type of timber, (such as White Oak), can last for decades.
However, Oak fencing will only last if it has been given a particular kind of chemical treatment. These chemicals not only safeguard your fence from the rain above, but also protect it from the damp underneath as well.
So in this post, you will learn why not all types of Oak are suitable for your fence. You will also learn why this durable hardwood needs to be pressure treated, if it is to last outside.
And we reveal the special kind of ‘ground contact’ pressure treatment that’s crucial for your Oak wood fences longevity. Let’s dive right into it…
This post may contain affiliate links to products that we receive a commission for (at no additional cost to you). Learn more here.
Are Oak Wood Fence Posts Any Good?
It depends on the kind of Oak. Typically, Oak fencing is made from White Oak, which is a naturally weatherproof wood.
It’s used for making a range of outdoor structures, from decking to garden furniture. And it’s water-resistant qualities sets it apart from its Red Oak cousin.
You see, Red Oak and White Oak both have open-pored wood grain. However, what makes White Oak special are its unusual Tyloses.
Tyloses are cell outgrowths that cover up and seal White Oaks pores. This prevents water from seeping into this timber, protecting White Oak from water damage, rot and decay.
So, White Oak wood fence posts are fairly durable when used outside. However, this wood still needs extra treatment to protect it from the very worst of rainy weather.
Just How Long Will An Oak Post Last In The Ground?
Without any treatment or sealant, unfinished White Oak wood will last about two decades. Although, those fence posts won’t be completely upright for much of that time.
In other words, if you want Oak fence posts to really stay firmly in place, they need to be chemically treated.
Why? Do Oak Posts Rot?
Yes, they do, especially if they have direct contact with ground soil.
All of the moisture in soil will seep into Oak wood, causing even this rot-resistant lumber to decay. Particularly in very humid and/or otherwise damp environments.
So What Can You Put On Oak Fence Posts To Stop Them From Rotting?
If you are working with untreated Oak wood, then you need to coat it from head to toe in a urethane sealant.
Urethane is the key water-resistant ingredient found in polyurethane finishes. But, a typical polyurethane finish isn’t going to be waterproof enough for the great outdoors.
You need a Urethane finishing coat that can handle very damp conditions. Which is why using Spar Urethane, (also known as Spar Varnish), is your best bet at sealing an untreated Oak fence post.
Spar Urethane is a waterproofing finish widely used to seal marine side decking and boats. And if Spar Urethane can protect boats from the sea, then it can protect Oak from the elements.
However, sealing a fence post only applies if you are working with untreated Oak. And, nowadays, if you purchase your Oak fencing from the lumber yard, it’ll likely have already come chemically treated.
This is called ‘pressure treatment‘. And it involves infusing wood with wood preservatives designed to make wood more water-resistant and rot-resistant.
Do You Need To Treat Pressure Treated Oak Posts?
You can if you want to. However, there is no need to add extra sealants (or other treatments) to an Oak fence post that has been pressure treated.
But, that’s only if the fence post has been stamped as ‘Ground Contact Rated Material‘.
Ground contact rated timber has been pressure treated. But, what makes this pressure treated wood special, is that it’s been treated with chemicals that meet the AWPA’s (American Wood Protection Association) UC4 standard for wood preservation.
These UC4 standard preservatives are designed to protect wood from the rot that occurs with permanent contact with ground soil. So, provided your Oak wood fence posts are Ground Contact Rated, you won’t need to coat it in a sealant.
To Wrap Up, Here Are The 3 Key Takeaways…
1). White Oak wood is naturally water-resistant. It is suitable for exterior structures, as it is a durable and rot-resistant lumber.
2). However, bare White Oak wood is not completely weatherproof. So it will need to be chemically treated and/or sealed to protect it outside.
3). If you use Ground Contact Rated pressure treated Oak wood for your fence posts, you don’t need to treat or seal those posts.
Specifying with AWPA Use Categories for Construction | Preserve SPEC