Removing Mold from Wood

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Wood is a hygroscopic material, which is a fancy term that means it likes to soak up and retain water (think of a sponge).  This makes sense, since wood comes from trees, which soak up water to grow.  While this is good for the tree, its not good for your lumber, furniture, or trim. Let’s go through the steps and talk about some specific issues when removing mold from wood.  Keep in mind these steps assume the mold covers a relatively small area (i.e. less than 10 square feet).

Step 1- Choose a cleaning solution

There are many commercial products that are pre-mixed to tackle mold problems. To remove mold from wood, make sure the cleaning solution fits the situation. For example, if you are trying to remove mold from wood that is finished or painted, you can rely on more mild cleaning solutions because you don’t have to kill the mold, you can just remove it. If the mold is established below the surface of the wood, which often happens on unfinished wood, you will need a solution that will penetrate the surface and kill or inhibit the mold.  Here is a list of suggested solutions to choose from depending on the situation:

Remove mold from wood – finished or painted wood:

  • Mixture of household detergent and water
  • Commercial mold removal product (always follow manufacturer’s instructions on the label)
  • Distilled Vinegar
  • Baking Soda -Detergent Solution (1/2 cup baking soda, 1 cup water, 1 Tbsp mild liquid detergent)
  • Borax Solution (1 gallon of water to 1 cup of borax, or 1 part borax to 16 parts water)

Remove mold from wood – unfinished wood:

  • Rubbing Alcohol or Denatured Alcohol
  • Commercial mold removal product (always follow manufacturer’s instructions on the label)
  • Distilled Vinegar
  • Borax Solution (1 gallon of water to 1 cup of borax, or 1 part borax to 16 parts water)
  • Baking Soda -Detergent Solution (1/2 cup baking soda, 1 cup water, 1 Tbsp mild liquid detergent)
  • Bleach-Detergent Solution (Recommended by the US Forest Products Labratory – 1 part household detergent, 10 parts bleach, and 20 parts water)

Warning: Never mix bleach with a product that contains ammonia.  It will produce toxic fumes that can cause serious illness or death.

 

Special note on Bleach:

When working with wood, you should be aware that bleach can only kill mold spores that are on the surface of the wood.  Mold in wood, however, tends to grow and establish roots below the surface and into the wood fibers.  Due to the chemical makeup of bleach, it does not absorb into the wood, and it is possible that you will see the mold re-establish itself after you have cleaned it with bleach.

To address this problem, several companies have produced mold removal products that include surfactants.  What the heck is a surfactant you ask?  To put it simply, a surfactant is an additive that allows the detergent or bleach to absorb deep into the wood fibers.  It does this by reducing the water surface tension, but that is something for another discussion. The detergent in the suggested mixture above helps to allow the bleach to get down to the roots of the mold.

So, the bottom line is you can elect to use bleach, but keep in mind that there are better products to remove mold from wood.  If using a commercial product, look for an EPA registered mold removal product (regular household bleach does not have such claim).

 

Step 2 – Put on Protective Clothing and Make Safety Precautions

Depending on the severity of the cleaning solution that you chose, you will need to take some safety measures in order to keep yourself free from harm.  Before you try to remove mold from wood, we recommend the following:

  • A respirator, or air mask, that is adequate for blocking mold spores from entering your lungs.  The EPA recommends a N95 mask or equivalent.
  • Rubber or Nitrile gloves.
  • Safety goggles that do not have air vents in the sides.
  • If you are moderately sensitive to mold exposure, we recommend wearing coveralls to protect your skin as much as possible.  If you are severely sensitive to mold exposure, we recommend getting somebody else to perform the task.

If you are using a product that has strong or dangerous fumes, also make sure your are working in a well ventilated room.

 

Step 3 – Apply the Cleaning Solution and Scrub

Apply the cleaning solution that you have elected to use.  Start by testing the solution in a small, hidden area of the wood to make sure the solution does not cause any discoloring.  You can do this with a spray bottle, a lightly damp rag, low-abrasive brush, or a scrub pad.  If you are working on finished or painted wood, we do not recommend using a brush unless you plan on re-finishing the surface.

The key is to apply the solution lightly, but enough to cover the mold.  Too much solution can actually add to the dampness of the wood, which is part of the problem in the first place.

Let the solution sit for a few minutes, then scrub the area in circular motion with your rag, brush, or a scrub pad.  Using a disposable towel, or a towel you can disinfect with bleach later, wipe of the area and the excess.

Continue this process until the mold is removed from the wood surface.

Step 4 – If Needed, Lightly Sand the area

If you are working with finished wood, then this step will require you to re-finish the area that you are sanding.

If the mold appears to be established deeper into the wood, you will likely need to lightly sand the area.  This helps to remove the mold roots on the surface, and gets you deeper into the wood fibers.  You should sand the area while it is still damp to discourage mold spores from spreading through the air.

After sanding, repeat step 3.

 

Step 5 – Clean Up and Let Dry

After you remove mold from wood, clean up the area and either dispose anything that has had contact with the mold, or clean it with a proper detergent or fungicide.

Let the wood dry by keeping in a warm, dry, sunny area with good ventilation.  If you live in an area with higher humidity, you may want to place it in a room with a dehumidifier.  Leave it until the wood looks and feels dry.

 

Step 6 – Check for Signs of Mold

After the wood has dried,  look to see if there is still mold and if the area smells moldy.  Sometimes the wood will be stained from the mold even though the mold is gone.

If the mold is still visible or the odor is still strong, repeat this process again.

 

Step 7 – If Needed, Re-apply Protective Wood Coating

If you have scrubbed or sanded finished wood, you will probably need to re-apply the polyurethane, lacquer, protective stain, or whatever finishing product that was on it.

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