Mold on a patio has a way of creeping in quietly, then suddenly your outdoor space looks dirty, smells musty, and feels slick underfoot. It’s not just an eyesore. Mold and mildew can make concrete dangerously slippery, and if you ignore it long enough, it can stain the surface and keep coming back even after you rinse.
The good news is that mold on concrete is usually very fixable with the right process. The bad news is that many DIY cleanups fail because people skip prep, use the wrong chemical, or blast the surface with pressure and spread the spores around.
This guide walks you through a safe, repeatable way to remove mold from a Concrete Patio, plus how to prevent it from returning. You’ll learn what causes mold on concrete, how to choose the right cleaning method, the best cleaners for different levels of growth, and what to do when mold keeps coming back in the same spots.
Before You Start: Mold vs Mildew vs Algae
People use “mold” as a catch-all term, but patios often have a mix of organic growth. It helps to know what you’re looking at, because the cleaning approach is similar, but prevention can differ.
- Mold: Often looks dark (black, brown, green) and can feel fuzzy or patchy. It thrives in damp, shaded areas.
- Mildew: Usually a lighter film or powdery layer, sometimes gray or off-white, often with a musty smell.
- Algae: Typically green, slimy, and most common where sprinklers or runoff keep the concrete wet.
On concrete, the biggest issue is moisture. Mold grows when water lingers, shade reduces drying, and organic debris (leaves, dirt, pollen) feeds the growth. If you clean the surface but keep the moisture conditions the same, the patio may look better for a few weeks, then slowly turn green and black all over again.
Safety First (And Don’t Forget Your Landscaping)
Mold cleanup is mostly about chemical control and thorough rinsing. That means you’ll be working with cleaning solutions that can irritate skin, eyes, and lungs. It also means runoff can affect nearby plants if you aren’t careful.
- Wear gloves and eye protection. If you’re spraying a cleaner, use a basic mask too.
- Keep kids and pets away until the patio is fully rinsed and dry.
- Pre-wet plants and soil with clean water before applying any cleaner.
- Cover delicate plants if you’re using stronger solutions, but don’t trap heat for long.
- Work on a calm day so overspray doesn’t drift into landscaping or walls.
If your patio drains toward a gutter or storm drain, use minimal product and rinse thoroughly. Avoid letting concentrated cleaner run off into waterways. The goal is effective cleaning with controlled application, not flooding the area with chemicals.
What You’ll Need
You can remove mold without fancy equipment. The essentials are: remove loose debris, apply the right cleaner evenly, give it time to work, scrub where needed, then rinse until the runoff is clear.
Basic tools
- Broom or leaf blower
- Stiff nylon brush (avoid wire on stamped or colored concrete)
- Garden hose with spray nozzle
- Bucket for mixing solutions
- Pump sprayer or watering can for even application
Optional but helpful
- Wet/dry vacuum for low spots and puddles
- Pressure washer (used carefully) or surface cleaner attachment
- Soft washing setup (low pressure sprayer) for solution-driven cleaning
Cleaning solutions (choose based on severity)
- Light growth: mild patio cleaner or diluted vinegar solution
- Moderate growth: oxygen bleach (sodium percarbonate) solution
- Heavy growth: commercial concrete-safe mold/mildew remover
If your patio is stamped, colored, coated, or previously sealed, avoid harsh acids and test any cleaner in a small hidden spot first. Even a “safe” cleaner can react differently depending on the concrete finish.
Step-by-Step: How to Remove Mold from a Concrete Patio
This process works for most patios and can be adjusted based on how stubborn the mold is. The biggest mistakes people make are: applying cleaner to a dirty surface, letting it dry during dwell time, and rinsing too quickly.
Step 1: Clear the patio and sweep thoroughly
Remove furniture, planters, mats, and anything that traps moisture. Then sweep the entire surface, including edges and corners. Leaves and dirt are not harmless. They break down, feed mold, and stain concrete over time.
If you have thick, stuck-on debris, use a hose to loosen it and sweep again. You want the surface exposed so your cleaner can reach the growth.
Step 2: Pre-wet the concrete
Lightly wet the patio with clean water. Pre-wetting helps the cleaning solution spread evenly and reduces the chance of the concrete absorbing cleaner too quickly. It also helps prevent streaks.
Don’t flood the surface. You want damp concrete, not a patio covered in standing water.
Step 3: Apply your chosen mold-killing solution
Apply the solution evenly using a pump sprayer or watering can. Work in manageable sections so you can keep the cleaner wet during dwell time. Dwell time matters because the solution needs time to kill spores and loosen the biofilm.
Step 4: Let it dwell (but don’t let it dry)
Most cleaners need about 5 to 15 minutes to work, depending on the product and how heavy the growth is. If the surface starts drying, lightly mist it with water to keep it active. Letting it dry early is one of the easiest ways to get uneven results.
Step 5: Scrub the problem areas
On many patios, mold will loosen and rinse away with minimal scrubbing. But shaded corners, grout-like expansion joints, and textured finishes may need agitation. Use a stiff nylon brush and scrub in overlapping passes.
Focus on:
- Edges near landscaping
- Areas near sprinklers or downspouts
- Shaded sections that stay damp
- Traffic lanes where dirt mixes with growth
Step 6: Rinse thoroughly until the runoff is clear
Rinse from the high side of the patio toward the low side so dirty water moves away from cleaned areas. Keep the water moving. If you leave residue behind, it can dry into streaks and attract dirt faster later.
If you see patches still clinging after rinsing, reapply cleaner to those spots, scrub lightly, and rinse again. Two controlled passes beat one aggressive pass every time.
Step 7: Let it dry completely and inspect
Concrete can look “clean” when wet, then show staining again as it dries. Give the patio time, then inspect. If dark stains remain but the slimy or fuzzy growth is gone, you may be dealing with deep staining rather than active mold. That calls for a stain-focused approach, not just a stronger mold killer.
Best Cleaning Solutions for Mold on Concrete
The “best” cleaner depends on how heavy the growth is and how sensitive your patio surface is. Below are reliable options and when they make sense.
Option 1: Oxygen bleach (great all-around choice)
Oxygen bleach (often sold as sodium percarbonate) is a popular option because it’s effective on organic growth and generally safer for landscaping than harsh alternatives when used properly. It also helps lift staining and brightens the concrete.
Mix according to the product instructions, apply evenly, allow dwell time, scrub where needed, and rinse thoroughly. If you have heavy mold in shaded spots, you may need a second pass.
Option 2: White vinegar solution (best for light growth)
Vinegar can help with mild mildew film, especially if you’re doing routine maintenance. It’s not always strong enough for heavy mold and may not fully kill deep spores in porous concrete. If you try it and growth returns quickly, upgrade to oxygen bleach or a dedicated concrete-safe mold remover.
Option 3: Commercial concrete-safe mold/mildew remover (best for heavy growth)
For patios with thick black staining, slick algae-like buildup, or recurring growth that returns quickly, a commercial cleaner designed for concrete can be the most predictable option. Follow label directions carefully, control overspray, and don’t let the product dry on the surface.
Always test first if the patio is stamped, colored, coated, or sealed. Some strong cleaners can alter the appearance of decorative finishes.
Pressure Washing vs Soft Washing for Mold Removal
Pressure washing can remove visible growth fast, but it can also cause problems when used incorrectly. It may etch the surface, leave zebra-striping, or push water and spores deeper into cracks and pores. Soft washing relies on the cleaning solution to do most of the work, with low pressure rinsing to finish.
When pressure washing makes sense
- The patio is in good condition with no fragile or crumbling areas
- You’re using a wide fan tip and controlled technique
- You’ve already applied a cleaner to kill and loosen growth
How to pressure wash without damaging concrete
- Use a wide fan tip (25° or 40°), not a zero-degree tip.
- Keep the nozzle moving. Never linger in one spot.
- Start farther away and only move closer if needed.
- Consider a surface cleaner attachment to reduce streaks.
- Test a small, hidden section first.
When soft washing is the better choice
- The patio is older, worn, or has decorative finishes
- Mold is widespread and tied to shade and moisture
- You want longer-lasting results by killing spores first
If you only blast growth off the surface without killing it first, you can get a short-term improvement that fades quickly. Solution-first cleaning usually lasts longer.
What If Mold Keeps Coming Back?
If mold returns within weeks, it’s usually because the conditions never changed. Cleaning is only half the battle. You also need to make the patio a less friendly place for growth.
- Fix sprinkler overspray: If sprinklers hit the patio daily, mold will keep winning.
- Improve drainage: Standing water invites algae and mildew.
- Trim plants: Dense landscaping traps shade and humidity near the slab.
- Move moisture traps: Rugs, planters, and stacked items can hold water against concrete.
- Clean organic debris sooner: Wet leaves and pollen feed growth.
In some cases, a sealer can help by reducing absorption and making future cleaning easier. But sealing over moisture problems can cause hazing or peeling. Make sure the concrete is fully dry and the drainage is reasonable before sealing.
Dealing With Stains After Mold Is Gone
Sometimes the mold is dead and removed, but a shadow remains. That’s staining, not active growth. The fix depends on the cause. Oxygen bleach often helps lighten organic stains with a second treatment and gentle scrubbing.
If staining is very dark and persistent, you may have years of buildup embedded in the surface, especially on older porous slabs. In that case, consistent maintenance cleaning and addressing moisture are the real long-term answers. Trying to “force” perfect uniform color can lead people into overly aggressive methods that damage the concrete.
Quick FAQ
Is mold on concrete dangerous?
Mold on a patio is often more of a slip hazard than a health hazard outdoors, but it can still irritate allergies and it can track indoors. The slick surface is a real risk, especially after rain or early morning dew.
Can I use bleach to remove mold from a patio?
Some people use diluted bleach, and it can work, but it’s rough on landscaping and can discolor nearby materials. It also doesn’t always clean as evenly as people expect on porous surfaces. If you use it, protect plants, dilute properly, and rinse thoroughly. Many homeowners prefer oxygen bleach or a concrete-safe mold remover for more controlled results.
How often should I clean mold off my patio?
If your patio is shaded or stays damp, a light maintenance cleaning every few months can prevent heavy growth. Many patios do well with a deeper clean once or twice a year, plus occasional spot treatments in problem corners.
Why does mold grow faster in certain areas?
Mold concentrates where water lingers: shaded edges, low spots, areas hit by sprinklers, and places blocked from airflow. Those areas need both cleaning and a moisture reduction plan.
When should I call a professional?
If the patio is heavily stained, very large, has delicate decorative finishes, or you’re dealing with recurring growth that comes back quickly despite cleaning, a professional service may save time and reduce the risk of surface damage.