This is right off the Sunbrella website.
Heavy cleaning for
stubborn stains and mildew
Sunbrella fabric does not promote mildew growth,
however, mildew may grow on dirt and other foreign
substances that are not removed from the fabric. To
clean mildew, or other stubborn stains:
• Prepare a solution of 1 cup bleach and 1/4 cup
of mild detergent per gallon of clean water.
• Soak affected area in solution for 15 minutes.
• Remove stain with a sponge or clean towel.
• Rinse thoroughly to remove all detergent residue.
• Air dry.
Remember to protect the area around your
Sunbrella fabric if using a bleach solution. Carpet
or other fabrics that are not Sunbrella may have an
adverse reaction to the bleach. If a boat cover is
suitable in size for a washing machine, these steps
should be followed:
• Use mild detergent.
• For heavier stains add 1 cup of bleach to wash.
• Wash and rinse in cold water.
• Air dry. Never apply heat to Sunbrella.
• Re-treatment for water and stain resistance
will be necessary after machine washing.
Re-treating the fabric
As part of the finishing process, Sunbrella fabrics are
treated with a fluorocarbon finish, which enhances
water repellency. This finish is designed to last
for several years, but must be replenished after a
thorough cleaning. Based on test results,
Glen Raven recommends 303 High Tech Fabric
Guard™ as the preferred re-treatment product for
Sunbrella fabrics. Fabrics should be re-treated after
thorough cleaning or after five years of use.