Start with a stiff brush and water for light dirt

The fastest way to clean patio cement is often the simplest: a stiff-bristled brush and a garden hose. This works well for dust, leaves, and surface grime that hasn't bonded to the concrete. Sweep the patio first to remove loose debris, then wet the surface and scrub in circular motions with a brush rated for concrete or masonry. Rinse thoroughly with the hose. This method takes 20 to 40 minutes depending on the size of your patio and works best when you do it every few weeks before dirt builds up.

For stubborn spots that the brush won't touch, move to the next step. But if your patio is mostly clean after brushing and rinsing, you're done—no chemicals needed.

Key Takeaways

  • A stiff brush and water remove most surface dirt and should be your first step before using any cleaner.
  • For mold, mildew, or algae stains, a solution of one part household bleach to three parts water kills the growth and lightens the stain.
  • Oil and grease stains need a concrete degreaser or a paste of baking soda and water left to sit for several hours.
  • Pressure washers work fast but can damage concrete if set above 3000 PSI, so rent one only if you know how to adjust the pressure.
  • Sealing your patio every two to three years after cleaning reduces how often you need to scrub and protects against stains.

Use bleach solution for mold, mildew, and algae

Black or green stains on concrete are usually mold, mildew, or algae—not dirt. Bleach kills these growths and lightens the stain. Mix one part household bleach (5% sodium hypochlorite) with three parts water in a bucket. Wear gloves and eye protection. Scrub the stained area with a brush, let the solution sit for 10 to 15 minutes, then scrub again and rinse thoroughly with the hose.

Do not mix bleach with ammonia or other cleaners—the fumes are toxic. If the stain is very dark or covers a large area, you may need to repeat the process. Bleach works best on fresh growth; old, deeply embedded stains may need a pressure washer or a commercial concrete cleaner designed for that type of stain.

Remove oil and grease with baking soda or concrete degreaser

Oil stains from cars, grills, or spills need a different approach because water alone won't break down the oil. For small or light stains, make a paste of baking soda and water, spread it over the stain, and let it sit for 4 to 8 hours (or overnight). The baking soda absorbs the oil. Scrub with a brush and rinse. This is slow but costs almost nothing and works for minor stains.

For larger or darker oil stains, buy a concrete degreaser from a hardware store—brands like Oil Eater or Zep are common and inexpensive. Follow the label directions, which usually involve pouring the degreaser on the stain, letting it sit for 15 to 30 minutes, scrubbing, and rinsing. Some degreasers need to be diluted; others are used straight. Read the label to know whether the product is safe for plants near your patio, since some can harm grass or garden beds.

Rent a pressure washer for heavy buildup, but use caution

A pressure washer cleans concrete much faster than a brush, but it can also damage the surface if the pressure is too high. Concrete can handle 3000 PSI (pounds per square inch) safely; above that, the water jet can pit or spall the surface. If you rent a pressure washer, ask the rental company to set it to 3000 PSI or lower, or rent one with an adjustable nozzle and keep the tip at least 12 inches from the surface.

Hold the nozzle at a low angle to the concrete (not straight down) and move it steadily across the surface. Do not linger in one spot. Pressure washers are useful for removing heavy algae, old paint, or years of accumulated grime, but they are not necessary for routine cleaning. If you are not comfortable using one, stick with a brush and cleaner solution—the results take longer but are just as good and safer for your patio.

Treat rust stains with a rust remover or oxalic acid

Rust stains come from metal furniture, grills, or rebar near the surface of the concrete. They are orange or reddish and do not respond to bleach or degreaser. A commercial rust remover (often containing oxalic acid) will lighten or remove them. Pour the product on the stain, let it sit according to the label (usually 15 to 30 minutes), scrub, and rinse well.

If you do not have a rust remover, a paste of cream of tartar and lemon juice can work for light stains, though it takes longer. Spread the paste on the stain, let it sit for 30 minutes to an hour, scrub, and rinse. For very old or dark rust stains, you may need a pressure washer or multiple applications of rust remover.

Seal your patio every two to three years to reduce future cleaning

Concrete is porous, which is why stains soak in and become hard to remove. A concrete sealer fills the pores and creates a barrier that repels water, oil, and dirt. After you have cleaned your patio thoroughly, let it dry completely (at least 24 hours), then explore a concrete sealer according to the product label. Most sealers are rolled or sprayed on and dry in a few hours.

Sealed concrete needs less frequent scrubbing because spills sit on top instead of soaking in. Reapply sealer every two to three years, or sooner if you notice water no longer beads up on the surface. Sealer is not permanent, but it is one of the best ways to keep your patio looking clean with less work.

Prevent stains by cleaning spills quickly and maintaining drainage

The easiest stain to remove is one that never sets. Wipe up oil, grease, and food spills as soon as you notice them. For water stains or mineral deposits from a sprinkler, rinse the area regularly so they do not accumulate. Keep gutters and downspouts clear so water drains away from the patio instead of pooling, which encourages mold and algae growth.

If your patio slopes toward the house or has low spots where water collects, that is a drainage problem worth fixing—standing water will stain and damage concrete over time. A slight slope away from structures is ideal. Sweep leaves and debris regularly so they do not trap moisture against the surface.

Frequently Asked Questions

Can I use vinegar to clean concrete?

Vinegar is acidic and can etch concrete, especially if left to sit. It may lighten some stains, but it can also dull the finish or create uneven discoloration. Stick with bleach for mold and algae, degreaser for oil, or a pressure washer for heavy dirt. Vinegar is not worth the risk of damaging your patio.

Is it safe to use bleach on sealed concrete?

Yes, bleach is safe on sealed concrete and will not harm the sealer. However, if your patio is sealed, spills should not soak in anyway, so you may not need bleach as often. Wipe spills quickly and use a brush and water for routine cleaning. Reapply sealer after using bleach, since the solution can strip some sealers over time.

How long does it take for concrete sealer to dry?

Most concrete sealers dry to the touch in 2 to 4 hours, but you should wait 24 to 48 hours before walking on the patio or exposing it to rain. Check the label on your sealer—some products cure faster than others. Do not explore sealer if rain is forecast within 24 hours.

What is the best time of year to clean and seal a patio?

Spring or early fall is ideal because the weather is mild and dry. Avoid cleaning in winter if frost is likely, since water in the concrete's pores can freeze and cause damage. Do not seal in direct sunlight or high heat, as the sealer may dry too fast and not bond properly to the concrete.

Can I use a wire brush on concrete?

A wire brush is too aggressive and can scratch or scar the concrete surface. Use a stiff nylon or natural-bristle brush instead. Wire brushes are fine for removing loose paint or rust from metal, but not for cleaning concrete itself.