How to Wash a Deck

Using a combination of chemical restoration and medium pressure cleaning is one of the fastest ways to restore a deck’s appearance and remove slippery buildup. Done correctly, it can lift years of dirt, algae, and weather stains in a single afternoon. Done incorrectly, it can scar the wood, cause splintering, and lead to costly repairs. Here’s a practical, step-by-step guide to pressure washing your deck safely and effectively.

Step 1: Clear and Prepare the Area

Remove all furniture, planters, and decorations from the deck. Sweep away debris like leaves, dirt, and twigs.

Close nearby windows and doors to prevent water from entering your home.

Step 2: Apply a Cleaner and Scrub

Before pressure washing, it’s important to break down embedded dirt, old stains, and organic buildup. Either sodium metasilicate or sodium percarbonate are good cleaners for this purpose, either by themselves, or as an ingredient in a commercially available wood cleaner. They can loosen grime and prepare the surface for rinsing.

How to apply:

1. Dilute your cleaner as appropriate.
   
   

2. Apply evenly using a pump sprayer or watering can.
   
   

3. Let it dwell for 10–15 minutes without drying.
   
   

4. Scrub the surface using a stiff-bristle deck brush, working with the wood grain.
   
   

This step lifts deep contaminants and reduces the amount of pressure needed later, helping prevent wood damage.

Step 3: Choose the Right Settings

Using too much pressure, too narrow of a nozzle, or spraying too close to the wood are the most common mistakes homeowners make.

For wood decks:

• Use a low to medium pressure setting
  
  

• Choose a 40-degree spray nozzle for gentle, even cleaning
  
  

• Test the pressure on an inconspicuous area first
  
  

Softwoods like cedar and pine require lower pressure than hardwoods. If you notice fuzzing or splintering, reduce the pressure immediately.

Step 4: Pressure Wash with Proper Technique

Hold the spray wand about 6–12 inches from the surface. Always spray in the direction of the wood grain to avoid visible marks.

Best practices:

• Use long, even strokes,  following the entire length of each board without stopping
  
  

• Keep the nozzle moving continuously
  
  

Start at one end of the deck and move methodically toward the other. Overlapping each pass slightly ensures uniform cleaning. The goal is to rinse away loosened dirt — not strip the wood.

Step 5: Rinse Thoroughly

After washing, give the entire deck a final rinse with clean water. This removes leftover cleaner and loosened debris. Proper rinsing prevents residue from drying onto the wood and affecting future staining or sealing.

Step 6: Apply Oxalic Acid to Brighten the Wood

After pressure washing, many decks still show greying or dark tannin stains. Oxalic acid is a wood brightener that restores a more natural appearance.

How to apply:

1. Mix oxalic acid according to product instructions. In the case of a pure powder, mix 1 cup into 1 gallon of warm water.
   
   

2. Apply evenly across the damp deck using a pump sprayer.
   
   

3. Let it sit for 15–10 minutes or until effects are visible.
   
   

4. Rinse thoroughly with clean water.
   
   

This step significantly improves the final appearance

Common Mistakes to Avoid:

• Using too much pressure, too narrow of a nozzle, or spraying too close

• Skipping the cleaning agents

• Stopping halfway along a board

• Going against the grain

• Ignoring safety precautions
   

If you’re unsure about tackling the job yourself, professional deck cleaning can save time, reduce risk, and deliver longer-lasting results, so Call Blue Wave today at (647) 212-6460 for a free estimate on deck cleaning in the Niagara region.