Water Stain and Mildew Removal

If you experience condensation on the exterior or interior of your window and door surfaces, you may notice discoloration along the lower parts of your wood windows or doors. This discoloration is likely the result of mildew or water stains. Mildew is a fungus that thrives on warmth and moisture, but can flourish to some extent under all climatic conditions. Mildew growth is usually brown or black in color, and for this reason, may be mistaken for dirt. Follow the instructions below to care and maintain your Marvin products.


If you experience quite a bit of interior condensation, you may notice discoloration along the lower parts of your wood windows or doors. This is the result of mildew growing in damp areas. Use regular laundry bleach on a sponge to remove the mildew.

Please note: The application of a bleach and water mixture is likely to discolor and/or remove the interior wood finish and sealant. It will be necessary to refinish the wood after bleaching.

  • 1. Wear protective eyewear and skin protection, and keep the area well ventilated.
    2. Mix one cup of regular laundry bleach to one gallon of water.
    3. Dampen sponge.
    4. Stroke lightly on the affected surface. Do not rub.
    5. Make sure the grain of the wood is penetrated and reapply bleach-and-water mixture if the discoloration persists.
    6. After bleaching, refinish the wood to match the rest of your window or door.


The presence of mildew on your exterior can be confirmed by placing a drop of household bleach on the suspected mildew area. If small gas bubbles develop in the droplet of bleach and the area bleaches out, mildew does exist and should be removed from the exterior of your windows or doors.

Use this basic solution for controlling exterior mildew.

  • 1. 1/3 cup powder laundry detergent
    2. 2/3 cup trisodium phosphate (TSP)
    3. 1 quart household bleach
    4. 3 quarts water

Please note: A stronger concentration of cleaner can damage the coating surface or finish.

Always wear protective eyewear and skin protection when using harsh cleaning compounds.

Apply the solution with a soft bristle brush using medium pressure.

Rinse the finish well with clear water after cleaning.


Oxalic acid can be used to bleach bare, unfinished wood that has been water stained.

Oxalic acid is a poisonous strong organic acid used especially as a bleaching or cleaning agent. It can be purchased at hardware, drug, or grocery outlets.

Always use eye and hand protection and read the manufacturer’s instructions and application procedures carefully before using.

Application procedures:

  • 1. Mix approximately 2 tablespoons of oxalic acid to 8 ounces of water in a pan.
    2. Dampen sponge.
    3. Stroke lightly on affected surface.
    4. If the affected area is not completely bleached in the first application, let the area dry completely and then reapply the acid.


Condensation is visible evidence of excessive moisture in the air. It may appear as water, frost, or ice on the interior surface of windows or doors. If you experience quite a bit of condensation, you may notice discoloration, or mildew, along the lower parts of your windows or doors.

Condensation may be the result of one of three occurrences:

  • New Construction or Remodeling
    Humid Summers
    Temperature Changes

Windows and doors do not cause condensation. Therefore, windows and doors can not cure condensation. To learn more about condensation and how to control the humidity level in your home, view our Condensation FAQ.


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