How to clean yellowed fiberglass

Updated February 21, 2017

Fibreglass surfaces, such as bathtubs or boat hulls, may form yellow stains over time due to minerals and dirt in water. The yellowing dulls the fibreglass, leaving the once white and gleaming surface looking dingy and worn. Fibreglass requires a robust cleaner that removes the yellow stains without etching the surface. Fortunately, household items from your kitchen remove the discolouration and restore shine to the fibreglass top.

Pour 1/4 cup cream of tartar into a bowl. Add 1/2 tsp hydrogen peroxide to the bowl and stir. Continue adding the hydrogen peroxide by 1/2 teaspoonful until the cream of tartar is a thick consistency.

Place a small amount of the cleaning solution onto a damp sponge. Wipe the sponge over the yellowed areas of the fibreglass. Place additional cleaning solution onto the sponge as needed. Cover the stains completely with the cream of tartar. Allow the solution to remain on the fibreglass for two hours or until dry.

Wet a sponge with warm water. Wipe the sponge over the fibreglass, removing the cream of tartar. Rinse the fibreglass surface entirely and dry with a clean cloth.

Mix 1/2 cup baking soda with enough warm water to create a thick paste.

Wet the fibreglass by wiping it with a wet sponge. Place the baking soda paste onto the sponge and wipe over the yellowed areas on the fibreglass. Use medium pressure as you scrub the stains.

Rinse the fibreglass with water. If portions of the stains remain, repeat the cleaning process with the baking soda.

Rinse the fibreglass with a wet sponge after removing the stains, and dry with a clean cloth.


Avoid using an abrasive tool such as steel wool on fibreglass, as it may etch the surface.

Things You'll Need

  • Cream of tartar
  • Bowl
  • Hydrogen peroxide
  • Sponge
  • Cloth
  • Baking soda
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About the Author

Constance Barker, located in the hills of southern Ohio, is the owner and writer of several financial, credit report and travel websites. She started writing in 1999 for private clients and began creating website content in 2004. She gained expertise in home improvement after she and her husband built their home themselves.