Cleaning Fiberglass Hulls and Decks - SailNet Community
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Cleaning Fiberglass Hulls and Decks

A little time spent maintaining the sheen of your topsides and decks will pay in the long run as it can keep the gelcoat from becoming more porous.

What sailor would rather scrub decks or clean a hull when he or she could be out there sailing? None of us, right? Well, even though fiberglass has been the maintenance-saving answer for many boat owners, itís still not completely maintenance-free. Itís very important that we take care to protect our boatís outermost layer, the gelcoat, from three major assailantsóthe sun, salt, and various forms of stains and dirt. If left to the elements, a shiny boat will soon turn dirty, chalky, and become increasingly more difficult to clean.

When a fiberglass boat is built in a mold at the factory, ordinarily a release agent is applied to the mold, followed by a layer of gelcoat that is sprayed on. Next, layers of fiberglass cloth and matt soaked in resin are applied. Once released from the mold, itís this relatively thin outer layer of gelcoat that provides the hull and deck with color, shine, and smooth good looks, and this is the material we are really dealing with when we talk about cleaning our fiberglass boats.

In this article, we hope to help you maximize your cleaning results while minimizing the amount of time spent with rag or brush in hand. Knowing which products work best for each application and understanding some basics about fiberglass care is the key to protecting the good looks and long life of your gelcoat, and ultimately the value of your boat.

Dirt and Salt    Dirt, grime, and salt all act as tiny abrasive particles on your decks and cabinhouse and should be considered your boatís worst enemy. If left untouched, the simple act of walking about on deck will move around and grind these particles into the gelcoat. This activity will dull the finish of your once-shiny boat, and it can begin to shorten the life of your gelcoat. Salt left on deck can also act as a natural magnifying glass increasing the sunís damaging rays, which will accelerate oxidation and hasten the break down of this surface layer.

The first step in lessening the wear and tear on decks and hulls is giving them a thorough rinsing with freshwater on a regular basis.

Frequently hosing down of your boat with fresh water is the best course of action as it will remove much of the dirt, grime, and salt from the surfaces. Wiping the smooth areas with a rag, and employing a soft bristle brush to coax imbedded particles from your non-skid helps as well. But you should scrub gently though, as even repeated scrubbing motions can shorten the life span of gelcoat. We recommend that you combine your regular wash down with a specially formulated soap made particularly for fiberglass boats like Star briteís Sea Safe Boat Wash. These boat soaps donít remove wax like a high detergent soap, and most are biodegradable.

When boat soap alone provides less than satisfactory results, you may need to resort to other means. First try applying a multi-purpose stain remover like FSR or Y-10 to the afflicted area. If you need even more muscle, cautiously employ an abrasive cleanser like Soft-Scrub or Bar Keeperís Friend. But at all costs you should resist the temptation to over-use these abrasive type cleansers because they strip wax and abrade gelcoat surfaces. Itís easy to get into the habit of using this stuff too much due to the fast results you see, but later on the same area will get dirtier again more easily, and will become progressively tougher to clean due to its increased porosity. Itís really important that you avoid this self-defeating cycle or youíll soon begin to wonder where that nice shine went and why the heck you canít get it back.

Organic Stains    Identifying the source of a particular stain is usually the key to determining how to remove it. A stain that is organic in nature, like one caused by fallen leaves or annoying bird droppings, can be easily removed by applying a diluted bleach solution. Mix one part bleach with one part water and then pour or spray the mixture onto the affected area. We like to use a small spray bottle for easy application, but you should watch your footing as this solution ends up being extremely slippery. After several minutes, rinse the area thoroughly, let it dry, and then apply a new coat of wax. If youíre able to catch these stains early, your boat soap may suffice, saving you the bleach and re-waxing process.

Waterline Stains    In certain bodies of water, boats can develop a terrible stain at their waterline. One place where weíve found this to be particularly true is along the Intracoastal Waterway. All vessels transiting these waters will develop a stubborn brown stain, which can often appear several feet high at the bow and extends aft along the waterline. This brown discoloration, commonly referred to as "ditch stain," can be one of the most perplexing stains to remove. We tried everything: bleach, abrasive cleansers, wax, rubbing compound, etc., all with no luck. Finally one day we discovered the secretóproducts containing acid. Itís not often that you find a cleaning approach that works instantly, but it was a happy day when we did.

Small rust spots like these shouldn't be too much of a concern, but if you find rust in the middle of your cabintop or deck, it's likely that your rig needs inspecting.
To effortlessly remove ditch stain, apply a small amount of FSR, Y-10, On and Off, or Instant Hull Cleaner, and the stain will magically disappear. The blue gel formulas of FSR and Y-10 contain oxalic acid, but are not irritating to use, so we prefer them to the others. A simple bare-handed rag application is OK, but if you choose ON and Off or Instant Hull Cleaner, youíll need to wear gloves, avoid coming into contact with the product, and be careful of the fumes. You will, of course, need to re-wax the hull after applying these products. To make it easier to stay alongside the hull while cleaning from a dinghy, you can use a specially designed handle with suction cups to hold yourself close to the boat.

Rust    In addition to attacking waterline stain, acid-based cleaners are usually the solution for dissolving rust. To remove rust stains from the hull and deck, we again prefer the blue gel formulas of FSR and Y-10. Weíve found each of these safe to apply not only to gelcoat, but also to metal, painted surfaces, and even our synthetic non-skid, Treadmaster. Apply, let sit for awhile, and then rinse thoroughly with water. For stubborn rust, a second application may be needed, or a little soft-bristle scrubbing. For hard to reach deck areas like those around the bases of stanchions, use a toothbrush to coax the gel into the areas.

"To remove rust stains from the hull and deck, we prefer the blue gel formulas of FSR and Y-10, which are safe to apply to gelcoat and don't require gloves."
Another method for removing rust is to use oxalic acid crystals diluted with water. A non-boating product, Bar Keeperís Friend combines oxalic acid with a Comet-like cleansing powder. (This product is available at most grocery stores.) But one final note about rust: Itís considered normal for a small amount of rust to occasionally develop on deck around stainless steel parts. Unexplained and reoccurring specs of rust dotting your cabinhouse and deck are, however, another matter. The likely culprit is your standing rigging. In this case, itís time to institute a rigging check to determine if anything up there needs replacing.

Wax and Polish   One of the most important things you can do to protect your boatís smooth gelcoat surface is to keep it waxed and polished at all times. And if you do this regularly, the surfaces will last longer and be easier to clean and maintain. By keeping small crevices in the gelcoat filled with wax or polish, dirt flows off your boat more easily. You need to be aware that many strong cleaners used to remove stains also strip wax and polish, so always re-polish after heavy cleaning. But donít apply wax or polish to the non-skid areas of your boat though, as this will promote slipping. Just keep these areas clean with plenty of water and boat soap.

If the smooth fiberglass surfaces are not kept waxed and polished, gelcoat can develop a dull, chalky appearance that is due to oxidation caused by prolonged exposure to the elements. This is particularly noticeable on colored hulls. Youíll know that oxidation is in its initial stages when you first notice your boatís shine is gone and you canít get it back. Itís in a more extreme stage when you run your hand along the hull and a chalky substance is left on your fingers. For detailed information on how to restore your boatís finish, check out Don Caseyís article here on SailNet entitled Recovering the Shine.

Even when your boat is at anchor you can still access the topsides and give them the attention they need via dinghy.

In keeping our own boat protected, we prefer the liquid type of wax or polish as the application is easier than that of a heavy paste wax. We employ a paste wax when we need to remove dried varnish or paint from smooth gelcoat surfaces. Before scraping away the dried paint or varnish with a flat bladed window scraper, we first rub a little wax into the area to assist the blade in sliding smoothly over the surface and prevent digging into and nicking the gelcoat.

Boat Names and Graphics    Boat names that have been painted on your fiberglass hull can be removed by first applying oven cleaner, letting it sit for 15 minutes, and then wiping it away. To help remove evidence of discoloration between the hull and where the name was, use 3M Heavy Duty Rubbing Compound and lots of elbow grease. Vinyl adhesive names or graphics are sometimes impossible to just peel off, especially after they have been baked in the sun for years. To speed up the removal process, try heating the vinyl with a heat gun and use a flat scraper blade to coax it off the surface. Goo Gone or simple turpentine will help dissolve the adhesive still on the hull after the vinyl has been taken away.

The key to keeping your decks and topsides looking nice is regular cleaning, but it helps to have a few tricks up your sleeve. Hereís hoping weíve eliminated some of the trial and error for you regarding which products work and which donít. As for the elbow grease, well, youíll have to supply your own. Good luck.

Serengetti's Fiberglass Cleaning Kit

It doesnít take a lot of effort to keep the fiberglass on your boat in great condition, but for some reason itís easy for us all to let appearances slide. The worse it gets, the more we put it off because itís going to be such a big job. To help you stay on track with the not so difficult burden of fiberglass maintenance, you should assemble in advance a handy bucket of useful cleaning items. Make it a part of your regular boat routine to crank up some tunes and make that baby shine! Itíll only take a few minutes and your boat will love you for it! Hereís what we keep in our bucket:

  • Boat Soap
  • FSR or Y-10
  • Bar Keeperís Friend
  • Soft bristled scrub brush
  • Nylon scrub pad
  • Cotton rag
  • Bronze wool
  • Tooth brush
  • Small bottle of bleach
  • Plastic spray bottle
  • Liquid polish
  • Wax
  • Window paint scraper

  • Suggested Reading:

    Reducing Exterior Maintenance by Sue & Larry

    A New Shine for an Old Hull by Don Casey

    Cleaners, Polishes, & Coatings


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