DIY iconDo-it-Yourself: Maintaining Your Boat’s Gelcoat Finish

By Brian Gordon, Last updated: 7/16//2018

Pride of Ownership

Family washing PWC

Owner apathy and the state of a boat’s gelcoat go hand in hand. Many owners blithely accept the chalky drab exterior of their boats as a fact of life. After all, bright and shiny gelcoat doesn’t make a boat sail any better or catch more fish, so why bother with maintenance? But keep in mind that a great looking boat will help you “catch” more customers when the time comes to sell your boat. And, like a clean car, a clean boat just seems to “run better.” So now is the time to breathe new life in to your boat’s gelcoat!

Gelcoat is the coating sprayed up against a highly polished mold at the beginning of the fiberglass layup process. On new boats, this surface is very smooth, mirror-like and pleasing to the eye. As gelcoat ages, it becomes porous. The more porous it becomes, the more easily it stains, the worse it looks and the harder it is to clean. The good news is that almost all gelcoat can be restored, providing it is not completely worn through.

Removing Gelcoat Stains

The best way to minimize gelcoat staining is to seal and protect it with a good quality wax or polish, then follow up with regular washdowns, using a gentle boat soap that will leave this protection intact. Unfortunately, despite our best efforts, gelcoat stains will eventually occur.

MaryKate's On & Off Hull & Bottom Cleaner is powerful stuff! A large number of our customers give it a perfect 5.0 rating.

Mineral and organic stains

Selection of a stain remover should be based on the type of stain you wish to remove. There are two types of gelcoat stains: mineral and organic. Organic stains include the discoloration that remains after removal of bird droppings, plant matter, and spilled food and drink, such as coffee and wine. Mineral stains include rust stains, which frequently occur around stanchion bases, chainplate covers and exhaust ports. Other common stains include waterline stains and “black streaks” (which are not always black) caused by minerals leaching out of dirt as it runs out of scuppers and flows down the hull. Gelcoat stains may be localized or cover the entire topsides and hull.

There are a wide variety of gelcoat stain removers, each of which is formulated to remove a specific type of stain. When removing a stain, the objective is to eliminate the stain without damaging the gelcoat itself. Avoid using strong solvents, such as MEK or acetone, and abrasives such as heavy rubbing compound or, worse, sandpaper.

Wash the area

To remove a gelcoat stain, begin by washing the affected area with soap and water. This alone will remove many stains, provided they are water-soluble. However, attempting to remove a mineral stain with soap and water is a waste of time, because these stains are not water-soluble. Mineral stains require products specifically formulated for their removal. These products usually contain an acid and/or a chelating (key-lay-ting) agent. Acids dissolve mineral stains while chelating agents chemically bond to the stain and hold it in suspension until it is rinsed away. All feature simple spray- or wipe-on application and, because they rely on a chemical reaction, little or no scrubbing is required.

Stain removing products

Products tailored to remove organic and mineral stains on deck and rust around hardware include FSR by Davis, West Marine Fiberglass Stain Remover, and Rust Stain Remover (Model 126823) by Star brite. FSR and Fiberglass Stain Remover are non-runny gel formulations, making them excellent for horizontal and vertical surfaces. Products such as West Marine Black Streak Remover and 3M’s Black Streak Remover (Model 3760212) are tailored to remove the “black streaks” described above. With their simple spray- or wipe-on application, little or no scrubbing is required.

Heavy stains

Heavy waterline stains and the scum and calcium growth encountered at haulout require a more aggressive approach. Products such as Mary Kate’s On & Off Hull/Bottom Cleaner and are strong acid formulations that really pack a punch. They are easily applied with a rag or brush and like other acid-based products simply require that you wait a few minutes before rinsing them off. Because of their caustic nature, rubber gloves and eye protection should be worn. 

Restoring gelcoat shine

Once the stain is removed, take the time to apply a protective coat of wax to the gelcoat. This will provide a barrier between staining materials and the pores in the gelcoat, making removal of future stains much easier. If your gelcoat still has a drab or chalky appearance after removing the stains, it is most likely suffering from oxidation—so it is time for you to restore its shine!

Tools for making gelcoat shine

Before beginning, assemble the right tools. You will need a medium to coarse deck brush, a separate soft-bristled brush, chamois and plenty of clean cotton rags. You will also need a pair of goggles to protect your eyes and, because you will be working on your knees, you will also need protective kneepads.

Rubbing a boat out by hand is a real work out, so to save time and ease the pain we also suggest you use an orbital or low speed circular electric buffer with a set of quality compounding bonnets. If you plan on polishing the boat while it is in the water, we suggest the buffer be of the non-corded rechargeable type, or the GFCI-protected Shurhold 3100, as water and electricity are a dangerous combination!

Clean and inspect the surface

Start the restoration process with a complete washdown using an aggressive cleaner-degreaser such as Pure Oceans Heavy-Duty Boat Soap. After rinsing, dry with a chamois and inspect for rust or mineral stains. To remove obvious staining or to brighten the topsides as a whole, try using Pure Oceans Fiberglass Stain Remover. Now is the time to inspect for scratches, dings, cracking and crazing and to fix these flaws before rubbing out the gelcoat and restoring its shine.

The Shurhold buffer is a quality product with a 500W motor and six speeds, and includes a GFCI outlet for safety.

Power buffing

Depending on the level of oxidation, polishing/compounding and waxing can be a one- or two-step process. Either can be done by hand or electric buffer, the latter being what we recommend. When using a power buffer, apply gentle pressure and always keep the machine moving. Pressing too hard or allowing the machine to remain on one spot for too long will result in “burn through” and possible gelcoat damage. Work small areas in a systematic manner and don’t move on until each area is done. Molded-in non-skid should not be polished, compounded or waxed. Instead, it should be simply washed/degreased and brightened per the stain removal procedure described above.


Before making a product selection, it is important to understand that polishes and rubbing compounds use abrasives to smooth the pitted surface of porous gelcoat and restore the shine. Each time these products are used, some of the gelcoat is removed. Care should be taken to use the least aggressive product that will get the job done. Frequently, where little or no oxidation exists, all that may be needed is to apply a protective coating of wax.

Cleaners, restorers and waxes

Whenever possible, we like to recommend liquid one-step products that combine a polish or compound with a wax-after all, why spend all day on a project when you can finish the job in half the time! Outstanding one-step products include NanoTec Fiberglass Cleaner Wax and 3M Restorer & Wax. These products remove oxidation, and protect the gelcoat in one easy step, so you can get on to better things like having fun on your boat! 

Where oxidation cannot be removed with a one-step product, a rubbing compound may be needed. In the case of very heavy oxidation, UltraCut Rubbing Compound will do the job. Once the oxidation has been removed and the shine restored, the gelcoat must be sealed and protected with a wax. Wax may be of the traditional carnauba wax variety, such as Pure Oceans NanoTec Paste Wax or a polymer formulation such as Meguiar’s Flagship Premium Wax.

Once you have finished the restoration, all you need to do is follow up with regular wash downs and periodically apply a fresh coat of wax. And oh yes, you can now kick back and start accepting the compliments!