How to Clean Pavers: Moss, Algae and Stains

Why pavers get dirty and turn green

Concrete pavers are porous, so they absorb water, and with it dirt and algae spores. In shaded and damp spots, at ground level, on the north side or under trees, the surface stays wet longer. That is exactly where green deposits appear first and moss grows in the joints.

On top of that come everyday stains. On the driveway these are oil and grease, on the terrace leftovers of food and drink, and everywhere dust, sand and decaying leaves. The longer they sit, the deeper they penetrate and the harder they are to remove later.

Regular cleaning solves two things at once. It restores the look and removes the damp layer of dirt in which microorganisms develop. As a result the stone ages more slowly and new green growth returns later.

Types of dirt and how to recognise them

Choosing the method starts with recognising the problem, because different types of dirt need different products.

• Green and black deposits are algae and moss. They appear on damp, shaded spots and return as long as moisture remains.
• General dirt, dust and deposits from rainfall. These come off with cleaning using a product and water.
• Oil and grease stains, typical on driveways. They need a grease dissolving product.
• Rust, for example from metal furniture, tools or fence parts. A separate type of stain and a separate product.
• Efflorescence, a whitish deposit on concrete. A natural process removed with dedicated products.

What to clean pavers with

For everyday dirt and green growth there are paver cleaners. They act on the layer of dirt and on microorganisms, so the deposit comes off more easily than by scrubbing alone. For special stains, that is oil, rust and efflorescence, you use products intended for the given purpose.

Whatever the product, read the label. It states the use, the dwell time, the recommended dilution and the safety precautions. Different products have different requirements, and the product data sheet is decisive here.

When to clean

It is most convenient to clean pavers in dry, rain free weather and above freezing, when the product can work and the surface can dry afterwards. Full heat is not ideal, because the product dries too quickly. Mild, warm days work better.

If you plan to seal the pavers after cleaning, schedule both tasks with time to spare. The pavers must dry thoroughly first before you apply the protective product.

What to prepare before cleaning

• A brush with stiff bristles and a broom for moss and loose dirt.
• A paver cleaner, and if needed a product for specific stains.
• Water, a garden hose or a pressure washer on a moderate setting.
• Gloves, goggles and other protective equipment stated on the product data sheet.
• Joint sand, because after thorough cleaning some is usually missing.

Cleaning pavers step by step

1. 1
   Remove moss and loose dirt. Clear moss and weeds from the joints and sweep away sand and leaves. A brush with stiff bristles handles most loose dirt.
2. 2
   Dampen the surface if the product requires it. Some products work better on slightly dampened pavers. Check this on the label before you start.
3. 3
   Apply the cleaner. Spread the product evenly and let it dwell for the time stated on the pack. Do not let it dry out completely unless the instructions allow it.
4. 4
   Scrub the harder spots. Brush over joints, corners and heavily overgrown areas. That is where dirt holds on most strongly.
5. 5
   Rinse thoroughly with water. Rinse off the dissolved dirt and product residue. Work so that no streaks remain, ideally rinsing evenly in one direction.
6. 6
   Top up the joint sand. After cleaning and drying, add sand where it is missing. The joints keep the pavers in one plane.

Difficult stains, that is oil, rust and efflorescence

We treat these three problems separately, because they do not come off with ordinary cleaning.

• Oil and grease. The faster you react, the better. Blot a fresh stain first, cover it with an absorbent material and then use a grease dissolving product according to the instructions.
• Rust. Ordinary cleaners usually do not remove it. You need a product for rust, and the stain often has to be treated several times.
• Efflorescence. The whitish deposit on new stone is a natural process. Part of it goes away over time, the rest you remove with a product for efflorescence.

What to do after cleaning the pavers

Freshly cleaned and dried pavers are the best moment for protection. A protective product limits water absorption, so dirt and water get in more slowly and new green growth returns later. In other words, cleaning removes the problem and protection slows its return.

How to choose and apply the protective product we describe in the guide on sealing pavers.

How to keep pavers clean for longer

• Sweep away sand and leaves, because lying dirt holds moisture and encourages moss.
• Remove stains immediately, before they penetrate the structure.
• Watch the water drainage, because standing water is the shortest path to green growth.
• Consider protecting the surface, which noticeably shortens later cleaning.

The most common mistakes when cleaning

• Too high pressure from the washer, which rinses out the joints and damages the surface.
• Letting the product dwell too long or too short, against the instructions.
• Insufficient rinsing, which leaves streaks and residue.
• Mixing different chemicals on your own.
• Sealing the pavers before they have dried thoroughly after washing.