How to Clean Exterior Grout
Wet the surface with a garden hose, spray grout cleaner onto the joints, let it sit for 5 minutes, scrub with a stiff brush, and rinse thoroughly. While cleaning, inspect for cracked or missing grout and note areas that need repair.
- Time
- 45 min
- Frequency
- once a year (spring)
- Difficulty
- easy
- Cost
- $8
What you'll need
- Stiff-bristle brush
- Garden hose with spray nozzle
- Grout cleaner
- Safety glasses
The steps
- 1
Wet the surface with a garden hose
Pre-wet the entire area with a garden hose. This prevents the grout cleaner from being absorbed too quickly into dry grout and porous stone or concrete. It also loosens surface dirt and debris so the cleaner can work on the deeper stains.
- 2
Spray grout cleaner on the joints
Apply Zep Grout Cleaner & Brightener or a similar product directly onto the grout lines. Work in sections of about 20 to 30 square feet so the cleaner does not dry before you scrub. Wear safety glasses. Grout cleaners contain mild acids that can irritate eyes on splashback.
- 3
Let it sit for 5 minutes
Give the cleaner time to break down mold, algae, and ground-in dirt. Do not let it dry on the surface. If the area is in direct sun, work in smaller sections or spray the surface lightly with water to keep it damp. Five minutes is enough for most stains.
- 4
Scrub with a stiff brush
Use a stiff-bristle brush and scrub along the grout lines. A deck brush on a long handle works well for large areas like patios so you do not have to work on your knees. For stubborn mold or algae, apply more cleaner and scrub a second time. Use a smaller hand brush for edges and corners.
- 5
Rinse thoroughly
Rinse the entire area with a strong stream from the garden hose. Start at the high end and work downhill so dirty water flows away from cleaned areas. Make sure all cleaner residue is removed. Leftover cleaner can discolor grout or damage surrounding plants.
- 6
Inspect for cracked or missing grout
While the grout is still damp from cleaning, examine every joint for cracks, crumbling, and missing sections. Damp grout shows damage more clearly than dry grout. Poke suspect areas with a screwdriver. If grout crumbles out, it needs repair.
- 7
Note areas needing repair
Use your phone to photograph any joints with cracked, crumbling, or missing grout. Note the locations so you can plan a regrouting session. Small patches can be filled with premixed grout. Large areas of failure may indicate a drainage or substrate problem that needs professional evaluation.
Where exterior grout lives
Exterior grout shows up in more places than most homeowners realize. Patios with stone or tile have grout between every joint. Walkways, front stoops, and steps often have grouted stone or brick. Retaining walls with stone veneer, outdoor fireplaces, and stone facade accents on the house all use grout.
Each of these locations is exposed to rain, snow, UV, and biological growth year-round. Unlike interior grout that mostly deals with shower water, exterior grout faces freeze-thaw cycles that crack weakened joints, constant moisture that feeds mold and algae, and dirt that grinds into the porous surface with every footstep.
Annual cleaning is the minimum. It removes the biological growth and staining before they cause permanent discoloration, and it gives you a chance to inspect the structural condition of every joint while you are already down there working.
Why cleaning and inspection go together
Combining cleaning and inspection in one session is deliberate. Dirty grout hides damage. A grout line covered in mold or algae may look intact from a distance, but once you scrub it clean you find cracks, crumbling, or voids underneath.
Damp grout also reveals damage better than dry grout. Cracks that are invisible when dry become obvious when wet because the water wicks into the crack and darkens it. This is why the inspection step comes after cleaning and rinsing, while everything is still wet.
Catching damaged grout early matters because the damage accelerates. A hairline crack lets water in. In winter, that water freezes, expands, and widens the crack. The next thaw lets more water in. Within one or two freeze-thaw seasons, a hairline crack becomes a crumbling void. Cleaning once a year catches cracks while they are still cheap and easy to patch.
When to regrout vs just clean
If the grout is stained, green with algae, or darkened with mold but structurally sound, cleaning is all you need. Scrub it, rinse it, and consider sealing it afterward to slow future staining.
If the grout is cracked, crumbling at the edges, or missing in spots, cleaning alone will not fix it. You need to remove the damaged grout with a grout saw or oscillating tool, then pack fresh grout into the joint. Small patches of damage are a straightforward DIY repair. Widespread crumbling across a large area suggests a substrate or drainage problem. Water may be pooling under the surface and eroding the grout from below. Get a professional opinion before regrouting the whole area only to have it fail again.
Preventing mold and algae
Mold and algae grow where moisture lingers and sunlight is limited. On exterior grout, this usually means north-facing surfaces, shaded patios under tree canopy, and any area where water pools instead of draining.
Fix drainage first. If water pools on your patio, no amount of cleaning prevents regrowth. Adjust the grade so water flows away from the surface, or add drainage channels.
Trim overhanging branches and shrubs to increase sun exposure and air circulation. Mold and algae cannot compete with direct sunlight and moving air.
After cleaning, apply a penetrating grout sealer. Sealed grout absorbs less moisture, which gives mold and algae less to feed on. Reapply the sealer every one to two years for outdoor surfaces that get constant water exposure.
Frequently asked questions
- What is the best time of year to clean exterior grout?
- Spring is ideal. You are cleaning off winter dirt, mold, and algae before summer use. The moderate temperatures are good for working outdoors, and if you find damaged grout, you have the full season to schedule repairs before winter freeze-thaw cycles make the damage worse.
- Can I pressure wash exterior grout instead of scrubbing?
- You can, but use caution. High-pressure water can blast grout out of joints, especially if the grout is already weakened. Keep the nozzle at least 12 inches from the surface and use a fan tip, not a pinpoint. For sanded grout between pavers, hand scrubbing with cleaner is safer and more effective.
- When should I regrout instead of just cleaning?
- Regrout when the grout is cracked, crumbling, or missing in sections. If you can poke a screwdriver into the grout and it crumbles, cleaning will not fix it. Cleaning addresses surface stains and biological growth. Structural failure of the grout requires removal of the damaged material and fresh application.
- How do I prevent mold and algae from growing on exterior grout?
- Improve drainage so water does not pool on the surface. Trim back plants that shade the area, since mold and algae thrive in damp shade. After cleaning, apply a penetrating grout sealer to reduce moisture absorption. Sealed grout resists biological growth much better than unsealed grout.
Products you'll need
This section contains affiliate links. We may earn a commission at no cost to you.
Zep Grout Cleaner & Brightener
Spray-on grout cleaner for tile and stone
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