How to Remove Mold and Mildew From an Awning (and Keep It Away)
Quick answer
Mildew grows on the dirt, pollen and moisture sitting on awning fabric, not usually on the fibers themselves. On solution-dyed acrylic, treat it with 1 cup of bleach and 1/4 cup of mild soap per gallon of water, let it soak 15 minutes, scrub gently and rinse thoroughly; on polyester and vinyl, use a cleaner the fabric maker approves instead of bleach. Prevent it by never leaving fabric rolled up wet.
To remove mildew from an awning, first identify the fabric. On solution-dyed acrylic (Sunbrella and similar), apply a mix of 1 cup household bleach and 1/4 cup mild soap per gallon of water, let it sit about 15 minutes, scrub with a soft brush, rinse until the water runs clear, and air dry fully. On coated polyester and vinyl, skip bleach and use a mildew cleaner labeled safe for that material. Then fix the cause: almost every mildew problem on a retractable awning traces back to fabric that was rolled up damp or rarely cleaned.
This guide focuses on mold and mildew. For routine washing, soap ratios and frame care, see the full guide on how to clean an awning.
Why awnings get mildew
Mildew is a surface mold. It needs three things: moisture, mild temperatures and something to eat. Synthetic awning fabrics such as acrylic, polyester and vinyl are not good food for mold, but the film of pollen, dust, bird droppings, sap and soap residue on them is. That is why a clean awning rarely mildews and a dirty one does even in dry climates.
Conditions that drive growth:
- Retracting while wet. A rolled canopy holds moisture between layers for days or weeks. Mildew often appears as regular stripes matching the roll's wraps.
- Shade and poor airflow. North-facing walls, awnings under trees, and units tucked into corners dry slowly.
- Ponding. Low pitch lets water sit in a belly in the fabric. Retractable awnings should run at least about 14 degrees (about 3 inches of drop per foot of projection) to drain; see awning projection and pitch.
- Humidity. The EPA notes that keeping indoor relative humidity below about 60 percent limits mold growth. Outdoors you cannot control humidity, so drying time and cleanliness become the levers.
- Soap residue. Incomplete rinsing after cleaning leaves an easy food source.
Is it mildew, dirt or something else?
Before treating, confirm what you are looking at. Mildew typically shows as clusters of small black, gray or green dots, often with a musty smell, and it spreads over weeks. Dirt streaks follow the drainage path and wash off with plain soap. Rust stains (orange-brown) come from fasteners or the frame and need a different approach. Tree sap feels sticky. Spot test with the routine soap mix first; if the dots do not budge, treat it as mildew.
Treatment by fabric type
| Fabric | Bleach OK? | Recommended treatment | Main risk |
|---|---|---|---|
| Solution-dyed acrylic | Yes, diluted | 1 cup bleach + 1/4 cup mild soap per gallon of water, 15 minute dwell | Strips water repellent; weakens thread if not rinsed |
| Coated or laminated polyester | Usually no | Mild soap, then a mildew cleaner labeled safe for coated fabrics | Bleach can fade dyes and degrade the coating |
| Vinyl and vinyl-coated polyester | Check maker | Vinyl awning or RV awning cleaner; soft brush | Solvents and abrasives damage the surface |
| PVC-coated mesh | Check maker | Mild soap, back-rinse, cleaner approved by maker | Weave distortion from scrubbing |
| Cotton or cotton blend canvas (older awnings) | No | Mild soap; persistent mold usually means replacement | Mold digests cotton fibers and weakens them |
Note: Mildew on synthetic fabric usually lives on the surface. On cotton canvas it feeds on the fibers themselves, so stains are often permanent and the fabric loses strength. Cotton is rare on modern awnings for this reason.
Step-by-step mildew removal (acrylic)
- Protect yourself and surroundings. Wear gloves and eye protection. Wet down plants, decking and siding below, and cover anything sensitive. Never mix bleach with ammonia or acidic cleaners.
- Extend and dry brush. Open the awning fully and brush off loose spores and debris with a soft brush, working away from you and downwind.
- Pre-clean with soap. Wash the affected area with the routine mix (1/4 cup mild soap per gallon of lukewarm water) and rinse. Removing the dirt layer lets the bleach reach the growth.
- Apply the bleach solution. Mix 1 cup bleach and 1/4 cup mild soap in 1 gallon of water. Apply with a sponge or pump sprayer to the affected areas and a few inches beyond.
- Let it soak. Leave it about 15 minutes. Keep it damp; do not let it dry on the fabric.
- Scrub gently. Use light circular strokes with a soft brush. Repeat once for stubborn spots.
- Rinse thoroughly. Rinse until no bleach smell or suds remain. Pay attention to seams and hems, where residue collects and can degrade thread over time.
- Dry completely. Leave extended until fully dry, including the hem pockets and valance.
- Re-treat. Bleach removes the water-repellent finish. Apply a fluoropolymer fabric protector made for outdoor acrylic once the fabric is clean and dry.
Worked example
A 14 ft wide, 11 ft projection awning has 154 sq ft per face. Suppose mildew covers the outer 3 ft along the front edge on both faces: 14 x 3 = 42 sq ft per face, 84 sq ft total. At roughly 100 to 150 sq ft of coverage per gallon when brushing or spraying, 1 gallon of bleach solution (1 cup bleach, 1/4 cup soap) is enough, with a second gallon held back for a repeat pass on stubborn spots. Treating only the affected zone, rather than all 308 sq ft, limits how much repellent you strip and how much bleach runs onto plantings.
When stains remain after treatment
Sometimes the mold is gone but a shadow stays. That can be pigment left by the growth, or, on polyester and printed fabrics, dye damage. A second treatment a week later sometimes lightens it further. If a stain survives two careful treatments, accept it or plan for replacement; repeated bleaching shortens fabric and thread life.
Signs the mildew has caused real damage:
- The fabric tears easily when pinched and pulled at a stained spot.
- The coating on the back of polyester flakes or peels where growth was heaviest.
- Seam thread breaks or pulls apart near the affected area.
- A musty smell returns within days of treatment, suggesting growth inside a seam, hem pocket or the roll itself.
Thread is often the weak point. If seams are failing, see awning repair for re-stitching options; if the panel itself is compromised, replacing the awning fabric is usually the better investment.
How to prevent mildew
- Never store it wet. If you must retract in rain or wind, re-extend within 24 to 48 hours on a dry day and let it air out.
- Rinse regularly. A hose rinse every 2 to 4 weeks in season removes the pollen and dust that feed growth.
- Rinse soap away completely after every cleaning.
- Keep the pitch steep enough to drain, at least about 14 degrees, steeper in rainy climates.
- Trim overhanging branches to reduce sap, leaf litter and shade.
- Maintain the water repellent on acrylic, so water beads off instead of soaking in.
- Clean and dry before winter. Months of storage magnify any moisture trapped in the roll. Our winterizing guide covers end-of-season steps.
- Consider fabric choice at replacement time. In humid, shaded settings, solution-dyed acrylic or vinyl-coated fabrics resist mildew damage better than coated polyester. The fabric selector can help narrow options.
Pro tip: Motorized awnings with a rain sensor retract automatically when it rains, which protects the awning but also rolls it up wet. If you use one, build a habit (or a smart-home routine) of re-extending the awning on the next dry, calm afternoon.
When to call a professional
A professional clean, typically about $100 to $400, is worth it when growth covers most of the canopy, the awning is on a second storey, or the fabric is a commercial vinyl with printed graphics you do not want to risk. Professionals can also check whether moisture is coming from a failed seam or from water running off the roof onto the canopy, which no amount of cleaning will fix.
It is also worth calling in help if someone in the household has asthma or mold allergies; the EPA recommends that people with mold sensitivities avoid cleanup work themselves.
Frequently asked questions
Will bleach ruin my awning?
Diluted bleach is approved by major makers of solution-dyed acrylic for mildew removal, typically 1 cup bleach and 1/4 cup mild soap per gallon of water. It will strip the water-repellent finish, so re-treat afterward. On coated polyester, vinyl and printed fabrics, bleach can fade dyes and weaken coatings, so use a cleaner the manufacturer approves instead.
Does vinegar kill mildew on awnings?
White vinegar can help on light surface mildew and is sometimes used on fabrics that cannot take bleach. It is less reliable on established growth and should still be tested on a hidden spot first. Never combine vinegar with bleach, because mixing them releases chlorine gas. Rinse thoroughly afterward and check whether your fabric maker recommends against acids.
Why does mildew appear in stripes on my retractable awning?
Stripes usually match the wraps of fabric on the roller tube, which means the awning was retracted while damp. Moisture trapped between layers lets mildew grow along those lines. Treat the growth, then make a habit of extending the awning to dry fully after any rain, dew or cleaning before rolling it up again.
Can mildew come back after cleaning?
Yes, if the conditions that caused it remain. Mildew returns when fabric stays damp, dirt builds up or soap is left behind. Rinse the awning every few weeks in season, rinse thoroughly after cleaning, keep the pitch steep enough to drain, re-treat acrylic with water repellent and never store the canopy wet.
Is mildew on an awning a health risk?
Outdoor mildew on an awning is generally a cosmetic and fabric-durability issue, but mold spores can irritate people with allergies or asthma. Wear gloves and eye protection when cleaning and brush spores away from open windows. The EPA advises people with mold sensitivities or respiratory conditions to avoid doing mold cleanup themselves.
Sources and further reading
- U.S. Environmental Protection Agency: A Brief Guide to Mold, Moisture, and Your Home
- Sunbrella (Glen Raven): Cleaning and Care instructions, including mildew removal for Sunbrella fabrics
- Centers for Disease Control and Prevention: Mold, basic facts and cleanup guidance
- Professional Awning Manufacturers Association (PAMA): awning care resources
How we write our guides: figures are typical US ranges checked against manufacturer documentation, published standards and installer pricing. Read our editorial standards. Spotted an error or outdated detail? Request a correction.