A Guide to the Different Types of Varnish

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Proper preparation and application are key for a quality varnish job. Photo by Billy Black

Proper preparation and application are key for a quality varnish job. Photo by Billy Black

A well-done varnish job is one of those things that we have all marveled at—whether it was the hand rail or toerail or some other wood accent on the boat, we’ve asked what varnish was used and what were the application methods. What was the secret? Although there is a resurgence in building wooden boats, the dominant amount of boats are fiberglass and most of the wood used on them, except for the deck, is used as accents. But the reason we varnish those areas remains the same—protection. The reason to varnish any wood is to protect it from the sun, and from water and rot. The secondary reason is to make the wood look good.


Types of Varnish

The first step in the process is to determine what varnish you want to use, and this can be confusing. You may go into a chandlery and ask for a “spar varnish.” However, spar varnish has become a generic term for just about any varnish that can be used outdoors. The term comes from the days when spars were made of wood and ships were at sea. The varnish needed to protect the wood had to be flexible and quick-drying. These early spar varnishes were what was known as “short oil” varnishes, which contained a resin such as pine tar and a small, or short, amount of a drying oil, such as boiled linseed oil or soya. (The terms long, medium and short refer to the ratio of oil to resin in a varnish or other coating.) This fit the bill as it dried quickly, was very flexible and was relatively inexpensive. However, on the downside, these varnishes were not very durable.

Since the time of wooden ships, new resins and oils have been introduced to make varnishes more durable and clearer. Long oil varnishes became more durable, especially when combined with tung oil (or China wood oil), but they were more expensive.

There are basically four ingredients that go into a varnish—resin, drying oil, solvent and additives. The resins commonly used in modern marine varnishes can be an alkyd or a phenolic, or a resin that has been modified with urethane. The top quality varnishes are long-oil varnishes that use either boiled linseed oil or tung oil as a drying oil, but there are still some less expensive varnishes that use other, cheaper oils.

Modern varnishes will also use a good UV package as well as surface stabilizers to protect the wood from the sun. Solvents used are mostly mineral spirits or naphtha (a general term for liquid hydrocarbon mixtures produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat) although there are some blends that will aid with application and help you get a better finish. There are some water-based varnishes, but generally they have lower solids and require about twice as many coats to provide the same protection to the wood as solvent based varnishes.

My favorite varnish is a modified alkyd tung oil varnish, because I like the way it flows off the brush as well as the way it looks after several coats. It has an excellent UV package and is very durable. It is also easy to patch up if it happens to get damaged. Both Captain’s and Flagship varnishes from Pettit, and Schooner varnish from Interlux, are alkyd-tung oil blends.

Taping the area you’re varnishing properly will keep metal and glass clean

Taping the area you’re varnishing properly will keep metal and glass clean

The Application Process

When it comes to varnishing, there is no substitute for good preparation. The signs of poor prep will show through the highest quality varnish. When preparing a varnished surface that is in good shape, remember sanding does not remove contamination. Therefore, the first step is to clean it well by wiping the area with a rag dampened with a solvent, such as xylene or whatever is recommended by the manufacturer, to remove any contamination, then follow with a clean dry rag. After the surface has been cleaned, sand the area with 220- to 320-grade sandpaper. Wipe with solvent again after sanding. You can use a tack cloth to remove sanding residue, but always wipe down with solvent afterward to be certain the tack rag did not leave a residue behind. Apply one to two coats of new varnish.
If the old varnish is in poor shape, it is best to remove it and start from bare wood. Selecting the right equipment can expedite the process. For example, chemical varnish remover loosens thick buildup and allows speedy removal with a wide blade pull scraper. Always use a sharp scraper and slightly round the edge of these tools with a file to avoid gouging the wood. Never file or sharpen a scraper where the filings are likely to end up on an area that is going to be varnished. These filings will turn into rust spots. Sand the bare wood with 120-grit sandpaper to open the grain and help the varnish penetrate into the wood. Also, always sand with the grain.

Keep sandpaper clean and change it frequently. Remember, sandpaper is less expensive than your time. I usually use the 3M-production paper, because that’s what I’ve always used and some things are hard to change. Avoid white sandpaper, as it may have a stearate coating, which can leave a contamination layer that causes the varnish to bubble on application. When sanding edges, use a fine plastic scuff pad rather than sandpaper, because it will remove less varnish. Always wipe the surface with a rag that has been dampened with solvent after sanding to help remove sanding residue.

When making repairs or installing new wood, bed it down so that moisture does not get in and lift the varnish from underneath. A good practice when bedding down trim is to back prime the concealed surfaces with epoxy to prevent moisture from being absorbed into the wood from underneath. Check for moisture in joints. If wood looks black, remove the varnish and use a wood bleach. Then wipe with a fast solvent like xylene to help dry out any moisture, sand the surface and give it a final wipe down with solvent. Apply varnish before the wood absorbs more moisture. Moisture in the wood usually leads to blistering of the varnish.

Varnish not only protects your wood, it can make it look brand new as well

Varnish not only protects your wood, it can make it look brand new as well

Prior to application, pour the varnish into another container. Metal containers are better than paper containers as the latter may have a lining that will affect the way the varnish dries. Make sure the container is absolutely clean: wipe it with xylene to be certain. Once it’s clean, put in some of the solvent that the manufacturer recommends to thin the varnish in the container and then pour the varnish into the container through a strainer. This helps prevent air from getting into the varnish and causing bubbles. Try not to pour out more varnish than can be used in 15 to 20 minutes, because an open container of varnish can also pick up dust or other contamination. The application properties of a varnish that is sitting in an open can will also change over time and you may find yourself adding more solvent than necessary.

The type of brush to use is another hot topic of debate, as everyone has their own opinion. I have a set of badger brushes that I like, but they require a good deal of maintenance. I have also begun to use foam brushes on buildup coats to save time, saving the badger brushes for the last few layers. No matter what type of brush you choose, always clean or rinse it just before starting with the thinner that you will be using in the varnish. That way you start with a clean, slightly damp brush.

It is important to remember that you are applying varnish to provide protection to the wood, so be sure you achieve an even coverage. Apply the varnish across the grain then lay-off the varnish with long strokes along the grain. Hold the brush at 45 degrees. On large areas, a thin foam roller can be used to apply the varnish across the grain, followed immediately with a wide brush to tip it off. Again, remember to go with the grain.
As a rule of thumb, apply a minimum of six coats on bare wood. The first two seal the wood, and will need to be thinned from 20 to 25 percent with the recommended thinner. The next two coats fill the grain, and the last two provide the protection. As the number of coats increases, the level of gloss and protection also increases. I like to use the same varnish for the entire job as this will keep the UV protection all the way from the wood to the finish coat. Sanding between coats ensures that the grain is filled by taking off the high spots and leaving low spots. Sand between the first few coats with 220- to 320-grade sandpaper, but use 320- to 360-grade for the final one. When sanding between coats, remember that you are trying to take off the gloss and remove any mistakes, such as runs or drips. Make sure the previous coat is dry before applying the next one.

A Few Tips

When working outdoors, it is best to varnish in the morning after the dew has dried. Varnishing in the late afternoon or early evening can lead to a loss of gloss and improper drying. Avoid varnishing in the direct sunlight, as this will cause the varnish to dry too quickly. When varnishing interiors, use forced air ventilation to aid drying. Varnish jobs tend to begin to fail at the edges of the wood because there is less film thickness so put extra coats on these areas.

The best advice? Use a top-quality varnish, because your time is more expensive than the varnish, no matter how much the varnish costs.


Epifanes epifanes.com

Interlux yachtpaint.com

Pettit pettitpaint.com

Awlgrip awlgrip.com

Rust-Oleum rustoleum.com

Minwax minwax.com

Sea Hawk seahawkpaints.com

April 2016


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