Tips for Cleaning a Fiberglass Boat

Fiberglass is a great structural material for building boats, and is usually made with a special outer surface resin called gelcoat. This resin protects the fiberglass boat’s hull and gives it a smooth, reflective color and shine. However, as fiberglass boats age, the gelcoat gets dull, gloomy and chalky. 

Fiberglass boat cleaning tips

It also becomes porous, stains more easily, and becomes a lot harder to clean. Some boat owners may come to accept the aged, weathered exterior of their fiberglass boats over time. However, if it ever comes time to sell your boat, who’s going to buy it if it looks like it was never cared for? Cleaning and maintaining a fiberglass boat and its gelcoat surface helps maintain a good resale value. Here are some tips for cleaning and caring for a fiberglass boat. 

Buy marine fiberglass repair products

Buy gelcoat repair products

Handling Fiberglass Gelcoat Stains

Sometimes a little soap and water is all it takes to remove fiberglass boat stains. However, there are two main types of stains found on fiberglass boats that can’t always be removed with ordinary soap and water: mineral and organic. 

Fiberglass boat hull washing

Organic stains are discoloration caused by matter such as bird droppings, aquatic plant-or-animal secretions, and spilled food and drinks. A wide variety of fiberglass stain removers are available to remove organic stains such as mildew, or mineral stains such as rust. Trying to remove a mineral stain like rust with only soap and water is a lost cause, and will require a special rust stain remover to do the job. 

Fiberglass boat cleaning organic stains

Waterline stains, which can be made of both mineral and organic substances, are another type of common stain that requires specially formulated cleaning products to remove. Regardless of the stain type, the important thing to keep in mind when selecting fiberglass boat cleaning products is to avoid using any harsh chemicals that could damage the delicate gelcoat surface of your boat. Whether you’re ready to restore your boat’s fiberglass finish or just want to give it some TLC, follow these steps for how to clean your fiberglass boat:

Fiberglass boat hull stain cleaning

Step 1: Wash your Fiberglass Boat

If you want your fiberglass boat to regain some of its lost luster, a simple soap and water wash is the easiest first step to follow. Rinse off your boat with warm, clean fresh water. Use a specialized boat cleaning soap, and follow the instructions for mixing amounts into a bucket of water. 

Fiberglass boat washing

Once the soap and water are mixed, wash your boat’s gelcoat surface with a long-handled soft brush or sponge, and rinse it off again thoroughly with fresh water to remove any excess grime, dust and debris. Dry your boat off with towels to prevent moisture buildup, which can lead to mildew growth. If mildew stains are present on your boat, apply a specialized mildew stain remover to get rid of them. 

Buy boat cleaning supplies

Buy mold and mildew removers

Step 2: Degrease your Fiberglass Boat

Soap and water alone won’t remove oil and grease, so the next step after washing your boat is to degrease it. Degreasing helps protect and restore gelcoat, and should always be included as part of your boat cleaning routine. 

Fiberglass boat cleaning degrease

Don’t skip this step to save time, as the gelcoat needs to be free of oil and grease before moving on to polishing and waxing. Apply a non-scratching degreasing formula over the surface of your fiberglass gelcoat using a damp cloth, then rub it off with a microfiber towel, or use a quality spray-on-and-rinse-off degreaser product instead. Once you’ve properly washed and degreased your fiberglass boat, make sure you let it dry before moving on to the next step. 

Step 3: Polish your Fiberglass Boat 

The next step after washing and degreasing your fiberglass boat is to polish it. Polish is not a coating like wax, but rather an abrasive substance that smooths out a pitted gelcoat surface. 

Fiberglass boat cleaning polish wax

Apply a high gloss polish onto a soft cloth or a damp foam polishing pad, and rub it in a circular motion into small areas at a time. You can polish the gelcoat surface by hand if your boat is small enough, but your arm will tire out very quickly on larger boats. Use a low-speed circular electric buffer with compounding and buffing pads for larger vessels to save some time and elbow pain. When you’re done polishing the gelcoat, use a microfiber towel to wipe down your boat.

Fiberglass boat cleaning waterline stains

If the gelcoat surface of your boat is heavily weathered or oxidized, polishing may not be enough to restore it, and a rubbing compound might be needed instead. Before selecting a boat polish or a rubbing compound, keep in mind that these are abrasive products designed to smooth the pitted surface of a porous gelcoat and restore its shine. These products might wear down some of the gelcoat with each use, so make sure you choose less abrasive products. 

3M Marine rubbing compound

Buy boat wax

When choosing a rubbing compound, make sure it’s formulated specifically for fiberglass use, and apply it using a circular hand motion or an electric buffer. If you’re using a circular electric buffer, use gentle pressure and keep the machine mobile, as pressing too hard and focusing too long on one particular spot can damage the gelcoat. 

Step 4: Wax your Fiberglass Boat 

The next step to restoring your fiberglass boat’s gelcoat is to apply a coat of wax, which provides a protective coating and improves its gloss. Waxing is not a step you want to ignore, unless you want the gelcoat exposed to sun and water damage, and other gelcoat killers. 

Fiberglass boat cleaning tips waxing

Application instructions vary depending on which product you select, but the same technique used for applying the polish or rubbing compound can be used to wax your fiberglass boat. Allow the wax to dry off until it has a hazy appearance, then use a soft cloth to wipe away the excess residue for a smooth, reflective surface. 

Color Restoration

More of an alternative to waxing, color restoration isn’t a necessary step, but there are products available to restore the gelcoat surface without the need for wiping or electric buffing.

Fiberglass boat cleaning tips color restoration

If you decide to go with a color restorer instead of a wax, make sure you select one that won’t scratch or damage the gelcoat. Restorers are a plastic or acrylic coating known to flake off over time, so applying multiple coats is recommended with each treatment. Five coats of color restorer are typically recommended once every year, and you should remove the previous year's color restorer treatment with a stripper before applying a new treatment. 

Fiberglass Boat Cleaning Safety

Before starting the cleaning process of your fiberglass boat, make sure you use gloves to protect your hands, as well as safety goggles and protective gear for your skin. Kneepads are also highly recommended.

Fiberglass boat cleaning tips safety

Always read the labels on any cleaning product to find out what it’s made of and what types of stains it’s formulated to combat, and follow the instructions on how to use it. Make sure your fiberglass boat is in a well-ventilated area before using chemicals such as polish, rubbing compounds and restorers. Set aside a significant block of time to avoid cutting corners, skipping steps or missing spots. The better you care for your boat’s fiberglass surface, the longer you can go without having to repeat this process. Regular soap-and-water washes after following the steps provided above will help ensure the gelcoat lasts longer, and that the entire cleaning process doesn't have to be repeated as often.

Fiberglass boat cleaning tips finish

Once you’re done cleaning, polishing and waxing your boat, take it out for a ride and show it off! Isn't that part of the fun of owning a fiberglass boat with a gelcoat finish?