Honestly, the best way to remove moss from a concrete street bench is a combination of dry scraping, a simple cleaning solution, and a stiff brush. You usually don’t need a pressure washer, and you don’t want to reach straight for chlorine bleach.
Start by clearing loose debris. Use a plastic putty knife or an old plastic scraper to lift off the thickest moss. Work carefully so you don’t scratch or gouge the concrete surface. This dry pass makes the wet cleaning much easier and reduces the amount of moss you’ll wash into the surrounding soil.
Next, choose your cleaner. For most moss on concrete benches, I’d mix one part distilled white vinegar with one part warm water and add a small squirt of dish soap. The vinegar kills the moss, while the soap helps the solution cling to the surface. Spray or brush the mixture liberally over the mossy areas and let it sit for 20 to 30 minutes. Don’t let it dry completely. If it starts drying, give it a light mist with water.
If the moss is thick, black-stained, or very stubborn, use oxygen bleach instead. Mix about one cup of sodium percarbonate or oxygen bleach powder into one gallon of warm water. Apply it to the bench, let it work for 15 to 20 minutes, then scrub. This is safer than chlorine bleach for nearby plants and concrete color.
After the soak, scrub the concrete bench with a stiff nylon brush or a deck brush. Work in circles and get into the rough texture of the concrete. Rinse thoroughly with a garden hose or buckets of clean water. If any green film remains, repeat the spray-and-scrub process before moving on.
For heavy buildup, a pressure washer can speed things up, but keep the pressure low and use a fan tip. A narrow high-pressure stream can etch concrete and leave it more porous, which actually invites moss to return.
Once the bench is clean and dry, consider applying a penetrating concrete sealer. It won’t make the concrete slippery like a film-forming coating, but it will help reduce moisture absorption and slow moss regrowth. Also trim back overhanging branches, sweep the bench regularly, and improve drainage around the base if water pools there.
Avoid using rock salt or harsh acid-based cleaners on concrete street furniture. They can damage the surface and harm nearby landscaping. If you want a commercial moss killer, look for one labeled safe for concrete and follow the label exactly.
That routine—scrape, soak with vinegar or oxygen bleach, scrub, rinse, and seal—is the best balance of safe, cheap, and effective for most concrete street benches.