Cleaning Fiberglass Decks and Hulls


May 31, 2001


The Bottom Line Jealously guarding your boat's appearance will pay dividends at trade-in or resale time.

I believe it is safe to say that a good majority of boat owners are floating fiberglass craft in the rivers, lakes, bays and coastal areas of our fine country. Along with enjoying the benefits that fiberglass offers in strength, rigidity and low weight, the operator of a fiberglass boat will have some work to do in keeping it in like new condition.

Fiberglass has some basic properties that allow it to gather dirt and stains with astounding efficacy. The smooth, outer areas of boat hulls generally have a high gloss gel-coat that would remind one of an automotive clear coat finish. The shine appears impervious, but fiberglass gel coat is notoriously porous. It is also highly susceptible to damage from ultraviolet radiation, and considering the main use of a boat is on the water, it gets baked in the sun all season long. Fiberglass gel-coat also suffers abrasion from floating particles, especially in marine environments, and without proper care it will oxidize quickly. An oxidized finish leaves your boat looking used and long in the tooth.

Fortunately, maintaining the fiberglass boat finish is relatively straight forward. Follow these following steps and you'll have a glowing boat, be it fishing or sporting, for many seasons to come.

Clean boat soon after use: Most of us are trailer boaters, but many have slips or dry store their boats. If you haul your boat out of the water on a trailer, clean that rascal at the first opportunity. If you use a slip, at the least clean your decking and hullsides with soap and water when the day is over. Pay close attentions to stains from fish blood, spilled colas and other substances that have the propensity to transfer their color to the porous fiberglass surfaces. If you haul the boat out, clean the entire boat, bottom to top with soap and water. There are boat soap formulations on the market, but I honestly do not believe they work any better than dishwashing soap. As a matter of fact, I believe the dishwashing soaps work better than many boat soaps. A long handled brush, a short handled brush and a good sponge will make this job easier. Get all hands on deck and soap the whole boat down. Rinse well.

Absolutely clean boat after salt water use: It's hard to emphasize how important this is, but it will have the most bearing on how well your boat will last. Sea salt is very pervasive, and it will infiltrate underdecks, into upholstery and around electronics. It will also ruin brightwork (metal fixtures), even if they are stainless steel. Do yourself a favor and get all hands on the boat and really give it a good going over after operation in marine environments.

Stain removal: You've probably seen a nice scum line around the waterline of your hull, especially after long hours of slow operation and trolling. Trolling and long periods of engine idle will allow underwater exhaust gasses from the foot of your outboard or sterndrive to gather around the waterline. Turbid water, red tide, and other environmental factors will also contribute to this condition. Many times the scum line is created or can be attributed to microbial growth on the hull. This can happen in a matter of hours. My advice about stain removal is to start with the least powerful cleaner and then escalate to the more serious chemicals if your earlier efforts are in vain.

A good, general purpose cleaner that will make quick work of dirt and things ground into the deck is called "Greased Lightning", and is available at Wal-Mart. This stuff can be sprayed liberally about the boat, and when a scrub brush is applied to treated areas, you can get most routine stains off the surface, including tough fish blood and goo. Greased Lightning will not remove scum line. After soap has proved futile, try this product. It is not very expensive, I buy it for around five dollars a gallon. It also has many lateral uses around the home.

If your Greased Lightning didn't get the stain out, now you're getting into some seriously stained fiberglass. Not to fret, though, there are many products available to you. Most hull cleaners are a solution of oxalic acid, and trust me, it will get your stains out with no scrubbing, and almost no work. The down side is that you are introducing a serious chemical into your environment. With that in mind, the best advice is to use it sparingly and in accordance to the instructions supplied with the product. The use of gloves is recommended, but what I do is apply it using a spray bottle. Using a spray bottle allows you to avoid skin contact with the acid. You simply coat the stained area and rinse well with fresh water. Rinse liberally, because the added water will help dilute the solution and make the run-off less of a concern. A good product that I have used is called "Star brite" hull cleaner. Hull cleaners like this would be in the same category as toilet bowl cleaners, and I have known some people who have used toilet bowl cleaners and muratic acid with similar results. Oxalic acid penetrates the gel-coat pores and all stains disappear, period.

Seal it up: Choose a good fiberglass wax and seal up the job. After using heavy chemicals, this step is even more important. Automotive waxes seem to work pretty well, and high quality boat waxes are very good. Mequiar's Flagship is very good but very expensive. There is also a relatively new product on the market called "Woody Wax" which is a spray on product that will seal up the boat. Woody Wax is a bit pricey, but I plan to try some in the near future. Waxing provides two benefits; the most important is a UV layer that will help stave off oxidation and other stains making the boat easier to clean, and the side benefit is that your boat will look great!

The most important ingredient? Diligence. Clean the boat thoroughly as soon as possible after use. Remove the stains as they occur, don't let them build up. Wax the boat, and keep it clean during the off-season as well. Many people allow boats to gather dust during idle periods, but it is a good idea to keep up with it. A cover will also go a long way in keeping the boat ship shape.

So there you have it, guard the boat's appearance jealously and you'll reap the rewards at resale or trade-in time. Besides, you'll look great while out and about.

Tight lines and high tides!

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