The first warm Saturday in May, you pull the cover off the grill and see the patio for what it is. A dark shadow where the grill sat. Orange rings where the planters spent last summer. Brown leaf prints from October. A green corner by the downspout.
Patios get dirty differently than driveways: cooking grease, potting soil, furniture, shade, and birds instead of salt and tire marks. And many patios are stamped or colored, which changes what's safe to use.
Here's how to get it clean without leaving stripes or faded color behind.
Two Things to Check Before You Start
What finish is it? Plain broom finish (fine ridges, gray), stamped or colored (patterned like stone or brick, often with a sheen), or exposed aggregate (pebbles showing on top). Not sure? See our guide to concrete finishes.
Is it sealed? Sprinkle some water on a clean spot. If it beads or sits on top, there's a working sealer, and a glossy one is likely a film-forming acrylic. If the concrete darkens and soaks it up within a minute or so, it's bare or the sealer has worn off. That tells you how gentle to be and which sealer can go back on later. (Some penetrating sealers don't bead much, but they still slow the darkening.)
Patio Type: What's Safe and What to Avoid
| Patio type | Safe methods | Avoid |
|---|---|---|
| Plain broom finish | Pressure washer with a wide fan tip at a steady distance, or a rotary surface cleaner; stiff nylon brush; oxygen bleach; degreaser | Narrow or zero-degree tips, holding the nozzle close (etches the surface, leaves stripes), wire brushes |
| Stamped or colored | Garden hose, mild dish soap, and a push broom; low pressure only for stubborn spots; cleaners labeled safe for sealed or decorative concrete; test spots first | High pressure (damages the sealer and texture), acids, harsh solvents or degreasers not labeled sealer-safe, chlorine bleach without a test |
| Exposed aggregate | Medium-bristle brush; moderate pressure with a fan tip kept moving; surface cleaner; oxygen bleach | A tight, close jet that cuts into the cement paste between the stones and loosens them; strong acids that eat that paste |
On any finish, a cleaner that's new to you gets tested on a hidden spot first.
Keep Spray and Chemicals Where They Belong
- Plants and lawn. Soak the beds with plain water before using any cleaner, loosely cover delicate plants, and rinse everything afterward. Chlorine bleach whitens and kills the leaves it lands on.
- Siding. Keep the spray level or pointed down. Spraying upward can force water behind vinyl siding.
- Doors, windows, and vents. Don't blast thresholds, weatherstripping, window seals, outlets, or dryer vents.
- Your AC unit. Keep spray off the condenser fins. They bend easily.
- Runoff. Green Bay's storm drains carry water to local waterways and the bay without treatment. Keep cleaning chemicals on your property and out of the street.
Patio Stains, One at a Time
Treat stains before the overall wash. A general wash brightens the concrete around a stain and leaves the stain looking worse by contrast.
Planter and furniture rings
White, crusty rings are minerals left by water draining through the pot. A stiff brush and water handle most; heavy buildup may need a masonry cleaner made for mineral deposits, which is usually acidic, so test it on colored concrete and rinse well. Orange or brown rings are rust, from metal pots or chair feet, fertilizer that contains iron, or iron-rich water. Use a rust remover labeled for concrete, test it first, and see removing rust from concrete. Next year, set pots on feet so the slab can dry.
Leaf and tannin prints
Brown or orange leaf shapes come from tannins in leaves that sat wet on the slab. Sun and rain fade many of them over time. To speed it up, apply an oxygen bleach solution, keep it wet for the dwell time, scrub, and rinse.
Grill grease
Fresh drips: cover them with an absorbent like clay cat litter, grind it in with your shoe, and sweep it up after a few hours. Then scrub with dish soap or a concrete degreaser and hot water. Old, dark shadows: expect several rounds of degreaser, or a poultice that pulls oil out of the pores as it dries. On stamped concrete, make sure the degreaser is sealer-safe. More in how to clean oil off concrete.
Green or black film in the shade
That's algae or mildew, usually on the shady side, under a tree, or where a downspout drains. Oxygen bleach or a cleaner labeled for algae and mildew handles most of it. If it returns every summer, see cleaning mold off concrete for the drainage side of the problem.
Bird droppings
Let them dry, scrape them off with a plastic putty knife, then wash with dish soap and water. For a heavy buildup under a perch, wet it down before scraping instead of dry-sweeping, so you're not kicking up dust.
One rule for all of it: rinse thoroughly between products and never mix them on the slab. Chlorine bleach plus ammonia or any acid, including vinegar and many rust and mineral removers, releases toxic gas.
A Patio Cleaning Day That Works
Here's how we'd lay out the day on our own patio: one dry day to clean, at least one more to dry.
The night before
Check the forecast for two dry days in a row. Move furniture, the grill (cooled), and planters onto the lawn, and take a quick photo of what was under each one. Those spots will need their own treatment.
Morning: dry work first
Blow or sweep off everything loose. Scrape moss and weeds out of the joints, and knock off grease crust and droppings. Doing this dry keeps debris from turning into mud and washing into the joints.
Late morning: plants, then stains
Soak the beds. Put absorbent on fresh grease. Treat rust and mineral rings and rinse them completely. Then apply oxygen bleach or your algae cleaner over the organic stains. Work in shade or on an overcast day so nothing dries on the surface.
Midday: the overall wash
Let the slope pick your starting point: begin at the uphill end so runoff keeps moving onto concrete that's still dirty. On stamped or colored concrete, use the hose, mild soap, and a push broom. On a broom finish or exposed aggregate, keep the surface cleaner or wand moving at an even pace. Flush the joints and look at the caulk while you're down there.
Afternoon: rinse and look
Rinse the plants again. Watch where the rinse water goes. If it runs toward the house or puddles by the door, make a note (more on that below).
The next day: check it dry
Stains look different on dry concrete. Walk it in the sun, spot-treat any ghosts, and decide whether you're sealing.
Spring or Fall?
Spring cleaning makes sense once the trees finish dropping pollen and seeds, so you're not doing it twice. Fall works well for sealing, since the slab goes into winter protected, as long as you beat the cold: sealers list a temperature range on the label (one silane product we checked calls for 50–90°F air and surface temperature), and in a Green Bay October that window closes fast. Clearing leaves before the first snow also prevents next spring's tannin prints.
Sealing After the Wash
A clean, dry patio is the only kind worth sealing.
- Broom finish and exposed aggregate: A penetrating silane or siloxane sealer soaks in instead of forming a film. It doesn't change the look or the traction, it lets the concrete breathe, and it resists water and salt.
- Stamped and colored: These are usually sealed with a film-forming acrylic that brings out the color and sheen. It wears faster, so plan on resealing every 2–3 years, and ask for an anti-skid additive because a fresh film can be slippery when wet. A penetrating sealer can't soak through an existing film, so don't mix types without stripping first. We don't do glossy acrylic reseals on stamped or decorative concrete; we'll clean it and point you to a decorative concrete specialist for the sealer. Our sealing work is penetrating sealers on plain outdoor concrete.
- Dry means dry. Give it at least a day after washing, longer in shade or cool weather.
- New patio? Let it cure first. The wait is on the sealer's label; one product we checked calls for at least 7 days, and some want longer.
Doing more than cleaning? On a combined job, the order is: clean, let it dry, lift any sunken slabs, patch the holes, caulk the joints, then seal once the caulk has cured. Joint sealants need bare, clean concrete to grip, so sealing first can keep the caulk from bonding.
If Your Patio Has Sunk or Tips Toward the House
Cleaning day is when a lot of people notice it. The rinse water runs to the back door. A puddle sits against the foundation. There's a gap between the slab and the house that wasn't there before.
A patio should pitch away from the house. If yours has settled the wrong way, foam lifting can raise it back to the right slope through a few dime-sized holes, and you can walk on it right away. Then seal the gap at the house so water stays out. See caulking where concrete meets the house.
If one slab was pushed up by a tree root instead, that's a different problem. Foam only raises concrete, so read tree roots lifting concrete before you call anyone.