How to Kill Mold on Pressure Treated Lumber

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Things You'll Need

  • Commercial exterior wood cleaner, powder form

  • Warm water

  • Bucket or spray bottle

  • Five-way tool

  • Sponge or rag

  • Fungicide

Stack of lumber
Image Credit: Hemera Technologies/ Images

As conditions permit, mold can grow on pressure treated lumber or wood. Conditions for cultivating mold include hot and moist temperatures. Heat can be generated from the weather or the sun shining in a well-insulated building, and moisture can come from the humidity or wet wood that has been piled up and not ventilated. Mold can be killed in numerous ways. One of the most popular ways to kill mold is bleach, but you cannot use bleach on pressure treated wood because you will cause damage to the wood.


Step 1

Locate all lumber that has mold.

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Step 2

Clean off any thick patches with the five-way tool. Be extremely gentle to the wood when using the five-way tool in order to avoid damaging the lumber. If the mold looks like stains, proceed to step 3.


Step 3

Mix the commercial exterior wood cleaner with correct amount of warm water in the bucket or spray bottle. Mixtures depend on your needs. If you have a lot of wood that needs treated, then more powder and water will be required.

Step 4

Spray the mixture on the treated lumber, and scrub gently with a sponge or rag until the marks are gone.


Step 5

Allow an hour or more to dry.

Step 6

Spray a wood safe fungicide on the areas where mold propagates.

Step 7

Allow to dry completely in the sun.


Use an organic fungicide to ensure no harm will come to the wood. Create conditions for your lumber that will not breed mold or mildew and possibly damage your lumber. Perform a splash test that will show you what kind of results the commercial cleaner will have on your lumber.



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