I get asked this a lot, especially after a wet spring. The short answer? Use a mix of white vinegar and water, plus some elbow grease, and always protect yourself. But let me break it down properly because the material matters.
First, identify what your bench is made of. Most urban benches are either wood (often teak or pine), powder-coated metal, recycled plastic, or a combination. Each needs slightly different care.
Safety first: mold spores aren't something you want to breathe in. Grab an N95 mask, rubber gloves, and safety glasses. Also, if the bench is in a busy public area, try to clean it early in the morning when fewer people are around, and maybe put up a small “wet bench” sign if you can.
For wood benches (which seem to hold mold the worst), start by dry-brushing off any loose surface mold with a stiff nylon brush. Do this away from your face, and ideally on a dry day. Then mix one part white vinegar with one part water in a spray bottle. Vinegar kills about 82% of mold species and won't damage the wood like bleach can. Spray the entire affected area generously, let it sit for 15-20 minutes, then scrub with a stiff brush. Rinse with clean water, and let it dry completely in the sun if possible. For stubborn dark stains, you can add a tablespoon of baking soda to the vinegar mix to make a paste.
If you're dealing with powder-coated metal or plastic benches, you have an easier job. Mix a few drops of mild dish soap with warm water and scrub the mold off with a sponge or soft brush. For persistent mold, use a solution of 1 part bleach to 10 parts water (never use bleach on wood—it can break down the fibers). Apply with a spray bottle, wait 10 minutes, scrub, and rinse thoroughly. Bleach is harsher, so test it on a small hidden spot first to make sure it doesn't discolor the finish.
Now, the prevention part is key. Mold loves shade and moisture, so if the bench sits under a tree or in a damp corner, consider trimming back branches to let in more sunlight, or suggest to your local council that they apply a waterproof sealant to wooden benches each year. A quick wipe-down after heavy rain also goes a long way.
One last tip: don't use a pressure washer. It might seem faster, but it can force water deep into wood or damage paint, creating even better conditions for mold to grow back.
So, to summarize: identify the material, protect yourself, use vinegar for wood or mild bleach for metal/plastic, scrub, rinse, dry, and prevent future growth. It's not glamorous, but it works.