How we test outdoor cleaners
Our testers applied each cleaner to either dirty wooden decking or patio squares heavily covered in algae growth and dirt, as appropriate. We left non-treated areas around the test sections for comparison.
The product was left on for as long as recommended and, after cleaning off as relevant, we assessed the results. We looked at cleaning power and how hassle-free (or otherwise) the products are to apply.
We noted if any smelt particularly unpleasant and found most weren't too bad, especially after dilution.
You don't want new stains or marks appearing to replace the ones you've just cleaned off the patio. Most of the ones we tested didn't, but some left noticeable white marks.