By April, the concrete around most Green Bay homes looks tired. There's a white crust on the apron where the salt sat all winter, a dark lane where the cars park, a green film on the walk along the north side of the house, and a few orange dots nobody can explain.
Most of that comes off. Some won't, and some of the ways people attack it do more harm than the stain ever did. This is the big-picture guide; where a stain deserves its own playbook, we link to it.
Start by Naming the Stain
A degreaser does nothing for rust, and bleach does nothing for oil. Spend two minutes identifying what you're looking at.
| Stain | How to recognize it | What usually removes it | Full guide |
|---|---|---|---|
| Winter salt residue | White, crusty film or wavy "tide lines," worst on the apron and where cars drip | Plain water and a stiff brush, repeated. It dissolves. | Spring concrete maintenance |
| Efflorescence | White powder that crumbles when rubbed, dissolves in water, and comes back after wet weather; often near cracks, edges, and steps | Dry brushing first, then a rinse. It means water is moving through the concrete. | Removing stains from concrete |
| Rust | Orange-brown rings under furniture and planters, speckles where fertilizer landed, streaks under railings | A rust remover made for concrete. Many are acidic, so rinse well and keep bleach away. | Removing rust from concrete |
| Leaves, berries, droppings | Brown leaf silhouettes, purple or red spots under trees | Oxygen bleach and a scrub brush. Sunlight fades a lot of it over time. | Removing stains from concrete |
| Oil and grease | Dark blotches that look wet even on a dry day, usually where vehicles or the snowblower sit | Absorbent on fresh spills, degreaser and scrubbing, a poultice for old stains | Cleaning oil off concrete |
| Mold, mildew, algae | Green, black, or gray film in shady, damp spots; slick underfoot when wet | Oxygen bleach, or chlorine bleach diluted per the label, then scrub and rinse | Cleaning mold off concrete |
| General grime | Overall gray dullness, darker lanes where you walk and drive | Detergent and scrubbing, or a pressure washer with a surface cleaner | Keep reading |
Salt residue and efflorescence both show up white. The difference: salt residue appears where deicer was used and rinses away for good. Efflorescence can show up anywhere moisture moves through the slab, and it keeps coming back until the water source is dealt with.
Garage stains, like hot tire marks, are their own topic. See cleaning concrete floors. For surface-specific advice, we have guides for driveways and patios.
Choosing a Method
| Method | Best for | Risk to the concrete | Effort |
|---|---|---|---|
| Stiff brush, detergent, garden hose | Patios, steps, small walks, older or flaking concrete, stamped or sealed surfaces | Very low | High on big areas |
| Pressure washer with a rotary surface cleaner | Driveways, long walks, and big patios in sound condition | Low when set up right | Low to moderate |
| Pressure washer, wand only | Edges, steps, corners, rinsing | Moderate to high. Most stripes and etching come from this. | Moderate |
| Chemical treatments (oxygen bleach, degreasers, rust removers, poultices) | Specific stains a wash won't touch | Varies. Acids can etch, chlorine bleach can burn plants. | Low effort, but needs dwell time |
The brush-and-bucket route
A concrete cleaner or mild detergent, a stiff nylon push broom, and a hose clean more than people expect. Wet the slab first, work in sections small enough that the solution doesn't dry on the surface, and rinse each section before moving on. Skip wire brushes on most concrete; they scratch, and broken steel bristles can leave rust specks behind. Our full hand-cleaning guide is here.
Pressure washer plus a surface cleaner
A rotary surface cleaner is a round hood with spinning nozzles underneath. It holds the spray at a fixed height and keeps it moving, so every square foot gets the same treatment. That's what gives flatwork an even, stripe-free finish. Use the wand only for edges and tight spots, and work from the high side of the slab to the low side so dirty water runs off concrete you haven't cleaned yet.
Chemical treatments
Treat stains before the general wash, not after. Follow the label on dwell time, keep the product wet while it works, and rinse it completely. Matching the chemistry to the stain matters far more than buying the strongest jug on the shelf.
Pressure Washer Mistakes That Leave Permanent Marks
Concrete looks indestructible, but its top layer is cement paste, and a concentrated jet cuts it. Once it's etched, it stays etched: rough, sandy, and quicker to hold dirt than before.
- Using the red tip. On most machines, quick-connect tips are color coded: red 0°, yellow 15°, green 25°, white 40°, and black for soap. The red tip is a pencil-thin jet that carves lines in concrete. Leave it in the box.
- Going too narrow or too close. Common homeowner guidance is a green 25° tip for flatwork, or white 40° for rinsing, held a foot or more off the surface.
- Parking the spray. Holding the jet on one spot to "really get it" is exactly how you dig a groove. Keep it moving.
- Wand-washing a whole driveway. Each pass cleans at a slightly different distance and speed, and you end up with stripes. That's the surface cleaner's job.
- Chasing more pressure. Common homeowner guidance for driveways is roughly 2,000 to 3,000 PSI. More than the job needs just makes etching easier.
- Blasting joints and the house gap. Aiming the jet into control joints, cracks, or the gap along the foundation drives water (and the soil it carries) under the slab. That's how voids under concrete get started.
- Washing concrete that's already flaking. Pressure peels off more of the weakened surface. Scrub it by hand instead. Here's what causes the flaking.
Before you commit, test your setup on a corner nobody looks at.
When to Clean in Northeast Wisconsin
| When | Why | What to do |
|---|---|---|
| After the thaw | Salt residue and brine keep working on concrete until they're gone | Rinse and scrub the apron, garage approach, walks, and joints |
| Summer | Warm, dry days; algae and organic stains peak | Deep clean and treat stains |
| Late summer to early fall | Good window to clean, let it dry, and seal before winter | Clean, wait for a dry slab, seal |
| After the leaves drop | Wet leaves left on concrete leave tannin stains | Clear leaves before they sit, treat what's left |
| Winter | Rinse water freezes on the slab | Skip it, other than a salt rinse on an above-freezing day |
Clean before you seal, every time. Sealer can't soak through dirt or oil, and it locks in whatever stain it goes over. It also needs dry concrete; one data sheet we checked called for at least 24 hours of drying after rain. More in why seal concrete and choosing a concrete sealer.
Where the Wash Water Goes
Storm drains generally don't go to a treatment plant. They carry water to the nearest creek, river, or the bay, untreated. Anything you wash into the street gutter goes along for the ride.
- Route it to grass or gravel. Plan your rinse direction so water soaks into the yard instead of running down the driveway into the street.
- Start with water and scrubbing. Use the least chemical that works.
- Pick up absorbents. Oil-soaked kitty litter goes in the trash (or wherever your municipality directs), not swept into the gutter.
- Protect plants. Wet down nearby plants before using bleach, and rinse them again as you work.
- Ask locally if you're unsure. Rules on wash water vary by municipality.
Safety: The Rule You Can't Break
Never mix chlorine bleach with ammonia or with acids. Bleach plus ammonia makes chloramine gas. Bleach plus an acid releases chlorine gas. Both can seriously damage your lungs.
On concrete, the acid part catches people off guard. Vinegar is an acid. So are many rust removers and masonry cleaners. If you hit the mildew with bleach, rinse the area thoroughly before you treat rust nearby, and never combine two products in one bucket or sprayer.
A few more:
- Eye protection, gloves, closed-toe shoes. Cleaners splash, and pressure washers kick up grit.
- Respect the jet. A pressure washer stream can cut skin and push water and dirt into the tissue underneath. That's an ER trip even if the wound looks small.
- Ventilate. Solvents and degreasers in a closed garage add up fast.
- Keep kids and pets off until it's rinsed.
When to Call Us
Cleaning a patio, a front walk, or one stain is a good DIY project, and you don't need us for it. Call us when:
- It's the whole driveway and you'd rather not spend a weekend behind a pressure washer.
- The staining is heavy, or you've already tried the usual fixes.
- You want it sealed afterward. We offer cleaning and sealing together, so the slab gets cleaned, dried, and sealed in the right order.
- Something else needs work too. On a combined job, the order matters: clean, let it dry, lift any sunken slabs, patch the drill holes, caulk the joints, then seal once the caulk has cured. See our concrete cleaning process and our sealing process.
One honest note: some stains don't come out completely. Oil that soaked in years ago, long-standing rust, and leaf shadows on porous concrete may lighten a lot without disappearing. We'll tell you from your photos what's realistic before you spend anything.