There’s so much contradictory advice when it comes to Teak oil. And while this finish comes highly recommended for exterior wood, it isn’t an optimal finish for outdoor use.
You see, Teak oil works best on durable woods that don’t need much (if any) waterproofing. Let’s take for example, Teak wood (which is the precise type of wood Teak oil was originally created for).
Teak wood is a hardwood that’s naturally saturated with its own wood preserving oil. This timber is so oily, it can be difficult to get it to soak up a penetrating oil finish.
Unfinished Teak wood furniture can last for decades without rotting away. And the real reason we coat it with Teak oil is to help preserve Teak woods color. That is because, without the UV inhibitors inside Teak oil, direct sunlight will turn Teak wood gray.
But, Teak oil isn’t completely waterproof, isn’t very durable, and it needs regular reapplication. In fact, it isn’t even all that scratch-proof either.
So, when it comes to exterior Douglas fir structures, can Teak oil really protect this softwood?
Well, in this post, you will learn what actually goes into Teak oil—and why no two Teak oil products are ever the same. You will also learn exactly why Douglas fir (in particular) needs more than just Teak oil to protect it.
And we reveal the best oil-based finish you can use to preserve that Douglas fir wood furniture piece.
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What Is Teak Oil Exactly?
Teak oil is a blended oil that contains a lot of different ingredients. This finish mixes natural oils, (such as Linseed oil and Tung oil), with mineral spirits, varnish and UV inhibitors.
This finish was originally designed for Teak wood (hence its name). Yet, despite its name, it does not contain any natural oil from the Teak tree.
And, because this blended product is not a natural oil, no two Teak oil brands contain the same balance of ingredients.
And Can You Use Teak Oil On Douglas Fir Wood?
Teak oil can be used on Douglas fir like a wood preservative. It will sink into this softwood, and safeguard it by making this lumber less water absorbent.
Also, the UV inhibitors contained in most Teak oil finishes will protect Douglas fir from UV-damage. However, despite all of this, Teak oil is not the best finish for Douglas fir.
Does That Mean That You Can’t Oil Douglas Fir At All?
You absolutely can apply an oil finish onto Douglas fir. However, penetrating oil finishes like Teak oil aren’t waterproof.
And that is a problem when it comes to Douglas fir, because this softwood lumber is frequently used for outdoor structures such as decking and garden furniture sets. Basically, a Teak oil finish isn’t going to be enough to protect this lumber from the elements.
What’s more, Douglas fir isn’t a very dense wood, and is in fact a fairly soft timber.
According to the Janka hardness scale, (which measures just how dent-proof a piece of wood is), Douglas fir is softer than other types of choice outdoor lumber.
Douglas fir has a Janka rating of 660 lbf. And that means that it takes 660 pounds of force to make a dent in this timber. While Teak wood, (widely used for outdoor structures and decking), has a Janka rating of 1155 lbf.
And Babul Acacia wood, (an increasingly sought-after wood type for garden sets), has a Janka rating of up to 2300 lbf.
Related Post: Can You Apply Teak Oil On Acacia Wood?
What this all means is that Douglas fir is going to need a finish that will protect it from scratches and dents too. And this is something that those thin coats of Teak oil will fail to do.
So, Is Douglas Fir Really A Good Outdoor Wood?
It is…but not because of it’s density. It’s outdoor advantage comes in the form of its stability.
Wood is a very, very water-absorbent material. As it absorbs water, wood will expand. And as the water dries out and evaporates, wood shrinks.
This wood movement can be a problem in extreme cases, because it can end up warping wood, twisting straight boards out of shape.
Related Post: Is Whitewood Really Any Good For Framing?
However Douglas Fir Boards Experience Minimal Warping
Douglas fir, on the other hand, is a weather-resistant lumber. And this is because it barely expands and contracts…even when its been drenched with (rain)water.
In short, once Douglas fir wood has finished seasoning, moisture and humidity won’t be able to warp the boards of this lumber.
Related Post: How To Season Wood (7 Tips)
OK Then, Why Bother Seal Douglas Fir At All?
Well, water won’t destabilize Douglas fir. But, water can cause rot and decay to set in and eat away at it.
Sealing this lumber is more about preventing rot from setting in. It also prevents bugs and termites from burrowing into the wood too.
Without a waterproofing sealer, untreated Douglas fir outdoor furniture will rot away within 3-6 years.
Does Teak Oil Make Douglas Fir Wood Waterproof?
Teak oil is a penetrating oil that gets absorbed into wood grain. However, it leaves very little durable build up on the surface. And what little resin it does leave behind can be water damaged.
So no, Teak oil won’t waterproof Douglas fir, because Teak oil isn’t a waterproofing sealer. It is more of a wood preservative, making lumber more water-resistant.
So How Do You Treat And Seal Douglas Fir Wood?
Douglas fir needs a sealing coat that will offer both the UV protection of a Teak oil, with the waterproofing of a polyurethane finish.
Which is why Spar Urethane, (also interchangeably referred to as Spar Varnish), is the best finish when it comes to sealing exterior Douglas fir.
Spar urethane is a type of varnish that contains urethane (the same stuff found inside polyurethane sealers). This clear coating finish can be used for both interior and exterior wood. And it contains UV blockers that will minimize the effects of color fading.
And one of the best Spar Urethane products on the market is Rust-Oleum’s Oil-Based Ultimate Spar Urethane.
It comes in a Gloss, Semi-Gloss, and Satin finish. And it is a weatherproofing finish that prevents rain and moisture from soaking into wood.
This oil-based sealer is scratch proof, so it will even prevent scuff marks from marring your garden set.
To Sum Up, Here Are The 3 Key Takeaways…
- 1). Douglas fir is a stable wood. However, it still needs a waterproofing sealer if it is to be used on outdoor structures.
- 2). Teak oil is water-resistant, but it is not a wholly waterproof or scratch-proof finish.
- 3). Use Spar urethane to seal Douglas fir. Spar urethane will waterproof wood, safeguarding it from decay, scratches, and UV-rays.