Aluminum siding collects oxidation, mildew, chalky white residue, and general grime that makes a house look older than it is. You can clean it effectively with a solution of dish soap, oxygen bleach, and water — applied with a soft brush or a pressure washer on a low setting. Plan for a half-day project on an average-sized home. Here’s the right approach that cleans without scratching or denting the aluminum panels.
What You’ll Need
- Garden hose with spray nozzle (or pressure washer at 1,200–1,500 PSI)
- Oxygen bleach cleaner (Oxiclean, Jomax, or similar) or dish soap
- Household bleach (for mildew — diluted)
- Large bucket
- Soft-bristle long-handled scrub brush
- Pump garden sprayer
- Safety goggles and rubber gloves
- Drop cloths for plants
- Car wash mitt or sponge (for hand cleaning small sections)
- Aluminum oxidation remover or automotive polish (for heavy oxidation)
Safety and Precautions
Work from a ladder safely — have a helper hold the base when working above the first story. Wear goggles and rubber gloves when handling bleach or oxygen bleach solutions. Wet down nearby plants and grass before applying any cleaning solution to reduce chemical uptake. Never use steel wool, abrasive scrubbers, or high-grit sanding on aluminum siding — these permanently scratch the surface and remove the protective coating. Do not use 0 or 15-degree pressure washer nozzles on aluminum siding — the concentrated stream dents and deforms the panels.
Step 1: Inspect the Siding
Before cleaning, walk around the house and identify the specific problems: heavy white oxidation chalking, green or black mildew stains, rust streaks from iron fasteners, oil stains, or general grime. This assessment determines which cleaning solutions and methods you’ll need for each area. Sections with active mildew need a bleach treatment; sections with oxidation may need a separate oxidation-removal product after the main cleaning.
Step 2: Pre-Rinse the Siding
Wet the entire exterior with the garden hose or pressure washer before applying any cleaning solution. This pre-rinse removes loose dirt and surface debris, and prevents cleaning solution from absorbing too quickly into dusty or dry siding. Work from top to bottom so you’re not spraying dirty water onto already-rinsed areas.
Step 3: Mix and Apply the Cleaning Solution
For general cleaning: mix 1/4 cup of dish soap or oxygen bleach cleaner per gallon of warm water in a bucket or pump sprayer. For mildew: add one cup of household bleach per gallon of water to the oxygen bleach solution, or treat mildew areas separately. Apply the solution to the siding using a pump sprayer or brush, working top to bottom in sections of 10–15 linear feet. Let the solution dwell on the surface for five to ten minutes — don’t let it dry.
Step 4: Scrub with a Soft Brush
Use a soft-bristle long-handled scrub brush to work the cleaning solution into the siding surface. Scrub horizontally, following the direction of the siding panels. Apply consistent, moderate pressure — aggressive scrubbing isn’t needed and can scratch the aluminum coating. Pay extra attention to horizontal ledges, seams, and the areas around windows and trim where grime accumulates thickest.
Step 5: Rinse from Top to Bottom
Rinse the cleaned sections thoroughly from the top down using the garden hose or pressure washer at a downward angle. Water directed upward under the siding panels can penetrate behind the siding and cause moisture problems. Work in smooth horizontal passes, overlapping each pass. Rinse until the water running off is completely clear and no soap residue remains.
Step 6: Treat Remaining Mildew or Stains
Inspect the siding after it has dried slightly. Persistent black or green mildew spots that remain after the main wash can be spot-treated with a cloth or brush dampened with a solution of one cup bleach per gallon of water. Apply to the stain, let sit for five minutes, then rinse. For rust streaks from screws or nails, apply a rust remover formulated for exterior surfaces, let dwell per product directions, and rinse.
Step 7: Address Oxidation (If Present)
Aluminum oxidation appears as a chalky, dull white haze that doesn’t wash off with normal cleaning. After the siding is clean and dry, apply an aluminum oxidation remover or automotive paste polish to oxidized areas using a soft cloth. Work in small sections using circular motions, then wipe clean. This restores some of the surface coating luster. For entire-house oxidation, this is a significant additional project — a professional siding restoration service may be more practical.
Pressure Washing Aluminum Siding
Pressure washing is the fastest method for large homes. Use 1,200–1,500 PSI maximum with a 25-degree (green) or 40-degree (white) nozzle. Keep the wand 18–24 inches from the siding surface. Direct water at a downward angle — spraying upward under panel edges forces water behind the siding. Apply cleaning solution first, let it dwell, then pressure wash off for best results. Never use high-pressure settings (above 1,500 PSI) on aluminum siding — it dents the panels and can buckle them permanently.
How Often to Clean Aluminum Siding
Clean aluminum siding every one to two years in most climates. In humid, shaded areas where mildew develops aggressively, annual cleaning is worth doing. In dry climates with full sun, two-year intervals are typically sufficient. An annual inspection each spring helps you identify developing mildew or oxidation before it becomes a significant cleaning project.
Pro Tips
- Clean on a cloudy day: Full sun causes cleaning solution to dry before it can work. Overcast conditions give the solution time to penetrate and do its job.
- Start from the top: Always start at the top and work down. Cleaning solution dripping onto uncleaned sections pre-treats those areas naturally. Running dirty water across already-cleaned siding re-soils it.
- Check caulking and trim: While cleaning, inspect all caulk joints around windows, doors, and trim. Deteriorated caulk allows moisture intrusion — cleaning season is a good time to identify caulk that needs replacement.
- Don’t clean in freezing temperatures: Water trapped behind siding panels can freeze and expand, causing damage. Clean when temperatures are above 40°F and will stay above freezing for 24 hours.
Frequently Asked Questions
What is the white chalky residue on my aluminum siding?
That chalky white film is aluminum oxidation — the result of the aluminum reacting with oxygen and UV light over time. Regular cleaning removes dirt and mildew but doesn’t eliminate oxidation, which requires a dedicated aluminum oxidation remover or polish applied after the siding is clean and dry.
Can I use a pressure washer on aluminum siding?
Yes, with the right settings. Use 1,200–1,500 PSI maximum, a 25 or 40-degree nozzle, and keep the wand 18–24 inches from the surface. Direct water downward, not upward. These limitations prevent denting and water intrusion behind the panels.
How do I remove black streaks from aluminum siding?
Black streaks are typically mildew or algae. Treat with a diluted bleach solution (one cup bleach per gallon of water) using a scrub brush, let sit five minutes, then rinse thoroughly. For streaks that originate near roof lines, they may be caused by roof algae runoff — cleaning the roof algae eliminates the source.
Will bleach damage aluminum siding?
Diluted household bleach (one cup per gallon) used as directed is safe for aluminum siding. Extended contact time (more than 10–15 minutes) or undiluted bleach can potentially etch the surface coating. Always dilute properly and rinse promptly.
Should I repaint or coat aluminum siding after cleaning?
Not necessarily after every cleaning, but if the existing paint is chalking heavily, peeling, or the oxidation is extensive, repainting after a thorough cleaning significantly restores the appearance. A 100% acrylic latex exterior paint bonds well to cleaned aluminum and provides years of protection.
Conclusion
Cleaning aluminum siding is an annual or biannual maintenance task that extends the life of your home’s exterior and dramatically improves curb appeal. The combination of an oxygen bleach solution, a soft scrub brush, and a thorough top-to-bottom rinse handles most conditions. For oxidation, a separate treatment step after cleaning restores the surface luster. For other exterior home maintenance projects, check out our guide on how to clean a metal roof — the same algae and oxidation challenges apply to metal roofing with specific solutions for each.
