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Boat Varnishing Tips

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Tricks of the Varnish Trade

Want your varnish to shine like the July sun?
Here are 10 tips to help you out.

scraping wood on boat

Brilliant-looking brightwork is something nearly all boaters admire, but few seldom achieve. The best way to achieve it, if you have vast expanses of shiny wood, is to hire a pro, but most boats have only varnished details: Cabin eyebrows, handrails, a teak toerail, trim around the pilothouse windows—small stuff that’s DIY manageable. And there are a variety of tricks of the trade that the pros use to make even small varnish jobs a little easier, and the finish a little brighter. Here are ten you might want to use:

Don’t Dillydally
Maintaining varnish isn’t onerous as long as you keep ahead of its inevitable decomposition, so bite the bullet, or the sandpaper, and get ’er done sooner rather than later. If the varnish is still intact, just lay on more coats after lightly prepping the surface. There’s no stripping required, no heavy lifting with paint remover or heat guns or two-handed scrapers. It’s almost a pleasant chore if you’re in a contemplative mood. (If you’ve let your varnish go to pot, however, read “Secrets of a Stripper”, then limber up your checkbook.)

Start with Soap
Before folding your first sheet of sandpaper, wash your brightwork thoroughly; no sense sanding dirt. And if you’ve been sloppy with wax, use a solvent to clean any excess off the brightwork; otherwise, sanding will drive the wax into the varnish, and when you lay on your next coat you’ll have more fish eyes (unsightly bubbling up or pulling away of your varnish) than an aquarium. Denatured alcohol should do the trick.

Scrape and Spot
Yellow patches in the old finish are evidence that water’s gotten under the varnish and lifted it, says refinishing pro Tobi Keitmeier ( Scrape away the damaged varnish, using a light touch on a razor-sharp scraper—you want to remove the bad varnish without damaging the underlying wood. Then sand the area with 220-grit sandpaper, wipe away all dust (use a rag with the thinner recommended by the varnish manufacturer, although denatured alcohol works, too) and apply at least one spot-coat of varnish to seal the wood. Classic oil-based spar varnish is best, adds Keitmeier: It adheres well to bare wood, but can be recoated with polyurethane to create a harder finish. You can use a cheap foam brush for this, and then toss it.

Keep the Scraper Sharp
A scraper is really a two-part tool: the scraper itself, and the flat file you’ll use frequently to resharpen it. Choose a small scraper with easily replaced 1- or 1.5-inch blades; you’ll probably pay more for the file than the scraper. When you sharpen, move off the boat, or metal filings will stain the deck when they rust. Be sure to sharpen across the entire blade, corner to corner; otherwise you’ll create a concave cutting edge that will damage the wood. If your scraper’s edge develops a hollow, replace it; blades are cheap.

Scratch the Surface
Sanding not only provides better adhesion, and smoothes and cleans the surface, but also forces you to make a thorough inspection of said surface that often reveals issues—old brush marks, runs, dead bugs, etc.—you hadn’t noticed before. Use 220-grit sandpaper, or a Scotchbrite pad, or even fine bronze wool to knock the gloss off the surface; you want it universally dull. I think sandpaper does the best job. After you begin laying on your varnish, switch to 320- or 400-grit paper between coats.

If you have lots of flat areas, a sanding block helps, but don’t use a stiff block on curved surfaces or you’ll take off too much. You’ll find flexible sanding blocks at the chandlery or hardware store, but I’d use my even-more-flexible hand. And take it easy sanding hard corners, or you’ll be down to bare wood before you know it.

Dust and Wipe
Most skippers sand, then wipe down the wood, then brush on a fresh coat of varnish. But they don’t clean the decks around the brightwork, where much of the sanding dust is just waiting to blow onto their nice, fresh, wet varnish. All it takes is a zephyr to ruin a day’s work. Once you finish scraping, spot-coating any bare wood, and sanding, wash the boat to get rid of the dust. Give it plenty of time to dry, which won’t take long in the summer sun, then wipe down the brightwork with a solvent-soaked rag (Keitmeier uses denatured alcohol) or a tack cloth. While everything is drying, mask off your brightwork so you don’t get varnish on the gelcoat.

Buy Good Tape
Leave cheap masking tape on too long and the only way you’ll get rid of it is to sell the boat. Use painter’s tape instead: Keitmeier recommends “14-day” tape; ScotchBlue Painter’s Tape is a good brand, but there are others. I don’t think you want to leave it on for two weeks, but you can leave it long enough to lay on a couple of coats. (Once you take the time to prep and mask the work carefully, it only makes sense to apply two coats at least.)

masking tape

However, even painter’s tape can be hard to remove if you haven’t waxed your boat recently, especially if the gelcoat is badly oxidized. Save yourself some heartache by waxing around the brightwork before starting your varnishing project, compounding first if necessary. Remember the caveat about removing excess wax from the varnish.

Brush Up
Most experts agree that natural-bristle brushes are best for varnish. Keitmeier uses Corona Europa brushes; a 1½-inch Europa, probably as wide as you need for this kind of work, will set you back about $17. Italian-made Epifanes brushes are also excellent, albeit more expensive. Buy good quality brushes and take care of them and they’ll last for years.

Keitmeier always uses a new brush for a finish coat, but only after cleaning it thoroughly several times. A new brush right out of the wrapper is dirty, he says, full of dust and usually pestered with some loose bristles. Once he’s used a brush once, Keitmeier cleans it with mineral spirits, a brush comb, and a spinner, then relegates it to applying preliminary coats. Keitmeier says this avoids the risk of a fleck of dried varnish from ruining the next finish coat. (See “What’s in a Brush” for more advice on brushes.)

Don’t Guess, Measure
Never use varnish straight out of the can, and never use it without thinning. Pour it into a graduated cup that lets you measure the correct ratio of varnish to thinner. What’s the correct ratio? It depends mostly on temperature: An August day in Miami demands more thinner than a brisk September in Maine. (In steamy Florida, you may want to wait until September or October to varnish.) Use the manufacturer’s directions as a start, and mix small batches; if the varnish drags, or sets before the brush marks smooth out, add a little more thinner.

measuring cup

Ditch the Dust
Dust is the enemy of varnish, and it’s a law of nature that as soon as you start laying on the finish coat, the wind will pick up and swirl clouds of marina dust into your work. 

How do you fight this? Take a weekday off and varnish while your marina neighbors are at work. You’d be surprised how much dust is kicked up by the hustle and bustle on the weekend, but things are quieter between Monday and Friday. And you won’t have to deal with as many kibitzers telling you what you’re doing wrong. 

Varnish early in the day, before the sun starts beating down and the afternoon breeze builds. Do your prep the day before (actually, you may have to take two days off), so as soon as the dew has dried off the brightwork, you can give it a final wipe down and start varnishing. This also gets the job finished early, so you can goof off in the afternoon. 

If, despite precautions, you get dust in the varnish anyway, or if you miss a spot, or anything else goes wrong, don’t try to fix it, warns Keitmeier. You’ll just make things worse, so let the work dry and fix it with the next coat. Flow it and forget it, he advises. 

Hey, maybe you’ll have to take the whole week off. Heck, it’s summer—why not?

This article originally appeared in the July 2015 issue of Power & Motoryacht magazine.