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How To Whiten A Yellowed Fiberglass Bathtub: 9 Ways

Fiberglass tubs are lightweight and affordable, commonly used in many homes. Over time, soap scum and mineral deposits from the water can turn surfaces a dingy yellow.

You can easily clean a fiberglass bathtub with DIY methods and commercial products. Effective cleaners include baking soda and vinegar, dish detergent, and oxalic acid. In case of extensive damage, you may have to use a refinishing paint kit or replace the bathtub.

Determine If You Have A Fiberglass Bathtub

Acrylic, ABS, metal, porcelain, and fiberglass tub surfaces can all change color over time. While many of the methods in this article can work on all kinds of tubs, others don’t. 

Acrylic and fiberglass have similar characteristics and can be cleaned similarly. They both have some “give” when you push on the sides, and can suffer from scratches and cracks. 

If the bottom of the tub is faded more than the walls, it is likely a fiberglass one. Fiberglass will also have a finish that looks glassy. 

If there are chips, rust, or a magnet will stick to it, then it is most likely a metal tub, which could be coated in enamel. Metal tubs typically have additional supports in the underlying frame or bottom, since they are considerably heavier

Porcelain tubs will also chip and you will not be able to press in on the sides.

9 Ways To Whiten A Fiberglass Bathtub (With Alternatives)

When cleaning a fiberglass tub, you mustn’t use abrasive cleaning solutions or tools. You could scratch or further damage the surface. 

While small scratches can be remedied with a finishing kit, it creates the need for more money, time, and effort on your part.

These methods will also work well on textured tub surfaces if you apply a little scrubbing action with a soft toothbrush or bristle brush.

If you use more than one method, take care not to mix chemicals. Even natural ones mixed together could create toxic fumes or damage your tub. Before using a different method, make sure you have fully rinsed the tub with clean water and allowed it to thoroughly dry.

General Materials And Tools To Use

  • Spray bottle(s)
  • Bowl(s) for mixing
  • Microfiber cloths or paper towels
  • Soft bristle brush or non-abrasive sponge
  • Soft toothbrush
  • Cup or pitcher

Before Starting

  • Remove all toys, soap containers, and other items from the tub. 
  • Lay towels down to collect any spilled products and prevent slips.
  • Wear rubber gloves to protect your skin.
  • Use hot tap water as indicated in the methods below. This will help to loosen any debris on the surfaces.
    • Alternatively, you can steam the work area for 15 minutes by running hot water from the shower. 

1. Baking Soda And Vinegar

Baking soda is a gentle mildly abrasive component that can effectively remove stains and grime. Vinegar’s acidic properties will disinfect and remove hard water deposits.

What To Do

  1. Dampen all surfaces of the tub with hot tap water.
  2. Sprinkle baking soda onto the damp surfaces.
  3. Mix equal parts of water and vinegar in a spray bottle.
  4. Spray the baking soda-covered spots to create a fizzy reaction.
  5. Using a cloth, scrub the surfaces in a circular motion. Use a toothbrush to target any small spots or crevices.
  6. Let it sit for a minimum of 30 minutes.
  7. Scrub again with a new cloth, in circular motions.
    • For stubborn stains, cover the baking soda surface with a towel. 
    • Soak the towel with vinegar and let it sit on the spot for 60 minutes. 
    • Scrub the stains thoroughly.
  8. Use water from the faucet to fill a cup or pitcher, and rinse the tub clean.
  9. Repeat as needed.

Alternatives For This Method

This cleaning option can be modified using other ingredients commonly found at home.

Vinegar Substitutes

Instead of vinegar, you can use 3% hydrogen peroxide or lemon juice. These both are effective non-bleach acids to help whiten a fiberglass tub. Hydrogen peroxide should not be used on colored fiberglass, since it can fade colors.

Baking Soda Substitutes

Use salt, cream of tartar, or toothpaste (not gel or whitening) to scrub onto surfaces in conjunction with an acidic cleaner.

Add Dish Detergent

Add a generous squirt of dish detergent to your spray bottle. Dish detergent has surfactants that can help to wash away oils and other grime.

2. Borax And Lemons

Borax is commonly used as a laundry additive for removing stains and deposits. It can also remove mold and mildew and eliminates odor. 

Lemons sliced in half can provide an acidic scrubber to use in conjunction with a borax paste.

What To Do

  1. Dampen all surfaces of the tub with hot tap water.
  2. Sprinkle borax onto the surfaces.
  3. Cut a lemon or two in halves. Remove any seeds.
  4. Scrub the surfaces with the open face of the lemon in circular motions.
  5. Let the mixture sit for 1 to 2 hours.
  6. Rinse clean with water.

In place of lemons, you can also use hydrogen peroxide or vinegar in a spray bottle, with a soft scrubbing tool. 

Note: Borax converts into hydrogen peroxide when mixed with water. Hydrogen peroxide should only be used on white tubs since it can fade colored fiberglass.

3. Calcium-Lime-Rust (CLR) Remover

CLR is generally safe for use on fiberglass surfaces. However, since it is a commercial product it is best to test it in an inconspicuous spot first.

What To Do

  1. Spray the product onto the surfaces.
  2. Wear gloves and scrub as you spray with a soft bristle brush.
  3. Allow it to sit for 1 to 2 minutes, or as per the product’s instructions.
  4. Rinse clean with water.

4. Oxalic Acid

Oxalic acid can be found in commercial products such as Bar Keeper’s Friend in powdered or liquid form. This natural acid will eliminate mineral stains and is popularly used on fiberglass. Follow the product instructions for its use, using a soft scrubbing tool.

5. Tub And Tile Cleaners

Many commercial products will have a label that indicates it is for tub and tile cleaning. Refer to the labeling to ensure it is safe for use on fiberglass.

Other products, such as Soft Scrub, come with labeling that indicates usage on tubs and tile. However, there is bleach in some of these products, and they are abrasive. 

Test in an inconspicuous spot first to make sure it does not change the color, create scratches, or wear away any finish.

6. Vehicle Degreaser

Cars and trucks also use fiberglass, and a vehicle degreaser will remove oily residue from their surfaces.

Check purchased products for their use on fiberglass, test them in an inconspicuous area, then apply them to your tub following instructions.

7. Melamine Foam

Melamine foam used to make the product Magic Eraser, is mildly abrasive, especially if applied with force. 

This product will remove stains on fiberglass, but is generally reserved for spot or quick cleaning with a light touch. 

It should not be used regularly since it may wear down the finish or cause scratches. 

8. Ammonia

Ammonia can remove hard water stains. However, this can release toxic fumes and should be used in well-ventilated areas. Do not mix ammonia with other cleaning materials.

Wear gloves and apply equal parts of ammonia and water to the stained areas. Wipe down with a soft sponge and rinse clean.

9. Repaint And Refinish The Tub

Stains may persist if the finish of the tub is damaged, allowing mineral deposits and more to settle more deeply into the surface.

If you do not wish to completely replace the bathtub, repainting and refinishing are a last resort for removing discoloration.

Epoxy finishing kits can be purchased for use with fiberglass. Check the product’s label to make sure it can be used on your fiberglass tub.

The kit will include detailed instructions on what to do, including the ideal temperatures and humidity levels for application.

Generally, you will:

  1. Clean the surface
  2. Repair any cracks with compound
  3. Use fine-grit sandpaper to sand and smooth out patches
  4. Wash away any grit and debris
  5. Thoroughly dry the surfaces
  6. Apply the epoxy finishing paint, and allow it to dry
  7. Add a second coat of paint, and allow it to dry again

If you find the finish did not work correctly, it is usually due to improper conditions or applications such as:

  • Unclean surface
  • Unsanded surface
  • Residue buildup
  • The finishing paint application is too thick
  • The product was not shaken or stirred before use
  • The temperature and humidity were too high

 Alternatively, a professional tub installer can refinish the tub for you.

Maintenance And Prevention

Using the methods above, clean the tub once or twice a week.

Prevention Tips

  • Never use abrasive tools, such as steel wool or razor blades, and make sure to rinse all cleaning solutions away.
  • Do not use bleach on your fiberglass tub, since it can cause permanent yellowing that cannot be removed. If this occurs, the tub should be refinished or replaced.
  • If you are tempted to use turpentine, paint thinner, or acetone, think twice! While these may remove stains, they can cause scratching or etching with repeated use. These are considered hazardous and illegal to empty into water sources in many places.
  • You should thoroughly dry fiberglass surfaces after every use to avoid buildup with a soft towel. Additionally, you can turn on your bathroom fan, use a dehumidifier, or open a window after bathing to shorten the drying time.

Key Takeaways

In most cases, yellow fiberglass tubs are easy to clean on your own. Use DIY cleaners such as baking soda and vinegar or commercial products formulated for tile and tub cleaning or degreasing fiberglass surfaces. 

Scratched fiberglass bathtubs may need finishing paint to make them look like new again, using a kit from a home improvement store. 

Weekly cleaning and maintenance can prevent buildup and yellow stains in your tub.