Many woodworkers consider woods with a high oil and rosin content to be among the most beautiful materials available, but finishing oily woods has historically been a challenge to accomplish properly and safely.
While the correct surface preparation of the selected wood species is important, the methods of preparation come from various schools of thought.
Traditionalists tend to resort to cleaning the wood multiple times with acetone or denatured alcohol before and after each milling and sanding procedure (to remove the inherent oil), sealing it with dewaxed shellac, and finishing it with nitrocellulose lacquer, penetrating oil-varnish, or 2K catalyzed finishes.
These processes bring several safety factors into focus – In addition to the array of chemicals used to clean and neutralize the oils – let alone the chemical composition of the solvent-based finishes, many being highly flammable, finishers are exposing themselves to the dangerous toxins found within the wood species itself.
I’m happy to report there is now a safer, highly effective, water-based way to finish oily woods and other challenging substrates. (Spoiler alert: see EMCAT+ Si427 Sealer Isolator.)
More on that in a bit.
To understand the full picture, here’s what you need to know about working with and finishing oily woods.
Common Oil-Rich Wood Species
The term “oily woods” refers to several exotic hardwood species that contain naturally high levels of oils and resins within their cellular structure. The most commonly used oily woods include:
• Teak: Perhaps the most famous oily wood, prized in boat building and outdoor furniture
• Ipe (Brazilian Walnut): An extremely dense South American hardwood
• African Rosewood: Various species known for their rich, vivid colors
• Cocobolo: A tropical hardwood with striking grain patterns
• Babinga: Known for being troublesome when finished with oils
• Brazilian Walnut: Not to be confused with American Black Walnut
• Curupay: A South American wood species used in the flooring industry
These species are typically tropical or subtropical in origin, which explains their high oil content – it’s a natural defense mechanism against decay and insects in their native humid environments.
Benefits of Working with Oil-Rich Woods
Despite the challenges of finishing oily woods, they offer several significant advantages that make them highly desirable for specific applications:
1. Natural Weather Resistance: Their high oil content provides excellent protection against moisture, rot, and decay, making them ideal for outdoor projects and marine applications.
2. Durability: Most oily woods are extremely dense and hard-wearing, often lasting decades with minimal maintenance.
3. Insect Resistance: The natural oils act as a deterrent to wood-boring insects and other pests.
4. Dimensional Stability: These woods tend to experience minimal movement with changes in humidity, reducing the risk of warping or cracking.
5. Beautiful Aesthetics: Oily woods typically feature rich colors and striking grain patterns that can be enhanced to create stunning finished pieces.
Historical Finishing Challenges
The characteristics that make oily woods desirable also create significant finishing challenges and explain why special preparation techniques have historically been necessary.
Whereas domestic hardwoods and softwoods readily accept finishes through absorption into the wood fibers, oily woods present unique challenges because:
• The natural oils prevent proper adhesion of many finishes
• Traditional oil-based finishes often remain tacky or fail to cure properly
• Conventional water-based finishes tend to blush on the surface
• The oils can continue to seep out of the wood over time, causing adhesion failure
• Temperature changes can cause the oils to become more active, leading to finish degradation
These challenges led to the development of specialized preparation techniques and finishing products specifically designed for oily woods.
Part 2: Preparation, Sanding and Sealing Oily Woods
Preparing oily woods for finishing was historically labor intensive, but the extra effort was essential for achieving desirable results.
The traditional preparation process included…
1. Surface Cleaning: wiping the wood with acetone or naphtha to remove surface oils.
2. Sanding: progressively sanding and cleaning between grits.
3. Final Oil Removal: wiping again (and again, and again, etc.) with acetone, lacquer thinner, or denatured alcohol.
4. Sealing: applying a coat (or coats) of dewaxed shellac.
If that sounds like a lot of work…it was.
Thankfully, there is a newer, safer and faster way to prepare and seal oily woods.
In late 2024, we introduced EMCAT+ Si427 Sealer / Isolator, a water-based, self-leveling sealer and barrier coat designed specifically for use on difficult-to-cover substrates like oily woods and previously-applied coatings.
See, EMCAT+® Si427 features a unique ionic charge that allows it to bond to a wide variety of properly prepared substrates including all types of wood surfaces (oily, exotic hardwoods, veneers, engineered wood products, etc.), and a wide variety of natural and synthetic surfaces such as stainless steel, stone, plastics, and fiberglass.
This makes the process of sealing oily woods MUCH faster, easier and safer. All you need to do is…
1. Clean the wood surface with denatured alcohol or clean water
2. Sand to 180-400 grit based on your desired finish.
3. Apply Si427 via spray (rolling or brushing is recommended only on small areas)
By the way, EMCAT+ Si427 can also be used as a Sealer/Isolator over select fire retardant coatings without the concern of haze or chemical blush in the topcoat (I’ll cover this in detail in a future post).
The final step in finishing oily woods is, of course, top coating, which we’ll discuss in Part 3.
For now, I’d like to ask you: do you have any experience or advice with respect to finishing oily woods? Please share your thoughts or read what others are saying in the comments section below.
Jeff Weiss is the owner and chief chemist at Target Coatings, which has been dedicated to exclusively manufacturing water-based, low-VOC and HAPs-free wood finishes for nearly 40 years. Creator of the first water-based lacquer with 100% burn-in rivaling nitrocellulose lacquer, Jeff is considered one of the “founding fathers” of water-based technology and safety for refusing to accept the “status quo” and for refusing to expose others to chemicals he wouldn’t want to be exposed to. A U.S. Air Force veteran and former volunteer EMT, Jeff has always put service and safety first. Outside of work, Jeff is an avid fly fisherman who enjoys being immersed in and inspired by Earth’s natural beauty.
