Maybe you don't own a pressure washer. Maybe you do, but your patio is older than you are, already flaking at the edges, and you've got a feeling it won't survive the experience.
Either way, you're not stuck. A pressure washer mostly buys you speed. Brushes, the right chemistry, and a little patience do most of the actual cleaning.
Here's what works, what doesn't, and how to tell which category your concrete falls into.
Should Your Concrete Skip the Pressure Washer Anyway?
Run through this list before anyone rents a machine. If any of these describe your slab, clean it by hand.
- The surface is flaking, pitted, or sandy. A pressure washer peels off more of the weakened layer. Here's why concrete flakes.
- It's old and soft on top. Drag a key or screwdriver across an out-of-the-way spot. If it scratches easily or sheds grit, the surface is weak.
- It's stamped, colored, or exposed aggregate. High pressure can scour color and dislodge stones. See types of concrete finishes.
- It has a glossy sealer on it. Film-forming sealers, common on decorative concrete, can be scuffed or stripped by a strong jet.
- It's less than about a month old. New concrete is still curing.
- The joints are open along the house. Spraying into joints and the foundation gap pushes water, and soil with it, under the slab. That's how voids start.
- It was just caulked or patched. Fresh sealant can tear.
Hand-Cleaning Methods at a Glance
| Method | Good for | Avoid when |
|---|---|---|
| Stiff nylon brush + detergent | General dirt, traffic lanes, pollen, light grime on any concrete | Rarely a bad idea; it's just slow on a big driveway |
| Garden hose with a jet nozzle | Rinsing, flushing grit, salt residue | Aimed into joints along the house |
| Oxygen bleach | Mildew, algae, leaf and berry stains, brightening dull concrete | The stain is rust or oil; it's the wrong chemistry |
| Diluted chlorine bleach | Stubborn black mildew in deep shade | Near ammonia or acid products, or near plants you haven't wetted down |
| Dish soap or degreaser + scrubbing | Fresh grease, food spills, light oil | The oil has soaked in for months |
| Absorbent (kitty litter, sawdust) | Fresh oil and fluid spills | The spill has already dried into the surface |
| Poultice | Old oil, deep stains, stains that reappear after washing | Large areas; it's a spot treatment |
| Rust remover made for concrete | Rust rings, fertilizer speckles | Bleach was used nearby and not rinsed off |
| White vinegar | Very little on concrete | Repeated use, sealed or decorative concrete, anywhere near bleach |
Spot-test anything new on a hidden corner first, especially on colored or stamped concrete.
The Basic Scrub, Done Right
Nothing fancy here, but the details are where hand cleaning succeeds or fails.
- Timing beats elbow grease. Cleaner that dries on hot concrete leaves a film and stops working. A cool, cloudy morning beats a sunny July afternoon, and a patch you can finish and rinse before it dries beats one big push.
- Nylon, not wire. Wire brushes scratch the surface, and broken steel bristles can leave rust specks behind.
- Get the grit off. Sand left over from winter turns your cleaning solution into mud.
- Wet the slab before the cleaner goes on. A pre-soaked surface keeps the solution up top where the dirt is, instead of letting it wick into dry pores.
- Let the chemistry work. Give it the dwell time on the label, and mist it if it starts drying out.
- Scrub across the grain, then with it. Broom-finished concrete has tiny ridges, and one direction only cleans one side of them.
Oxygen Bleach: The Workhorse for Green and Black Growth
That green or black film on the walk along the north side of your house is usually mildew, mold, or algae. It thrives where concrete stays damp and shady, and it's slippery when wet.
Oxygen bleach is the powdered kind, made from sodium percarbonate. It dissolves into hydrogen peroxide and washing soda, and the peroxide breaks down into water and oxygen. There's no chlorine in it, which makes it easier to live with near lawns and gardens.
Mix it fresh, following the package (warm water helps it dissolve), and use it soon after. Pour or brush it on the wet slab, keep it wet while it works, then scrub and rinse. Leaf stains and berry spots usually respond to the same treatment.
If the growth keeps coming back, look up. A downspout emptying onto the walk keeps that spot wet all season. Extending the downspout does more than any cleaner. For heavy growth, see our mold and mildew guide.
About chlorine bleach: diluted per the label, it works on stubborn mildew. Wet nearby plants first, rinse everything well, and never let it meet ammonia or acids. That combination releases toxic gas.
Poultices for Stains That Soaked In
Concrete is porous. An oil stain that's been there since last summer isn't on the surface anymore; it's in the concrete. Scrubbing only reaches the top.
A poultice works the other way: it pulls the stain out. You mix a fine absorbent powder (whiting, talc, or fuller's earth) with a liquid that dissolves the stain, into a paste about as thick as oatmeal. For oil, that liquid is typically a solvent such as mineral spirits.
- Spread a thick layer that runs well past the edges of the stain.
- Let it dry completely, usually about a day. As the liquid evaporates, it draws the stain up into the powder.
- Brush it off and look. Old stains often take two or three rounds.
- Ventilate and skip open flames when working with solvents, and keep the paste off nearby plants.
Our oil stain guide and general stain guide cover which liquid goes with which stain.
The Vinegar and Baking Soda Question
Every cleaning shortcut list mentions these two. Here's the reality on concrete.
Vinegar is an acid. Acids react with the cement paste that holds concrete together. One rinsed-off application won't ruin a driveway, but using it as your regular cleaner slowly roughens the surface, makes it more absorbent, and can break down sealer. And because it's an acid, it must never meet chlorine bleach.
Baking soda and vinegar cancel each other out. The fizz is carbon dioxide. Once it stops, what's left is mostly salty water with very little cleaning power. The bubbles look busy, but that's about it.
Baking soda on its own is a mild abrasive and can soak up a little of a fresh spill. For oil, plain clay kitty litter is the usual go-to.
Getting More Out of a Garden Hose
A hose won't blast anything off, but used well it does more than people expect.
- Use the jet setting, not "shower" or "flood." A tight stream flushes loose dirt out of textured concrete.
- Rinse high to low and away from the house. Dirty water should run off toward the yard, not back across clean concrete or toward your foundation.
- Keep sections wet until you've rinsed them, so loosened dirt doesn't dry back in place.
- Push puddles with a squeegee or broom onto grass or gravel. Storm drains empty into local waterways without treatment, so soapy water shouldn't go down them.
- Watch the thermometer in spring. In March and early April, wait for a stretch above freezing so rinse water doesn't turn into ice on the walk.
What to Leave on the Shelf
- Muriatic acid. It's a strong acid that etches concrete and gives off harsh fumes. It has specialized uses, but routine cleaning isn't one of them.
- Mixing products. Bleach plus ammonia, or bleach plus any acid (vinegar and many rust removers included), produces toxic gas. One product at a time, rinsed between.
- Hard scrubbing on flaking concrete. Use a softer brush and a light touch, or you'll scrub off more of what's left.
- Sealing right after cleaning. Sealer needs dry concrete. Wait for the slab to dry out completely first.
When It's More Than a Weekend Job
Everything above is DIY, and on a patio, a front walk, or a set of steps, it's a good use of a Saturday. You don't need us for that.
Hand-scrubbing a whole driveway is a different story. Call us when:
- You want it sealed afterward. We clean and seal plain outdoor concrete with a penetrating sealer, in that order, with the drying time in between. (For a glossy reseal on stamped or decorative concrete, we'll refer you to a specialist.) Here's how our sealing works.
- It's a big area and your back has opinions about it.
- The stains haven't budged after a couple of honest tries.
And if your concrete is too fragile for pressure washing, we'll tell you that from your photos instead of blasting it anyway.