Chemically Clean a Wood Deck before Staining and Resealing

Last week, we took a pretty deep look into why it’s important to wet a deck surface before you apply a chemical cleaning agent to the deck. In simple terms, if these chemicals are applied to a dry deck, the chemical will soak too deep into the wood fiber and can cause long-term damage and or accelerated deterioration.  Today we’re looking at a similar related topic about preparation and cleaning and why it’s important to clean a wood deck before applying new coats of stain or sealers.

There are several different classifications or categories of cleaners that can be used to clean and prepare a wood deck.

• Oxygen Bleach Cleaners
• Chlorine Bleach Cleaners
• Oxalic Acid Cleaners
• Sodium Hydroxide (Lye) Cleaners
• Citric Acid Cleaners

A brief overview of these cleaners follows:

Oxygen Bleach Cleaners are environmentally friendly and safe for most wood types. They typically come in powder form and are activated when mixed with water. These cleaners are effective at removing mold, mildew, and algae without damaging the wood or surrounding vegetation. They’re often marketed as “eco-friendly” or “biodegradable” deck cleaners and can be found at retailers.

Chlorine Bleach Cleaners are strong and effective at killing mold and mildew, but they can be harsh on wood and surrounding plants. They’re usually diluted with water before application. While common household bleach can be used, there are also specialized chlorine-based deck cleaners available. These are sometimes labeled as “mold and mildew removers.”

Oxalic Acid Cleaners are particularly effective at removing rust stains and weathering from wood. They come in crystalline form and are mixed with water before use. These cleaners are often marketed as “wood brighteners” or “wood restorers”.

Sodium Hydroxide (Lye) Cleaners are powerful alkaline cleaners that can remove tough stains and strip old finishes from wood. They’re often used for heavily soiled decks or as part of a refinishing process. These cleaners are typically found in concentrated liquid form and must be handled with care due to their caustic nature. They’re often available from our professional / industrial-grade suppliers.

Citric Acid Cleaners are milder, more environmentally friendly alternatives to harsher chemicals. They’re effective at removing light stains and brightening wood. These cleaners often come in powder form to be mixed with water or as ready-to-use sprays. They’re frequently marketed as “natural” or “organic” cleaning solutions.

Some more of the technical details about each of these particular product classifications or categories:

1. Oxygen Bleach Cleaners:
   • Active ingredient: Sodium percarbonate
   • pH: Slightly alkaline (around 8-9)
   • Action: Releases oxygen ions in water, breaking down dirt and killing mold/mildew
   • Advantages: Eco-friendly, safe for plants, non-corrosive
   • Disadvantages: May not remove tough stains or gray weathered wood
2. Chlorine Bleach Cleaners:
   • Active ingredient: Sodium hypochlorite
   • pH: Highly alkaline (11-13)
   • Action: Strong oxidizer, kills mold/mildew, brightens wood
   • Advantages: Effective at removing mildew stains
   • Disadvantages: Can damage wood fibers, corrosive to fasteners, harmful to plants
3. Oxalic Acid Cleaners:
   • Active ingredient: Oxalic acid (H2C2O4)
   • pH: Acidic (1-2)
   • Action: Removes rust stains and tannin bleed, brightens wood
   • Advantages: Effective on specific stains
   • Disadvantages: Does not remove dirt or kill mold, requires neutralization
4. Sodium Hydroxide (Lye) Cleaners:
   • Active ingredient: Sodium hydroxide (NaOH)
   • pH: Extremely alkaline (13-14)
   • Action: Strips old finishes, cleans deeply, restores gray wood
   • Advantages: Highly effective at removing weathered wood fibers
   • Disadvantages: Can damage wood if left on too long, requires neutralization, corrosive
5. Citric Acid Cleaners:
   • Active ingredient: Citric acid
   • pH: Acidic (3-4)
   • Action: Mild cleaning, brightening
   • Advantages: Environmentally friendly, safe for wood
   • Disadvantages: May not be strong enough for heavy soiling

An overview of a typical cleaning process follows, but this process may vary from deck to deck, particularly depending on the configuration and conditions and materials used in the original construction and level of damage, deterioration, dirt, and debris.:

1. Preparation:
   • Check the deck for structural issues (loose boards, protruding nails)
   • Sweep the deck to remove loose debris
   • Cover nearby plants and any metal fixtures
2. Pre-wetting:
   • Use a hose or pressure washer (low pressure, wide fan tip)
   • Allow for relatively even wetting of all surfaces
   • Allow at least a few minutes for water absorption
3. Cleaner Application:
   • Choose the appropriate cleaner based on the deck’s condition
   • Allow for proper dilution
   • Apply with a pump sprayer, roller, or brush, depending on the circumstances
   • Work in manageable sections (avoid letting cleaner dry out)
4. Scrubbing (if needed):
   • Use a stiff-bristled brush (avoid wire brushes)
   • Scrub with the wood grain
   • Pay extra attention to high-traffic areas and visible stains
5. Dwell Time:
   • Allow the cleaner to work according to manufacturer’s recommendations
   • Do not let the cleaner dry on the surface (mist with water if needed)
6. Rinsing:
   • Use a pressure washer (600-1200 psi, 40-60 degree tip) or garden hose
   • Maintain consistent distance from the deck surface (usually 6-12 inches)
   • Rinse thoroughly, moving with the wood grain
   • Ensure all cleaner residue is removed
7. Neutralization (if required):
   • For acid or strong alkaline cleaners, apply a neutralizing solution
   • Common neutralizers: white vinegar (for alkalis), baking soda solution (for acids)
   • Rinse again after neutralization
8. Drying:
   • Allow the deck to dry completely (usually 48-72 hours, depending on weather)
   • Ensure good ventilation and sunlight exposure if possible
9. Sanding (optional):
   • Once dry, lightly sand the deck with 60-80 grit sandpaper
   • This removes any remaining loose wood fibers and opens the pores for better stain absorption
   • Thoroughly remove all sanding dust

Use a contractor who understands and cares about doing things right.  Always, feel free to reach out to us here at Dupont Decks and Patios.  We are happy to help with almost all steps of the deck building and design process. Let us know about your ideas and talk to us if you have questions about possibilities .  You can call us at (202) 774-9128.  You can find us online at https://dupontdeckspatiosdc.com and you can email us there as well at https://dupontdeckspatiosdc.com/contact-us