Nothing ruins your outdoor enjoyment faster than spotting fuzzy black mold or slimy green algae on your deck boards. Not only is it unsightly, but mold can also weaken wood fibers, create slippery surfaces, and trigger allergies. The right deck mold removal approach can restore your outdoor space safely and effectively.
In this guide, we’ll cover proven methods to eliminate mold from both treated and untreated wood, plus prevention tips. For stubborn cases, consider using a specialized mold-killing solution before scrubbing.
Key Takeaways
- Bleach solutions work best for untreated wood; vinegar or detergent for painted/stained decks
- Always scrub with the grain to avoid damaging wood fibers
- Prevent regrowth with proper drainage and sunlight exposure
- Wear gloves and goggles when handling mold or chemicals
1. Identify the Type of Growth
Before treating your deck, determine whether you’re dealing with:
- Mold – Fuzzy black, green, or white patches that penetrate wood
- Mildew – Flat gray or white surface growth
- Algae – Slimy green film common in shaded areas
Mold requires the most aggressive treatment, as it can cause structural damage over time. Test a small area first when using bleach or other strong cleaners.
2. Gather Your Supplies
You’ll need:
- Stiff-bristle brush (nylon for composite, natural bristle for wood)
- Cleaning solution (see table below for options)
- Garden sprayer or bucket
- Protective gear (gloves, goggles, mask)
| Deck Type | Best Cleaning Solution |
|---|---|
| Untreated wood | 1 part bleach + 4 parts water |
| Painted/stained wood | 1 cup vinegar + 1 gallon water |
| Composite decking | Oxygen bleach + water |
3. Apply the Cleaning Solution
Scrub with bleach solution, rinse thoroughly, let dry completely. For best results:
- Wet the deck first to prevent chemical absorption
- Apply solution and let sit 10-15 minutes (don’t let it dry)
- Scrub along the grain to avoid splintering
For composite decks, use a gentler outdoor cleaner to avoid discoloration.
4. Rinse and Dry
Use a garden hose or pressure washer (<500 PSI) to remove all cleaner residue. Ensure proper drying:
- Wait 24-48 hours before sealing or staining
- Improve airflow by trimming nearby vegetation
- Use a leaf blower to remove standing water
5. Prevent Future Growth
Stop mold from returning with these proactive measures:
- Apply water-repellent sealant annually
- Keep deck clear of leaves and debris
- Ensure proper slope and drainage (1/4″ per foot)
- Use mildew-resistant cleaners monthly
When to Call a Professional
Seek expert help if:
- Mold covers more than 10 sq. ft.
- Deck shows structural softening
- You suspect toxic black mold (Stachybotrys)
With these steps, your deck will stay mold-free and ready for outdoor enjoyment. For more outdoor cleaning tips, check out EPA’s mold guidelines or our guide on wood deck maintenance.