This whole process, on my inflatable, takes less than 10 minutes and requires absolutely no rubbing. Simply apply with the chip brush and watch it eat away the stains. Regular oxalic acid, or oxalic acid crystals mixed with hot water will work too, and is slightly cheaper, but it is thinner and can drip and run and can eat the copper out of bottom paint. The gel stays put for the most part with considerably less dripping.