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- Finishing Touches: Oil finishes on marine interiors August 2, 2018
I’ve been working on interior marine finishes lately, sorting out what our preferences will be for the new boat. Our last boat, Phoenix, had a mahogany interior and everything was varnished in the traditional marine way with a high-gloss varnish. Eurybia has a teak interior and a subtle rubbed finish that has become popular in boats built in the last few decades. This look is acquired with oil finishes. Here are some images that show the difference between the two finishes.
In this article I am not discussing exterior finish options. For exterior mahogany or teak I would use varnish, as it’s the only real protection for UV and salt exposure and I think it looks fabulous. However inside the boat UV is less of an issue and we can consider both aesthetics and maintenance ease when deciding what to do.
Teak oil, tung oil, and walnut oil are some of the oil finishes commonly used to treat interior wood finishes. Oils creep deep into the wood, providing a thicker layer of protection, increased water resilience and that deep, translucent finish second only to varnish surfaces. These types of oils cure on contact with the air to create a protective film. This is different from mineral and cooking oils which never entirely dry and indeed can be washed off with soap and water. They are adequate for cutting boards or other small items but should not be used on the surfaces of your boat.
There are also wax-based finishes such as products with beeswax, but wax sits on top of the wood and does not penetrate. Also note that oil cannot be applied on top of wax finishes (although the wax can be removed with mineral spirits). For this reason I would not use wax finishes on the boat, although they are frequently used in furniture finishing.
Any of the oil finishes commonly used on boats (Teak, Tung, Walnut, Watco or Danish and others) can successfully be used on your boat. All are easy to apply and reapply with lint-free clothes or rags. Note that the surface has to be clean, dry, and smooth. If it is new wood it should be sanded to 120 or 220 or more. In general you apply oil with a rag or foam brush, wait ten minutes or so, then use a clean rag to remove the excess oil. Repeat in 24 hours if you want a richer finish. You can also sand in the oil with fine 220-grit or so wet-dry sandpaper to get maximum penetration and smoothness.
Note also that the substance called Danish oil or Watco oil is really an oil-varnish mix. It is also applied like these other oils but have read that it’s not as tough or water resistant as tung oil, and takes longer to cure, so I have not included it here.
So if we are using oil finishes, what oil should we use? Here are some notes on several popular oil finishes so you can decide for yourself.
Teak Oil is a great product that provides some protection for your interior woodwork. It tends to be rather thin and drippy and will stain fiberglass and ceiling materials if you are not careful to clean up the drips. I have only used Starbrite, which is quite thin, almost watery. Daly’s SeaFin Teak Oil is reputed to be a little thicker. It has little or no smell, even while working with it, which may be significant to you. It is not food safe so should not be used on cutting boards or tables. Also remember that once a surface is treated with teak oil it cannot be reliably glued.
Tung oil, made from the seed of the fruit of the tung tree, penetrates more deeply and provides more water protection than teak oil. It is also thicker and easier to control when applying – fewer drips. It comes either as 100% Tung Oil (recommended) or in a proprietary mix with varnish and possibly substances to make it dry faster. I will talk below about 100% tung oil, but if you get the other kind just be aware that it must be wiped off in about 10-15 minutes (read the label) and if multiple coats are applied, or if you wait too long to wipe it off, it can take on a satin sheen like varnish. It also has a strong varnish smell unlike the pure tung oil.
Pure tung oil has only a slight smell when applying and the smell fades to nothing as the oil cures. For a light coat just use a soft cloth, but for heavier application on drier wood a foam brush is easier. After an hour of curing wipe the excess off with soft cloths. Two coats are recommended, separated by 24 hours of drying, but for maintenance coats you may find one coat is sufficient.
Tung oil is similar to the less expensive boiled linseed oil (BLO), but dries faster, is more water resistant, doesn’t yellow, doesn’t mildew and is food-safe. This is the finish we have selected for Eurybia. It gives the best performance and yet is easy to apply.
Walnut Oil is a lovely oil but not as robust as tung oil. It is considered a semi-drying oil so doesn’t form the protective film that tung oil and teak oil do.
Comparison of Oil Finishes
Characteristic Teak Oil Walnut Oil 100% Tung Oil UV Protection Yes No Yes Water Resistant No No Yes Food Safe No No Yes Tendency to Drip High Med Low Level of Protection Med Low High
Varnish has the advantages of being very easy to keep clean and of being tougher than oil finishes. For interior use it will not need renewing for years, depending on the amount of UV and water that it is exposed to. We have chosen to use it in the boat for high-touch areas such as the bezels around the touch-to-switch light fixtures. Cabin soles (floors) are another area where the toughness of varnish is useful, but perhaps polyurethane, which is even tougher, is recommended. That’s a project I hope to get to within a year so I will report more then.
Although varnish lasts for years on the interior, 10 or more years of neglect can result in unsightly areas where the varnish yellows, bubbles, and lifts. If you can reapply a new coat every year or so you can avoid this, but when it goes bubbly and yellow you will need to get out the heat gun and start over. Varnish is difficult to apply with 5 or more coats required and 24 hours curing between each coat. Varnish also takes a delicate touch to apply without drips or skips. Also you cannot easily spot-apply varnish to areas that show more wear over time – you usually need to re-varnish the entire surface. However there are few jobs with a higher wow factor at the end.
If you are interested in learning to apply varnish, please read my article on varnishing.
Oil and varnish finishes bring our wood to life and protect it from dirt, discoloration, and wear. They are all easier to renew than to start over so get those rags out and feed your wood!