Constantly exposed to rain and other wet natural elements, canvas awnings are particularly susceptible to the invasion of water-loving moss. Routine cleanings will help prevent this problem, but if you have neglected your awnings and moss has accrued, it's not too late. A little hard work and some careful planning can make your awnings look like new again.
Sweep the outside of the awning clean of all dust, twigs and other debris. Use a ladder to access hard-to-reach spots.
Apply oxygen bleach (such as OxyClean) to the awning's surface, placing special emphasis on mossy spots. Depending on the size of the awning, spread the bleach using either a chemical sprayer or a simple spray bottle.
Scrub the awning gently with a brush until all moss has been uplifted.
Rinse the awning completely clean using the spray gun on the water hose. Begin spraying at the top and work down to avoid streaks.
Spread fabric sealant (such as ReggTopp) on the newly clean awning to help prevent future water and moss damage.
Repeat Steps 1 through 5 on the underside of the awning.
There are many chemical cleaners available for awnings, as well as various chlorine bleach solutions. However, an oxygen bleach-based cleaning solution is recommended to protect nearby plants and avoid toxic runoff. If you are cleaning a large awning, you might try applying the cleaner and scrubbing it in stages. Letting the cleaning solution sit for too long can have an unpleasant drying effect, resulting in streaks.