Mildew and Mold on Awnings: How to Remove It and Stop It Coming Back

Mildew on an awning is almost always a surface colony living on dirt, pollen and moisture trapped in the fabric, not on the acrylic or polyester fibers themselves. On solution-dyed acrylic you can usually kill and lift it with a diluted bleach and mild soap solution followed by a thorough rinse. This guide covers how to tell mildew from other stains, which mixes are safe on which fabrics, when a stain is permanent, and how to stop it recurring.

Is it mildew, mold, or something else?

Homeowners tend to call any dark speckling "mold." In awning terms, the distinction that matters is not mildew versus mold (both are fungal growth, and they are treated the same way) but fungal growth versus other dark stains that need a different approach.

Location is the strongest clue. Mildew on a retractable awning shows up where moisture lingers: the section of fabric nearest the roller (the last to dry, the first to be rolled up), along the hem pocket at the front bar, along seams, and on the underside where shade keeps it cool.

Why retractable awnings get mildew

Solution-dyed acrylic does not feed mildew. The fibers are synthetic and inert. What mildew eats is the film on top: pollen, bird droppings, tree sap, cooking grease from a grill underneath, spider webs, and plain dust. Add moisture and warmth, and you have a culture medium.

Retractable awnings have a risk that fixed awnings do not: they roll up. A rolled awning is a dark, tightly wrapped cylinder with no airflow. If it goes in damp, every layer stays damp against the next. In summer heat that can mean visible growth within a few days.

• Automatic sensors. Rain sensors and wind sensors retract the awning precisely when it is wet. That protects the frame, but it means you have to remember to extend it again to dry once conditions are safe. More on this in our sun and wind sensor guide.
• Shallow pitch. Water that pools in the middle soaks into fabric and leaves a ring of dirt when it evaporates. If your fabric holds water after rain, see our guide on fixing sag and pitch.
• Trees overhead. Sap and pollen are high-quality mildew food and also hold moisture.
• Closed cassettes in humid climates. A full cassette protects fabric from UV and dirt but traps any moisture inside. It does not cause mildew on its own, but it raises the stakes of retracting wet.
• Seasonal storage. An awning that was retracted slightly damp in October and left closed until April has had six months to develop a colony. This is the classic "it was fine last year" spring discovery.

How to remove mildew, by fabric type

Solution-dyed acrylic (Sunbrella, Recasens, Dickson, Sattler and similar)

Because the pigment is locked into the fiber, solution-dyed acrylic tolerates diluted chlorine bleach without losing color. Sunbrella's published care guidance and the guidance of most other acrylic makers use a bleach and mild soap solution for mildew. If you are unsure whether yours is solution-dyed, see our explainer on solution-dyed acrylic.

1. Extend the awning fully and turn off automation. Work on an overcast, calm day.
2. Brush off loose growth dry. Use a soft brush, outdoors, and avoid breathing the dust.
3. Mix the solution. About 1 cup (240 ml) of regular household bleach and 1/4 cup (60 ml) of mild dish soap per gallon (3.8 L) of clean water. Do not use thickened or "splashless" bleach gels, which are hard to rinse out.
4. Apply and wait. Spray or sponge the solution onto the affected areas and let it soak for up to 15 minutes. Keep it wet; do not let it dry on the fabric.
5. Brush gently. Use a soft brush along the length of the fabric.
6. Rinse thoroughly. Rinse both sides until no trace of bleach smell or suds remains. Residual bleach weakens thread over time and can affect water repellency.
7. Repeat if needed. Heavy colonies can take two rounds. A third round rarely helps; what remains is usually staining, not growth.
8. Dry, then re-treat. Let the fabric dry fully extended, then reapply a fabric water repellent, since bleach strips the factory finish.

Piece-dyed or surface-printed fabric

Do not use chlorine bleach; it will remove color in blotches. Use a cleaner made for outdoor fabric that is labeled safe for colored materials, or an oxygen-based cleaner if the fabric maker permits it, and always test on a hem or the section that stays rolled on the tube first.

Polyester and coated polyester

Many European polyester awning fabrics have a top coating. Mild soap and a soft brush come first. Some makers allow a weak bleach dilution; others do not. Check the care instructions for your specific fabric and test on a hidden area.

Vinyl and vinyl-laminated fabric

Mildew on vinyl usually sits on the surface and wipes off with a vinyl cleaner or soap solution. Heavy staining may respond to a short-contact diluted bleach application, but avoid solvents and abrasive pads, which dull and crack the coating. On laminated fabrics, mildew can grow in the base scrim from the edges and is often impossible to remove.

What not to do

• Do not pressure wash. It drives spores deeper, frays the weave and strips the repellent finish.
• Do not use bleach full strength. Concentrated bleach weakens stitching thread, particularly older polyester-cotton thread, and can yellow some coatings.
• Do not roll it up wet after treating. You will restart the cycle.
• Do not paint on mildew "blockers" meant for walls or decks. They are not formulated for flexible fabric and can stain or stiffen it.

When mildew stains are permanent

After a proper treatment, you may still see faint gray shadows where the colonies were. Usually this means the growth is dead but the pigment it produced has stained the coating, the thread, or the fiber surface. On solution-dyed acrylic, a second bleach round can lighten it further. Beyond that, the remaining marks are cosmetic.

Stains become more likely to be permanent when:

• the growth was left for more than one season
• the fabric is piece-dyed, so bleach is not an option
• the mildew is in stitching thread, which is often more porous than the fabric
• the fabric is laminated and mildew has grown between layers

How to prevent mildew on awnings

• Re-extend the awning after rain once wind has dropped, and leave it out until both sides are dry. In warm weather, aim to dry it within 24-48 hours of a wet retraction.
• Rinse off pollen, sap and droppings during the season. Clean the fabric at least once a year following our cleaning guide.
• Keep water-repellent finish topped up so rain beads and runs off rather than soaking in.
• Maintain enough pitch for runoff. Water that pools feeds mildew.
• Trim branches that overhang the awning where you can.
• Before winter storage, clean and fully dry the fabric. Our winterizing guide covers the end-of-season routine.
• Keep grills away from the underside, both for grease and fire safety.

Health concerns and when to replace the fabric

Outdoor mildew on an awning is generally a cosmetic and fabric-care issue, not the same as indoor mold in a home. Still, people with mold allergies or asthma should avoid brushing dry growth and should let someone else handle the cleaning or wear a suitable mask.

Replace the fabric, rather than keep treating it, when mildew stains coincide with other signs of end of life: seams that tear when pulled gently, fabric that has lost its repellency and no longer responds to treatment, heavy fading, or the fabric has developed permanent sag. Our fabric replacement guide covers measuring and costs.

Frequently asked questions