10.2: Oil Finishes
- Page ID
- 67213
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Oil finishes are useful when you want the wood to remain visually and physically close to its natural character. There are many other types of finishes, and your are encouraged to check those out by enrolling in a finishing class we offer.
All finishes can deepen the color of the wood, emphasize grain and figure, and create a surface that is pleasant to touch.
In WMT 101, you will encounter two basic applications:
- a food-safe oil for the cutting board; and
- an instructor-supplied furniture oil finish, such as an Osmo product or similar finish, for projects such as the tool tote.
Always use the finish supplied or approved by your instructor.
Learning Outcomes
After completing this section, you should be able to:
- Explain how an oil finish changes the appearance of wood.
- Distinguish between the finishes used on different WMT 101 projects.
- Prepare a surface for an oil finish.
- Follow the basic principles of applying and removing excess finish.
- Explain why drying and curing time matter.
- Dispose of oil-finish materials safely.
What an Oil Finish Does
Oil finishes generally enhance the natural appearance of wood rather than covering it with an opaque coating.
After oil is applied, you may notice:
- darker or richer color;
- stronger contrast between earlywood and latewood;
- more visible figure;
- deeper-looking grain; and
- increased visual variation between heartwood and sapwood.
This is why flaws that were difficult to see during sanding can suddenly become obvious.
Not All Oil Finishes Are the Same
The term oil finish covers several different products.
Some are primarily oils.
Others contain oils combined with waxes, resins, solvents, or other ingredients.
These products may have very different:
- application methods;
- drying times;
- number of coats;
- durability; and
- maintenance requirements.
Do not assume that the instructions for one oil finish apply to another.
Follow the product directions and your instructor's demonstration.
Cutting-Board Finish
The cutting board receives a food-safe oil finish supplied or approved for the project.
Mineral oil is one suitable example.
The finish should be applied to:
- both faces;
- all edges;
- end grain; and
- the inside of the handle opening.
End grain may absorb finish more quickly than the faces and may require additional attention.
The goal is even coverage throughout the board.
Furniture Oil Finish
Projects such as the tool tote may receive an instructor-supplied oil finish, such as Osmo or a similar product.
These finishes are used differently from mineral oil.
The exact procedure depends on the product being used.
Your instructor will demonstrate:
- how much finish to apply;
- what applicator to use;
- how long the finish should remain on the surface;
- whether excess must be removed;
- how many coats are appropriate; and
- how long the finish must dry or cure.
Thin and Even Is Usually Better
With many oil finishes, applying excessive material does not improve the result.
Too much finish can:
- remain sticky;
- dry unevenly;
- collect in corners;
- create shiny patches;
- lengthen drying time; and
- require additional cleanup.
Apply the finish as demonstrated rather than trying to build a heavy layer.
Watch Corners and Details
Finish can collect in:
- inside corners;
- grooves;
- joinery;
- routed profiles;
- around screws or plugs; and
- other recessed areas.
Inspect these areas before leaving the project to dry.
Remove excess finish as directed.
Allow the Finish to Dry
Drying time is part of the finishing process.
Do not apply another coat simply because you are ready to continue working.
Allow the finish to dry or cure according to:
- the manufacturer's instructions;
- the shop conditions; and
- your instructor's directions.
Temperature and humidity can affect drying time.
A finish that feels dry on the surface may not yet be fully cured.
Do Not Rush the Last Step
Finishing often happens near the end of the semester when students are trying to complete projects.
That is exactly when rushing can create problems.
Putting a project away too soon, stacking finished parts together, or adding another coat before the previous one has dried can damage work that took weeks to build.
Give the finish the time it needs.
Oil-Finish Rag Safety
Materials containing drying oils can generate heat as they cure.
If oily rags are piled together, that heat can build and create a spontaneous-combustion fire hazard.
In the WMT lab:
Rags or other materials that have absorbed oil-based finishing products must be placed in the approved red metal waste container with a lid.
Do not:
- leave oily rags on a workbench;
- stuff them into your project;
- put them in your bag;
- pile them together; or
- place them in an ordinary trash container.
Follow the finishing-area procedures demonstrated by your instructor.
Maintain the Finish
Some oil-finished objects can be refreshed later as the surface becomes worn or dry.
The appropriate maintenance depends on the original finish.
Before adding another product, identify what finish is already on the object and make sure the products are compatible.
For a cutting board, maintenance may simply involve applying additional food-safe oil when the wood appears dry.
The Finish Should Support the Wood
Finishing is not about making every piece of wood look the same.
A good clear finish allows the characteristics you selected earlier in the project—grain, figure, color, and texture—to remain visible.
The work you did selecting lumber, laying out parts, shaping, and sanding should still be evident when the project is finished.
Check Yourself
- How can an oil finish change the appearance of wood?
- Why should you not assume all oil finishes are applied the same way?
- What type of finish is used on the cutting board?
- What type of finish may be supplied for the tool tote?
- Why can applying too much finish create problems?
- Why must drying time be respected?
- Where must oil-finish rags be disposed of in the WMT lab?
- Why can oily rags become a fire hazard?