Offshore Log: Gelcoat Maintenance

In search of the eternal gloss...


Painting fiberglass boats is a huge business. The development of high-gloss, long-lived polyurethanes means you can get multiple years out of a paint job. But a good paint job can be breathtakingly expensive, and a single careless docking can mar that beautiful finish. Better by far is a program of gelcoat maintenance that preserves the finish your boat came with for as long as possible. Whether it’s topsides or superstructure, your gelcoat surfaces will last a long, long time if properly cared for.

Here’s the regimen we developed to care for Calypso’s topsides. It is labor-intensive, but can easily be adopted even by inexperienced sailors. All the materials are available at marine stores anywhere in the world. You will use less than $100 in materials a year with this program, but don’t bother putting a price on your labor.


The first step in any topside maintenance program is to remove dirt and salt. When Calypso arrived in Oman on the Arabian Peninsula after crossing the Indian Ocean, she was so encrusted with salt that you could literally scrape it off every exposed surface of the boat with a putty knife. Unfortunately, salt attracts dirt, so after our first Middle Eastern dust storm the boat was a pretty sad sight, more reddish-brown than sparkling white.

With any luck, you won’t be faced with this type of mess, particularly if you have little water to spare to clean it up, as we did. However, any dirt and salt left on any gelcoat or painted surface will hasten its demise.

Start by washing the topsides with a powerful cleaner-degreaser such as Simple Green. We use a very concentrated solution at this stage, scrubbing hard with a clean, large sponge.

Rinse this sponge often in a separate bucket of water so you’re not just moving the salt and dirt around on the surface. Rinse the surface thoroughly with clean water, and wipe relatively dry with a synthetic chamois or clean towel, just as you would do if washing a car. Drying will minimize water spotting.

Salt Removal

When the topsides are dry, inspect the surface for residual salt or mineral stains. These will be obvious on dark surfaces, less so on white ones. It is critical to remove these deposits before going further. If you don’t get them off, the surface will look dull and spotty, even after polishing and waxing. If you wax over salt deposits, they will be even harder to remove in the future.

We have tried every packaged and home-grown remedy in the world for removing salt deposits. Hands down, the thing that works best is straight white vinegar. It is cheaper and more effective than any mineral deposit remover you can buy.

Wash the topsides with vinegar, rubbing hard with a sponge. You can spray it on from a spray bottle, or simply sponge on out of a bucket. In either case, a lot of rubbing is called for, and you may have to go over some areas several times.

Vinegar is cheap. Use plenty.

Rinse off with clean water when finished, and hand dry with a towel.By this time, you will smell like a large Greek salad unless you’ve worn a good pair of rubber gloves.

In Marmaris, Turkey, we couldn’t find white vinegar—only red wine vinegar. I’m sure the girl at the market thought I was stark raving mad, as my purchases that day consisted of two gallons of red wine vinegar and a case of beer.

After you’ve finally dissolved all the salt, wash the topsides again with a more dilute solution of Simple Green or any boat soap. Rinse again, but don’t bother drying.

Acid Washing

Now it’s time to remove surface stains. For this job, wear both good-quality rubber gloves and eye protection in the form of goggles or safety glasses. Goggles provide better protection from splashes.

Acid washing removes both general discoloration and rust stains from gelcoat. On colored gelcoat, test a small section before slathering the entire surface, just to make sure nothing strange happens.

In New Zealand, we discovered Grunt, a gelled solution of mild acids that is thick enough to cling to vertical surfaces such as topsides, and works brilliantly. Unfortunately, you can’t find it once you leave Asia.

The closest thing we have found in North America is Davis FSR, a gelled oxalic acid cleaner that works almost as well, and is available at any marine store. Buy the large size—you’re going to need it.

FSR is fairly liquid, but holds reasonably well on vertical surfaces. Apply with a natural-fiber brush—the cheap variety—to the entire topsides. We decan’t a half pint at a time into a plastic tub, and paint it on. Spot application, such as to a rust stain, may lead to a mottled appearance. Application to the entire surface will yield more consistent results.

Don’t be afraid to get this stuff on stainless steel. It can also be used to remove surface oxidation from stainless.

Although FSR is fairly mild, keep it off paint and varnish as much as possible, as it may dull the surface. It’s really a gelcoat cleaner. In our experience, it may take 10 minutes or more for FSR to do its thing. Then, it’s more of the ubiquitous diluted solution of Simple Green and a clean sponge to wash the acid off the surface. Rinse thoroughly with fresh water.

If you’re lucky, all the stains have disappeared. Some rust stains, however, may require several applications, so be patient.

If a stain isn’t getting any lighter after three applications of FSR, it’s time for the big guns. Marykate On&Off is a fierce liquid cleaner containing both oxalic and hydrochloric acids. Because it’s a liquid, it does not hold to vertical surfaces. Instead, you must keep brushing it back on before it runs off. Work only on a single stained area at a time. Do not get this stuff on paint or varnish. We can tell you from bitter experience that it will damage these surfaces. It should be used locally, and only on difficult stains on white gelcoat that have not been fully removed by milder methods. Test an inconspicuous spot before using on colored gelcoat.

Once the stain has disappeared, wash the surface completely with boat soap and water, flooding with water to remove all traces of acid.We’d recommend wiping the wet surface mostly dry with clean towels to minimize water spotting, in case your wash water contains a lot of minerals.

At this point, you should have perfectly clean, evenly-colored topsides, probably with a slightly dull finish. Not a trace of old wax will be left on the surface, if there was any to begin with.

Gelcoat Repairs

With the topsides completely cleaned and acid-washed, it’s time to look for areas of gelcoat damage. During six years of cruising, we managed to put a number of dings in Calypso’s topsides, mostly the result of sloppy boathandling when coming alongside, or of rubbing against some shellfish-encrusted piling at low tide.

Once you leave the US, the days of properly fendered docks and pilings are pretty much behind you. You will go alongside rough concrete or timber quays for fuel, waiting in line behind tugs and other commercial vessels whose steel topsides are relatively impervious to damage.

Many of these quays have fendering which consists of huge used tractor tires. Rubbing against these is slightly better than rubbing against concrete. Some quays will have no fendering at all, and your yacht-type fenders, even big ones, may offer scan’t protection. Needless to say, your matching fabric fender covers that look so nice in the marina at home will be reduced to shreds in a matter of minutes alongside one of these beauties, so you might as well leave them behind when you head for foreign shores. We went through three complete sets of fender covers—not cheap—in four years of overseas cruising.

Offshore Log: Gelcoat Maintenance
Waterline stains such as these are easily removed with acid cleaners.

It doesn’t help that many of these fueling locations are in busy commercial harbors which are either exposed to weather or choppy from commercial activity. Many of these docks are marginally suitable for yachts, and a couple attempting to maneuver alongside for fuel will be hard-pressed to keep from dinging the topsides at some point. This is a major reason that cruisers often refuel using jerry jugs, no matter how tedious that may be.

Fortunately, simple gelcoat repairs are not beyond the capabilities of most sailors.

By the time you’ve cleaned your topsides thoroughly, you’ll be intimately familiar with every flaw. Whether you’re doing patches yourself or deferring to a professional, flag every candidate for repair with a small piece of exterior-grade blue masking tape. Don’t put the tape over the ding. Put it alongside, so there is no adhesive transfer into the area to be repaired.

At this point, your topsides may look like they’re covered with blue confetti, but by locating and cleaning each ding, you’ve actually done a good portion of the repair.

We’re not going to elaborate here on the nuts and bolts of gelcoat matching, blending, and fairing, as that’s a major topic itself. Suffice it to say that the time or money you spend on the repairs will be worth it in the long run.


At this point you have perfectly clean topsides with gelcoat dings repaired, and it’s time for polishing. Polishing is a critical step. Each time you polish the topsides you remove a thin layer of gelcoat. Like Goldilocks in the search for the perfect bowl of oatmeal, you must strike a balance between polishing too much or too often—wearing through the gelcoat too quickly—and not polishing enough, so that the topsides remain dull.

If you’re off on a long-distance cruise, high-gloss topsides can go on the back burner until you get home. If that’s the case, you can skip this step and go straight to waxing. Remember, however, that wax alone will not provide you with ultimate gloss. If the gelcoat beneath the wax is dull, the finished surface will not be as glossy as it could be.

Hands down, the finest polish for topsides we have ever used is 3M Finesse-it II. This is a white liquid containing very fine abrasive particles in suspension. It is designed for removing micro-fine scratches and surface flaws from automotive finishes, and works equally well on gelcoat. Since it contains no silicone, the surface is uncontaminated after polishing—key for automotive finishes, which will subsequently be clear-coated.

It may not be abrasive enough for badly oxidized surfaces, but start with this before going to a more aggressive cutting compound.

As is the case on many boats, Calypso’s topsides are gelcoat, but her wide sheer stripe and boot stripes are Awlgrip polyurethane. Eventually, even an Awlgrip surface becomes dull, and must be polished out. Remember, however, that polishing works by removing oxidized surface, whether it’s gelcoat or paint.As long as the painted details are still glossy, don’t polish them. The resin-rich surface which gives polyurethane paint its high gloss is destroyed by polishing, leading to an endless cycle of polishing and waxing which will ultimately wear through the paint.

However, you can’t always afford to mask off painted areas when polishing, since the tape may pull paint off when you remove it. It’s sort of a damned-if-you-do, damned-if-you-don’t situation.

In practice, by the time your gelcoat need polishing, chances are your paint details will be dull as well, and will need the same polishing as the rest of the topsides.

You can polish by hand, or by using a slow-speed electric or air-powered buffer. If you’re doing this job with the boat in the water, using an electric buffer is dangerous, and is not recommended. If the boat is hauled out on dry land, electric tools are fine, as long as you’re using a power cord equipped with a ground fault circuit interrupter.

A polisher runs at relatively slow speed to keep the surface and the polishing products cool. Surprisingly, the polishing bonnet itself makes a big difference in the job. The 3M Superbuff pad works extraordinarily well. If you are power-buffing, remember to use separate pads for the polishing and waxing stages for best results.

We have, on more than one occasion, hand-polished our topsides, both from the dinghy and from alongside floating docks. This is tedious in the extreme, to say the least., and does not do as good a job as power buffing. On the plus side, you’ll end up with shoulders like Hercules. You may also end up eating aspirin like candy.

Use only clean all-cotton rags for hand polishing. Finesse-it is really designed for power polishing, but you can certainly use it for hand-polishing if necessary.

We buy large packages of polishing rags from auto supply stores or marine stores, storing them in plastic zipper bags on the boat. As the rags get used up, they are plunked into a bucket of soapy water, and washed out at the end of the day for use again the next day. For both polishing and waxing, an endless supply of clean rags is essential.

You must be systematic in your polishing. We use blue masking tape to delineate the area we’re working in, generally polishing an area about three feet long by the height of the topsides. Don’t look at all the area you still have to do—just concentrate on one zone at a time.

Work from the top down, doing the area around the waterline last. Heel the boat to the opposite side by shifting weight if necessary to get the boot stripe well clear of the water.

It may be possible to mask the top of the bottom paint, or just do the waterline freehand, working carefully. We generally keep a separate rag for doing the waterline area, as we inevitably swipe the bottom paint at some point, or accidentally dip the rag in the water. Once it’s wet with salt water, the rag cannot be used further without a thorough washing.

Within our masked-off area, we generally do about one square foot at a time, working from the already-done part of the topsides into virgin territory. It’s important not to let the polishing compound dry on the surface before it’s buffed out, or it simply won’t do its job.

This clearly isn’t rocket science, but technique does make a difference, especially when hand-polishing. It’s all too easy to miss areas or do a less-than-thorough job.

Offshore Log: Gelcoat Maintenance
Exhaust smoke on poorly sealed gelcoat will leave stains that are difficult to remove.

After polishing each square foot or so, we take a clean dry rag to buff the area, checking for residue and missed areas by sighting along the topsides at an oblique angle.

Did I mention that this is tedious? Our high-sided 40-footer has a total of about 350 square feet of topsides. If it takes about one minute of polishing per square foot—allowing a little bit of resting time here—that’s a total of six hours, or just about a full day. You will be very, very tired by the end of that day. This is when a portable CD player attached to your belt is worth its weight in gold. Don’t forget to wear a good hat and sunglasses as well, as the glare off white topsides can be blinding.

At this point, your topsides should have a high, nearly flawless shine. Go back over any areas you’ve missed, or places that need additional attention.It’s important not to leave the polished surface unprotected any longer than necessary, for topsides get dirty quickly. In fact, we usually finish one entire side, polishing and waxing, before tackling the other side. One long day—a very long day—is required for each side of a 40-footer.

Somehow, having one side completely finished gives you the spirit you need to complete the rest of the job. The contrast between the finished and unfinished sides is a reward in itself. It also gives you a little bit of breathing room if you need a day’s break to give your tired muscles a chance to recover.


Waxing is very similar to polishing. We use a hard paste wax, working in exactly the same systematic method as is used in polishing. Collinite Fleetwax is our favorite.

Use a damp sponge applicator for the wax, and cotton rags for the final buffing when doing the job by hand. If you got a kick out of waxing the family car as a teenager, you’re really going to love waxing your boat. If you hated it then, you’ll hate it now.

As obvious as it may seem, read the directions on the can. Some waxes must be left to dry to a haze on the surface before buffing. Others must be buffed off before they dry, or they will be virtually impossible to remove.If possible, time your work or position the boat so you can work in the shade, both to keep the surface cool and to keep from going blind. This may mean working in early morning and late afternoon, not in the heat of the day.

At this point, knowing exactly what zones have been completed is essential, for there should be little or no difference in the appearance of areas that have been polished, and those that have been both polished and waxed. Polishing provides the gloss, wax provides the protection. Polishing without waxing is a waste of time, as is waxing without polishing if your topsides are dull. The exception would be a pure maintenance waxing while you’re out cruising, just to protect the gelcoat.

A boat that is in year-round service in the tropics should be cleaned and waxed at least twice a year. Every time you wash the topsides with detergent, you remove wax. Leaving topsides dirty, however, is a bad alternative. If you keep the topsides waxed, you may go several years without polishing. Polishing keeps the topsides looking good, but gradually wears away the surface.


This entire regimen is much easier to do with the boat hauled out and with proper staging. It will take about twice as long to do the job by hand as it will using a proper power buffer. If you’re off cruising, however, doing the job by hand from the dinghy or dock may be the only alternative.

Unfortunately, topside maintenance doesn’t necessarily wait until your next haulout. You may get a few more months out of your bottom paint by cleaning the bottom more often, but you can’t squeeze a few extra months out of a topsides wax job. Sun and salt take their inexorable toll.

Is it worth it? Professionally painting the topsides of a 40-footer may cost anywhere from $5,000 to infinity, depending on where you are and the quality of the job. Once you paint, there’s no turning back. Even the best paint job may need to be renewed every five years or so.

Although we’ve talked about topsides here, the same regimen applies to other exposed fiberglass surfaces. The exception is areas of molded-in non-skid, which should be cleaned but not polished or waxed.

If you start with new gelcoat, or a boat that is only a few years old, you can easily get 10 years or more out of the gelcoat before you’ll need to paint. We have seen carefully-maintained 15-year-old gelcoat that looks just like new, even though the boat is in year-round use.

White gelcoat lasts the longest, as irregular fading is not quite as apparent as it is with colors.

The keys to gelcoat maintenance are: keep it clean, keep it waxed, and repair dings in a timely fashion. Polish no more frequently than is absolutely necessary, and then use the least abrasive material that will do the job.

If you get to the point where you need to use rubbing compound rather than polishing compound to remove oxidation and restore gloss, you’re not washing and waxing frequently enough.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at