Applying
Oil Finishes
To Hardwoods
The gentle art of applying an oil finish is a study in technique. Numerous articles on the topic attempt to codify rules that, if followed, should result in a clear, glass-like finish. My experience has been that getting those kinds of results takes more than following a recipe. A carefully trained eye and and heap of patience are necessary requirements.
Furthermore, an oil finish is what we like to call an organic finish. Lacquers and urethanes leave a coating over the wood. Oils dry in the wood. Consequently, when you touch a lacquered or urethaned piece, you touch a synthetic coating. When you touch an oiled piece, you touch wood.
If you've never done an oil finish, I suggest first that you simply finish the flat face of a small board. A foot or so of 1x6 will suffice.
You'll need the following:
- Sandpaper from 80 grit to 1500 grit, plus microfiber paper if you want to go the extra mile.
- A sanding block for flat surfaces.
- Oil: Danish furniture oil is easy to work with. Linseed and tung oils will do quite well also. Ultimately, this will be a matter of taste.
- T-shirt material to apply the oil.
Begin with the coarsest grit and sand, as always, with the grain. You will want to make sure that all of the scratches from the milling process, or whatever else, are gone. This raises the first point:
You have to learn to distinguish between scratches from the sandpaper and scratches from other sources.
This takes practice. You'll find out if you identified the scratches correctly when you get to the next grit. If the scratches disappear with the next grit, then you chose wisely. Otherwise, return to the coarser grit until only sanding scratches remain.
You have to look very closely at the wood. I like to hold the wood at a slight angle, about 12 inches from my eye under incandescent light. You'll get to know what the fibers of the wood should look like (this varies with species and there is no substitute for experience here). If you have trouble seeing the scratches, you can wipe some mineral spirits on the surface and the scratches will pop out. If you're not using waterproof paper, be sure to only resume sanding after the mineral spirits have evaporated.
About grades of sandpaper: I use whatever is most readily available, but I err on the side of waterproof, auto-body grade paper for the higher grits. Also, I spare no expense on paper. You'll develop a feel for the grits and you'll know when the paper isn't cutting like it should. At first sign of this, get a new piece. You'll thank yourself that you did.
Work through the coarsest grit very carefully. The later grits will go much faster if you do. I usually spend about three times as long with my first grit than with any of the others. It makes the final grits much more rewarding! As always, brush off the piece after each grit as the dust will be coarser than the next grit. I prefer to brush and run my hand across the piece to using tack cloth. I do this because the natural oils in my hand will pick up dust, and I get to feel the progress. Start with a clean hand.
After 1500, apply a thin coat of oil with the t-shirt material. Often, sources will suggest bathing the piece in oil. I prefer to let the piece soak the oil in slowly, in thin coats. Wait 5 or 10 minutes and rub off the residue. Often I'll sand with 1500 at this point, just to stimulate the surface.
I have read many sources and talked to many woodworkers who suggest that oil will not soak into wood sanded this smooth. I have never had a problem with oil soaking in. I prefer to oil later because I have greater control over how much oil gets into the wood — this is the case because coarser wood has more surface area (a bumpy surface has more surface area than a smooth surface), and so absorbs a greater quantity of oil. I think that this is why many think that oil is not absorbed into smooth wood. Plus, if you oil early, the oil can gum up your paper — you'll end up sanding oily bumps rather than plain wood.
I'll usually let a piece sit overnight after a few thin coats. The next day, I'll apply another coat. By this point, the wood will be rather saturated. Your task will be to get the reside off of the surface. I do this with 1500 paper. The paper will clog quickly, so you'll have to use a lot. But the results are worth it — at just that saturation point, the wood will feel like glass.
If you so choose, continue sanding with microfiber paper. On sculpted pieces I'll go up to 12000. The finish is amazing.
Further Tips
If your piece has lots of curves, you'll have to spend a lot more time sanding. Very little can substitute for the fingers as far as guiding the paper across a curve goes. But for those really tight angles that are smaller than the radius of your smallest finger, I like to wrap a small piece of sandpaper around a dowel or screwdriver. Then I work the piece like I'm using a fine file.
End grain is difficult to get smooth. If you have a very sharp hand planer, you might want to use that to take out saw marks. Otherwise, keep your sanding block at 90 degrees to the surface and just lay into it! It takes a lot of effort, especially with very hard woods like bird's eye maple. Again, you'll want to develop an eye for how scratches look in endgrain of your chosen species.
If the piece is already assembled, it can be really hard to get the oil into corners, for example if you're refinishing a shelf or desk. In these cases, I will sometimes pour and spread the oil with the rag, rather than oiling the rag then spreading with that little bit. Also, sometimes I'll saturate the rag and press it into the corners.
If you will be assembling the piece, be sure to sand what will be the hard-to-reach surfaces before assembly. You will not be able to get the finish you want in, say, a corner unless you finish the pieces prior to assembly.
If you have questions or suggestions, please feel free to contact us. Happy Finishing!