How To Remove Rust Stains From A Fiberglass Boat ( 5 Easy Steps)

Rust stains on boats are unsightly and can detract from the beauty of your vessel. If left untreated, rust stains can eventually cause permanent damage to your boat’s gel coat or paint finish.

How To Remove Rust Stains From A Fiberglass Boat. There are a few simple steps you can take to remove rust stains from your fiberglass boat.

How To Remove Rust Stains From a Fiberglass Boat

A boat can be used in fresh or saltwater. It is essential to clean the hull after use in either saltwater or regular tap water containing dissolved minerals.

When these minerals remain on the hull, they will mineralize and become rigid, making them difficult to remove later.

These calcium deposits are called “coral” and take time to build upon the surface of the fiberglass.
Rust is the result of iron and oxygen combining in water, which causes it to form a chemical called ferric oxide.

As this chemical builds up on your surface, you may notice that it starts taking on an orange or brown coloration from oxidation.

The presence of moisture also speeds up the process by increasing the rate of oxygen reacting with iron particles suspended in water to form more ferric oxide deposits.

In order to get rid of these nasty rust stains, there are several steps you can take.

Steps Involved

The following procedure may be used for removing rust stains from your fiberglass boat:

Step One

Begin by wetting the surface to submerge it in the water safely. Using a scrub brush, scrub the rust stains with an abrasive pad or brush that will not damage the surface of your boat.

Use hot water for stubborn spots, and then rinse thoroughly with clean water. You can use an old toothbrush to get into hard-to-reach areas.

Rinse again with clean water to remove any residual soap residue, which may cause corrosion issues later on.

Step Two

Use a household preparation called “Iron Out,” specifically designed to clean up rusty metal surfaces and remove rust stains from fiberglass boats. Iron Out, comes in two forms:

Liquid and Gel. Both are equally effective pick which you prefer. First, apply to the rust spots with a scrub brush.

Allow this solution to sit for several minutes, and then rinse thoroughly with clean water.

Step Three

Make your cleaning solution by adding one tablespoon of dishwashing liquid or laundry soap to five gallons of hot water.

Then, scrub the surface again using this homemade solution and allow it to soak for at least 30 minutes before rinsing off with clean water.

Step Four

After rinsing away all traces of the cleaning products, you may use an acid-based gel called CRC Marine.

Which will eat any remaining rust stains on your boat’s hull to produce a squeaky clean shine that will last well into boating season.

Put on gloves and goggles to protect your hands and face. Put a small amount of the gel onto a bristle brush, then liberally apply it all over the hull.

Please don’t be stingy with this stuff you’re applying acid, so use it generously. Let the gel sit for 30 minutes before rinsing it away with clean water underneath will be spotless nautical pride.

Step Five

To prevent rust stains from accumulating on your fiberglass boat in the future, coat the whole hull surface (including the deck) with an anti-fouling paint such as “CRC Marine Teak Bright”.

Or other nonabrasive wax designed especially for boat finishes. Reapply every couple of months for maximum anti-fouling protection.

How Do You Remove Brown Stains From Fiberglass Boat

Many things can cause brown stains on a boat. However, three prevalent types of stains occur on fiberglass boats.

One is caused by the drying out of old oil residue that was once part of the boat’s bilge system. Another is caused by dirt, mold, or mildew that was not cleaned regularly.

Lastly, brown stains can come from algae growth. Algae are the result of either too much water on the boat’s surface, or it can be the result of not having enough sunlight.

To remove brown stains from fiberglass, you can use Clorox; I recommend Fels-Naptha or Barkeeper’s Friend. Both of these chemicals are either acidic (Clorox) or slightly alkaline (BKF).

I would recommend using the Fels-Naptha because it is readily available. To remove stains, use a soft bristle brush and a paste of soap.

You can choose to rinse the boat off with fresh water. Instead, this is not required. You can use either soap or water to remove the stains.

The choice is yours. After you have done this, you should dry the boat’s surface with a terry cloth towel.

If you are not going to polish your fiberglass boat, allow it to dry for several hours before transporting the boat.

What is the Best Thing to Clean a Fiberglass Boat With

Fiberglass boats can be a dime a dozen. They come in different colors and sizes; some people even have them in their homes, where they use them as a pool or patio.

However, these fiberglass boats are not something you want to take lightly because if they get too dirty, your summertime will be spent cleaning them rather than enjoying it.

There are many different ways to clean fiberglass, but mixing water and baking soda is the best way.

The water acts as a solvent for the baking soda while gently exfoliating off all of the dirt and grime accumulated on your boat.

The advantage of this method is that it will not scratch or dull your boat’s exterior. This method is excellent because the baking soda will melt and get rid of all of the stains on your boat.

However, if you want to double up on cleaning power, you can also add lemon juice to your mixture.

Lemon juice has a natural bleaching property that will get rid of any dirt or stains deeply embedded in the fiberglass.

Do not forget that there are also many different products available for purchase. Each one is made to do a specific job.

So be sure to read the labels before you go out and buy them. So if your fiberglass boat has seen better days, then now’s the chance to bring it back to life with some cleaning methods.

Will CLR Remove Rust From The Fiberglass Boat

Yes, CLR will remove rust from fiberglass. However, you need to make sure your boat is clean and dry before using the product.

For CLR to work correctly there can be no residue on any part of the boat that would prevent good contact between it and the product.

If your ship is not completely dry from all the previous attempts to remove rust from it, this will be a waste of time and money because CLR will not work.

You also need to make sure that there are no oils or other residues on the fiberglass part of your boat before applying CLR to the metal part.

These oils can interfere with CLR’s ability to do its job correctly. When you have cleaned the metal part thoroughly and removed all residues from oil, dirt & rust.

You can take a clean cloth and apply a thick coating of CLR directly onto the metal part of your fiberglass boat.

The thick coating helps prevent any surface damage to your fiberglass and makes good contact with the cleaner rust so that it can do its job without unnecessary harm to your fiberglass boat.

Wait for the CLR and rust residue to dry completely before rinsing the metal part of your boat with a hose. Then you can try buffing off any remaining rust from the metal that CLR cleaned.

You can also use a cloth or brush for this purpose and sandpaper if there is stubborn rust that would not come up with just water and some cleaning using a nonabrasive pad on your buffer machine.

How Do You Remove Yellow Stains From Fiberglass Boat

Fiberglass boats often accumulate yellow stains at the waterline that are difficult to remove. It is because minerals usually cause stains in water that react with sunlight. To remove yellow stains from fiberglass boats:

1. Scrub the stain with a mixture of 3 parts vinegar to 1 part water.

2. If the stain persists, try a mixture of 1 part bleach to 4 parts water.

3. If you cannot remove the stain with these solutions or discolor the gel coat, add 1 tablespoon of powdered laundry detergent to 4 tablespoons of household ammonia in 2 quarts of warm water.

After scrubbing the stain with a mild abrasive, Rinse the boat thoroughly. For difficult stains on whitewalls, brush a solution of 50% bleach and 50% water onto the color.

Rinse the whitewall thoroughly, as well as any surrounding surfaces, to avoid bleaching. Prevention is the most effective way to limit yellow stains on your fiberglass boat.

Saltwater causes most Gelcoat staining, so determine boating in brackish and saltwater. If your boat is stored in the water, flush it before using it for the season.

Then, use a long-handled brush to scrub the waterline, rinse with fresh water and dry carefully.


If you’ve been wondering how to clean your fiberglass boat, we hope this guide has helped. You can use several different solutions and techniques depending on the type of stain or dirt.

For example, using CLR may work well with rust stains but not with yellow ones. We also recommend checking out our blog post about removing brown stains from boats.

Which contains additional information and tips on cleaning various types of materials found in vessels such as vinyl flooring, carpeting, or wood panels.

Again, we hope that the information in this article has helped you.

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