If you are planning on building something outdoors made out of wood, then using the right species is extremely important.
The point here is that not all types of wood are resistant to water. Some types of wood are nearly waterproof, some are water-resistant, and some will start absorbing moisture the second they come into contact with water. Today, we want to take a closer look at oak.
So, how waterproof is oak? Is oak a suitable type of wood to use outdoors?
Is Oak Naturally Waterproof?
One of the big advantages that you get with oak wood is that it is naturally quite water-resistant, although not 100% waterproof. With that being said, in terms of overall water resistance, this wood is nearly as good as it gets as far as hardwood is concerned. After all, there is no single type of wood out there that is actually 100% waterproof.
However, as far as the different types of hardwood and softwood go, oak is known for being quite resistant to the elements, especially moisture and pests.
This wood has a fairly tight and straight grain, combined with a relatively dense and hard structure. This combination of a tight grain with a dense and hard outer surface means that moisture has a very hard time getting past the outer layer, which is also true for pests, mold, and fungus. Do keep in mind that white oak tends to be a bit more water-resistant than red oak.
Does Oak Absorb Moisture?
This wood is also known for being ideal for outdoor use because it doesn’t really absorb much moisture. Going back to the previous point, oak has a fairly tight grain structure. At the same time, this wood is also quite hard and dense, and also has very small pores.
All four of these factors come together to ensure that oak does not absorb much moisture. At the same time, this material does also contain a few natural oils and resins, which are naturally water-repellent. Therefore, oak does not easily absorb moisture and is therefore ideal for outdoor use.
Of course, this resistance to water absorption only goes so far. If this wood is constantly submerged in water for a prolonged period of time, chances are that it will begin to absorb moisture, especially if it has not been sealed properly. Something that does need to be said is that white oak is much more moisture-resistant than red oak.
Does Oak Rot When Wet?
Although white oak is more resistant to rotting when it is wet than red oak, both types are quite resistant to this process. The fact is that both types of oak don’t easily absorb water, which means that rotting doesn’t readily occur. With that being said, if these types of wood do absorb water, they may begin to rot over time, although this will take a while.
What you need to know is that all types of wood will eventually start to rot if they are wet, but some may start to rot within just a couple of weeks, whereas others may take years. Oak is one of these types of wood that is going to take many months, if not years, to start to rot if it gets wet.
However, keep in mind that if wood such as oak is 100% submerged in water, it cannot begin to rot. In the grand scheme of things, although oak will eventually start to rot when wet, just like other types of wood, it is going to take a very long time and constant exposure to high levels of moisture.
Does Oak Warp When Wet?
Something that does stand out about oak is that even when it gets wet, it is not very prone to warping or cracking. This is one of the more stable types of wood on this front. If it does get wet, it should be able to dry out without warping, cracking, bending, or changing shape in any way.
How to Waterproof Oak Wood
Waterproofing oak is really no different than waterproofing any other type of wood, and there are a few different options that you have at your disposal. You can choose to put lacquer on the oak, varnish, polyurethane sealant, paint, or even an oil finish.
If you want to make your wood look really warm and dark, and you want to protect it from water, using tung oil is recommended. However, the issue with this kind of oil is that it does require constant reapplication on a yearly basis, as it will start to wear off.
Our personal recommendation here is that you go with a polyurethane sealant. Polyurethane sealants, especially oil-based polyurethane sealants, are extremely durable and long-lasting.
They are 100% waterproof, so they’re never going to let any water in, and they also don’t need to be reapplied very often. At the same time, these sealants also come in many different finishes, so you can choose what the final appearance of your oak is going to be.
As you can see, oak is a perfectly fine option to use for outdoor purposes, even if you don’t use a sealant or waterproofing agent. With that being said, if you do want your outdoor oak furniture or buildings to last for as long as possible, especially in terms of moisture resistance, then we do recommend sealing it, especially with an oil-based polyurethane sealant.