Prep first
Before you start
- Identify the cause first: location, smell, feel and how it appeared decide the treatment.
- Brush off dry soot and mildew before you wet them.
- Test any cleaner on a hidden spot first.
Black stains on siding can be mildew, soot, manganese from well water or grease, and some marks are damage that won't fully lift. Water is safe on siding, but abrasive scrubbing and pressure equipment both need care, since a deck can be damaged in the wrong hands. Weathered wood and old stain need their own handling, so identify the material before you start.
Black stains on vinyl siding and black stains on exterior walls both start with a gentle wash, so check the material before you add anything stronger. Aluminum and fiber cement each have their own limits, so identify which one you have first. Once you know the surface can take it, a mild detergent wash is the first thing worth trying.
Before you start
What siding, roof & exterior can take
Safe to use2
- Water
- Oxygen bleach
Use with care5
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
4 items
What you'll need
Tap an item to get it on Amazon, or tick what you already have.
- Mild detergentMakes the water wash for vinyl and aluminum siding, and the moistened detergent for stubborn vinyl spots. (opens Amazon)
- Clean water and a garden hoseFor wetting the wall and rinsing; low-pressure hose spray is the recommended rinse.
- SpongeScrubs stubborn vinyl spots after the detergent has sat. (opens Amazon)
- Stiff synthetic-bristle brushScrubs mildewed wood siding along the grain. (opens Amazon)
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6 steps
Step by step
Step 1 of 6
Find the cause and test
Start by working out what's behind the black mark. Location, smell, feel and how it appeared all point to the cause, whether mildew, soot, manganese from well water or damage. Brush or vacuum dry soot and mildew before anything gets wet, and brush mildew off outdoors.
Careful. Don't use chlorine bleach until you know it isn't manganese or iron; bleach can intensify those stains.
Step 2 of 6
Wet the wall and wash bottom-up
Wet the wall surface first. On aluminum or vinyl siding, wash with a solution of water and a mild detergent, working from the bottom up to reduce streaking.
Tip. Cover shrubbery and plantings around the work area with polyethylene plastic.
Careful. Wear rubber gloves and avoid splashing the solution in your eyes.
Step 3 of 6
Rinse vinyl before suds dry
On vinyl siding, rinse the dirty, sudsy area off right away. Work in sections you can rinse before the suds start to dry.
Careful. Don't let cleaners or soap dry on the siding.
Step 4 of 6About 5 minutes
Treat stubborn vinyl spots
Where spots stay after the wash, moisten the detergent and apply it straight onto each stain. Leave it for about 5 minutes, then scrub with a sponge and rinse the spot off.
Step 5 of 6
Scrub mildewed wood along grain
On wood siding, scrub the mildewed boards with a stiff synthetic-bristle brush, working along the grain, using warm water and a mild detergent. Scrub only the mildewed areas and leave clean boards alone.
Step 6 of 6
Rinse well and let dry
Rinse the whole wall with clean water until no suds or cleaner remain. Then let the siding dry completely before you judge the result.
Tip. Use a garden hose on low pressure for the rinse.
If you'd rather buy than mix
Best products for black stains on siding, roof & exterior
For weathered wood, look for a commercial deck cleaner or brightener. For the wash, choose a mild liquid detergent without ammonia.
Dawn Ultra Dish Soap Refill Jug
These are the everyday supplies the steps above use, in the versions most people buy on Amazon.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
Once rinsed and dry, the black should be gone or much lighter, and the siding color should show evenly across the washed area. A dark spot that's still there after drying is likely a set-in mark, and the section below explains what's realistic.
What changes for yours
Adjust for your siding, roof & exterior
Vinyl siding
On vinyl, the wash stays gentle and each sudsy section gets rinsed right away. Stubborn spots get the moistened detergent for about 5 minutes, not stronger chemicals.
Vinyl can't take organic-solvent cleaners, undiluted chlorine bleach, liquid grease remover, nail polish remover or furniture polish, so keep those out of the bucket. If a spot survives the detergent, stop there rather than escalating.
Aluminum siding
Aluminum gets the same water and mild detergent wash as vinyl, working from the bottom up so streaks don't set. Keep baking soda off it, because it's unsafe on aluminum even as a gentle scrub.
Work one panel at a time and rinse each one before moving on. If the stain still shows after that, don't reach for stronger cleaners; the set-in section explains what's realistic.
Fiber cement siding
Fiber cement needs the gentlest approach of the three. Wet the wall first, then wash gently from the bottom up and rinse before anything dries. Skip the high-pressure power washer, bleach, acid, hard metal brush and abrasive sponge, since they can damage the surface and finish.
If a mark survives a gentle wash, stop there rather than moving to stronger tools. The professional section below covers when to call for help.
Heavy or long-standing buildup
Old black marks that have set into wood may not come out completely. Some black is damage rather than dirt, and old moisture or burns in wood finishes can stay after cleaning. Weathered, grayed wood can often be brightened, though, once the mildew and dirt are gone.
For an old dark moisture ring on wood, chlorine bleach is the option, but only after the wood has been rinsed. Sponge the bleach around the stain and then onto it, rinse, and repeat if needed. It lightens the wood, so the spot may end up paler than the boards around it.
Some marks stay no matter what you try. If the wood has lost all its natural color, it stays silver when dry, and those fibers should be left in place. A clean, even surface is the realistic goal, not a perfect return to the original color.
Vinegar, baking soda, peroxide and more
Do home remedies work on black stains on siding, roof & exterior?
Most home remedies you'll find online were written for fabric, countertops or other surfaces. Here's how each one fits siding, and the steps above are the only ones you need.
Skip5Avoid1
What makes it worse
Mistakes to avoid
Don't paint over mildew
Mildew keeps growing under paint, so the black will come back through the new coat. Clean the area, rinse it, and let it dry completely before any paint goes on.
Don't aim a pressure washer upward
Vinyl siding shouldn't be hit with a pressure washer aimed upward, so keep any spray angled down. Stubborn spots are better handled by the detergent step than by more pressure.
Don't use steel wool or wire brushes
Leftover iron from steel wool or wire brushes reacts with the wood's natural extractives and leaves stains. Stick with a stiff synthetic-bristle brush along the grain on wood siding.
Don't power wash soft wood or scrub caustic
Western redcedar and other soft woods can lose their surface to a power washer, and caustic cleaners scrubbed hard do the same. Keep wood siding to the gentle wash and brush in the steps.
Don't mix bleach with ammonia or acids
Bleach mixed with ammonia, or with a detergent that contains it, forms a toxic gas, so keep ammonia out of the bucket. Bleach also shouldn't meet acids such as vinegar, and you should rinse thoroughly between products.
When to call a professional
If the black is still there after the steps and the wood looks damaged, a professional can judge whether anything more can be done. Pressure washing is the part to leave to someone experienced, since siding can be damaged in the wrong hands.
Questions
Can I use bleach on black stains on vinyl siding?
Not undiluted, because vinyl can't take it. Start with the water and mild detergent wash, and check the cause before any bleach goes near the siding.
Why does the black come back after I clean it?
Mildew keeps growing, so it can return if the first wash didn't remove all of it. Rinse fully, let the wall dry, and look again before deciding it's set in.
Can I pressure wash aluminum siding?
Don't assume a pressure washer is safe on aluminum, so start with a hand wash. If you do use one, keep the spray low and angled down.
What if I can't tell what's causing the black?
Look at the location, smell, feel and how it appeared, since those clues decide the treatment. If you're still unsure, test the detergent wash on a hidden spot before using anything stronger.
Can weathered gray wood siding be restored?
Often yes, with a commercial cleaner or brightener that removes mildew and dirt so the wood's color shows. If the natural color has leached out, the wood stays silver when dry, and those fibers are best left in place.
Is fiber cement siding treated the same way?
Yes, but go gentler. Start with the gentlest wash and skip the tools and sprays that can damage it, which are listed in the fiber cement section below.
Black Stains on other materials
Other stains on siding, roof & exterior
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.