Mention to someone that you’re going to varnish your boat and notice one of two reactions: either a glazing of the eyes as fear sets into your listener, or a deep inhale as they prepare to tell you long tales of how to do it “right.” Varnishing isn’t for the meek. You have to be committed when you set about keeping your bright work in Bristol fashion. Although I can appreciate a flawless mirror finish as much as anyone, I believe that this is reserved for high-end antique furnishings rather than for exterior boat maintenance. My first brush with varnishing (pun intended) was really just about keeping the cap-rail protected from UV rays and helping my 30 year-old boat looking her best.

When I bought the boat, I was delighted to see how little exterior teak she had. “Why it’s just a four-inch wide caprail,” I exclaimed happily. “This will be a breeze.”

But the boat was 50 feet long. Multiply that by two sides and add a 12-foot transom and then just toss in a teeny tiny brow rail and I was soon wondering how I became a wood finisher. Nevertheless, I was determined to learn this black magic of wood care and over the years, I graduated from the school of hard (wood) knocks to earn the degree of the non-perfectionist varnisher. Once, as I had just finished a coat that I was particularly proud of, a dock neighbor swung by. He’s the kind for whom anything short of eight coats of deep gloss is just plain failure. He inspected my work by leaning down over the long run of the rail. Then he straightened, sniffed and with kind eyes fixed on me said, “Well, it’s never really the last coat, is it?”

Never the last coat, indeed. So, let's dive into the details.

Here's the basics to varnishing wood on a boat:

  1. Complete prep work: remove old varnish by sanding, rinse down your boat and tape off your area.

  2. Use a badger-hair brush when varnishing.

  3. Apply a thin first coat, and keep a wet edge.

  4. Keep your strokes long and light, brushing from dry back to the wet edge.

  5. Sand in between coats—be sure that the varnish is dry and cured before sanding.

  6. Apply new varnish. Repeat as necessary.

  7. Remove tape—and done!

marine varnish on wooden boats

It’s all in the prep

In any sized job, 80 percent of the work is usually in the prep. Varnishing is no different. As an example, in my 100 feet of caprail, it took two full days of two people working to prep the surface and then three full days to apply three coats (mostly due to necessary drying time). The first two days were tedious if not downright brutal.

If the surface you’re working with has been previously varnished, remove the old varnish with a heat gun, paint stripper or sandpaper. Sanding is an especially hard and messy job but it works if you’re especially persistent. Oxalic acid or bleach will get rid of discoloration and dark spots on the bare wood—just be careful that this stuff doesn’t end up in the surrounding water. Rinse with plenty of fresh water after and sand with 180-grit paper. Then sand again with 220 grit. Then vacuum the surface, change out of your dusty duds and stop sneezing.

Tape off your area with painter’s tape. The green stuff is great but more expensive. The basic blue tape is widely used and can be purchased at a hardware store. Some people tape before they sand which helps protect the nearby gelcoat surface. Connecting long strips of tape and overlapping in the same direction will make removal quicker at the end of the job. Don’t leave tape on for weeks—the adhesive breaks down with heat and UV and it will be a bear to remove it later. Tape when you’re ready to tackle the job and get it done in a week or so.

Some people like to use a tack cloth to do the final wipe down and that’s surely the right way but I find they’re a sticky mess to work with. Wiping the surface down with the appropriate thinner and a lint-free rag works fine for most basic jobs. I like old T-shirts or cloth diapers (no terry towels) to keep things as clean as possible.

The next step is to learn to control the weather because there is such a thing as varnishing when it’s too hot or too cold, and too damp or too dry. If you varnish in wind, your wet surface will attract every bit of dust and airborne crud from miles around. If you’re varnishing outdoors, try to do so in the morning before the breeze kicks up. Don’t add new coats of varnish when it’s foggy or really humid and don’t add coats too late in the day (after 4:00 pm) when they do not have time to dry before the evening dew sets in.

Brushes to apply varnish

Badger-hair brushes are the standard for serious varnishers. They’re worth the high cost because they release varnish evenly and leave few brush marks. They deliver that mirror finish you’re after. With thorough (and I do mean thorough) clean­ing, they can be used for years. Cleaning typically requires 3-5 rinses in clean thinner. Then they need to be spun or slapped to remove the thinner. They then need to be wrapped in a clean rag and hung from a hook until their next use when they’ll need another thinner bath. These brushers are wonderful but they take maintenance and the patience of Job.

Foam brushes are disposable. They don’t hold much varnish and they sag if you get too much in them. You can’t really lean on them in tight corners as they become flimsy and deposit blobs of varnish. They also fill up the landfills. They’re cheap and perfect for small jobs but not great for serious finishes.

The third kind is cheap bristle brushes. They come in various widths for different jobs and hold a decent amount of varnish. They can make a nice even finish if you take the time and use them right. They do shed bristles so you’ll need to be on constant lookout and if you miss one, you’ll need to wait until the varnish dries to gingerly pick the hair out. They’re disposable and found everywhere from chandleries to big box home stores.


Applying protective varnish on a wooden surface. You will need a range of brushes to hand. Image credit: Troyan Photo on Pond5

Painting varnish

After a ridiculous amount of time in preparation, you’re finally ready for the satisfaction of actually varnishing. Thin the first coat (20-50 percent depending on the varnish you’re using and the environmental conditions).  Although it seems counterintuitive to thin the liquid when you’re trying to build up a surface, a thin first coat will cure faster, protecting the bare wood. Thinner varnish also flows better, looking downright elastic as you “pull” it from a dry spot to the wet edge. Use the thinner that is recommended for your particular kind of varnish and not just any old solvent. For uneven surfaces, try sanding with a sanding block rather than your bare fingers and then fill in the low spots with multiple layers of thinned varnish.

Speaking of varnish, it’s not all created equal but if you ask 10 boaters what’s best, they’ll give you 12 different opinions. After much painful trial and error, I chose Flagship because it lasted the longest and produced a finish that was good enough for my cap-rail. Some people insist on Captain’s varnish, which, for me, didn’t hold up as well against UV breakdown. True perfectionists spring for Epifanes. I will readily admit I’m probably not a good enough varnisher to get too picky. Some people swear by the “un-varnish”—Cetol. It’s easy to apply but doesn’t last long and tends to add a lot of tint that looks a bit sickly after repeated applications. Test out a few options and then you, do you.

The wet edge is the front line of the varnish and it’s key. It’s easiest to see on a reflective angle. This changes in bright sunlight and in the flat light of an overcast day. Some folks insist that polarized sunglasses help. I like to varnish without sunglasses, which makes me nearly blind at the end of a sunny day but at last I can see the wet.

Keeping a wet edge, work carefully but quickly. The length of wood you cover at a time will depend on its width – but target about a foot at a time. If you get curtains, drips or sags on a vertical surface, your brush is too loaded with varnish and you’re not getting the right flow. If you get what’s called “orange peel” on a flat surface, the varnish has gone on too thick and has dried poorly. Holidays are dry spots where you can see the brush strokes. When your brush glides easily and leaves no streaks or spots, you’ve got it dialed in.

Keep your strokes long and light, brushing from dry back to the wet edge. Short and choppy painting will pile up the varnish and generally take longer to cover the same area. Don’t over-brush. If you make a mistake, fix it on the next coat because trying to repeatedly brush a dry spot will make it worse.

Never varnish right out of the can. The amount of crud you introduce into your can of expensive varnish will make you sad. I decant into plastic containers I save from soup or cheese so I don’t spend money on the same cups they sell at the chandlery.

Seal the can tightly when not in use. With repeat openings, a can gathers dust and gunk and it’s best to start with the cleanest varnish you can. You may want to use cheesecloth to strain your varnish as you decant. You may need to eventually add thinner because even a well-sealed can will skin over.

Every DIY boater knows that every last coat of varnish is just the coat before the next one.

Sanding in between coats

Just when you thought you were done with all that nasty sanding, you realize that you’ll have to do so between coats to rough up the surface so the next coat adheres better. You may think, “Why sand and take off all that work I just did?” Well, the key is not to sand it all off. Use 320 grit sandpaper for in-between coats or better yet, use a dish scrubber or soft 3M sanding pad to keep as much of the previous coat on as possible. An old-timer once suggested these pads and I’d never do it any other way. Clean your surface as well as yourself before applying the next coat.

The varnish must be dry and cured before sanding—not just skinned over. If it gunks up your Brillo pad or sandpaper, it’s not dry and you’ll do more harm then good. Let it dry, sand, apply new varnish. Repeat. Remove tape.

When you decide you’re done, you’re done. Leave well-enough alone because remember—every coat of varnish is just the coat before the next one.

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Written by: Zuzana Prochazka
Zuzana Prochazka is a writer and photographer who freelances for a dozen boating magazines and websites. A USCG 100 Ton Master, Zuzana has cruised, chartered and skippered flotillas in many parts of the world and serves as a presenter on charter destinations and topics. She is the Chair of the New Product Awards committee, judging innovative boats and gear at NMMA and NMEA shows, and currently serves as immediate past president of Boating Writers International. She contributes to and, and also blogs regularly on her boat review site,