This advice applies to penetrating oils such as mineral oils, linseed oil, tung oil, and Danish oils like Tried & True, as well as any of the hard wax oil finishing products.
Before we get into applying multiple coats of oil, and before the first coat even goes on. It’s important to prep the surface of the wood to get the best results.
How do I prep the wood before the first coat?
Sand through the grits like you normally would, and be sure not to skip any. I usually start at 100 grit for most projects and sand up to 180 or 220, depending on the level of polish and smoothness I’m going for.
Then, even though we’re applying an oil-based product that won’t raise the grain the way a water-based product would, I still wet the wood to raise the grain, then lightly sand it with my final grit to smooth the raised grain back down.
Why raise the grain if I’m using an oil finish?
Even though you’re applying a finish to the wood, oil-based products like Danish oil don’t build a coat of finish the way lacquers and polyurethanes do. Those are film finishes; they encapsulate the wood in a layer of finish. Danish oil is a penetrating finish. It soaks into the wood and conditions it, which means water can still interact with the wood fibers after the fact.
When freshly sanded wood gets wet for the first time, it causes those fibers to swell and the surface to go rough. So it’s a good idea to pre-raise the grain before you ever apply oil, rather than dealing with it after.
How thick should each coat be?
Most hand-rubbed oil finish manufacturers instruct you to apply it in very thin coats. This lets the surface dry faster and keeps the oil you’re applying from displacing the natural oils and waxes already present in the wood.
That said, applying a hand-rubbed oil finish in truly thin coats is labor-intensive and takes a lot of elbow grease. So for most woods, especially domestics, I usually apply it fairly liberally and then wipe the excess off so the surface can dry faster.
I do caution against liberal application on naturally oily woods, like purpleheart. Many exotic hardwoods carry a lot of natural oils and waxes. If you apply too much oil over these species, it can displace those natural oils and waxes, causing them to collect on the surface and leave you with an undesirable finish. So for oily and waxy woods, I recommend sticking with the elbow grease and applying the finish in as thin a coat as possible.
So, how do I prep between coats?
First, wipe off any excess finish from the previous coat, then let it air dry for a full day. Since this isn’t a film finish, sanding between coats isn’t necessary unless you feel or see a rough spot that got missed. If you want to add a little more luster, buff the surface with #0000 steel wool before applying the next coat.
That’s really it. The most important part of applying an oil finish is the prep before the first coat goes on. After that, the minimum prep between coats is just wiping off any excess and letting it dry a full day before the next one.
How many coats do I need?
I usually apply at least three coats, but the right number comes down to the look and feel you’re going for on that particular project.
Safety note: Many oil-based finishes generate heat as they cure and can spontaneously combust, starting a fire. Always lay oily rags flat to dry before disposing of them; a pile of oily rags is a common cause of shop fires.
I’m the owner of Benham Design Concepts, a mixed media art studio where I design and build custom furniture and other works of art using wood, glass, stone, and various metals.
In this blog, I talk about the art I create, my journey, and the things I learn along the way.