To clean a Portland garage door, wash it with mild detergent, a soft brush and a garden hose, sand and prime rust spots in dry summer weather, and brush moss off by hand rather than pressure washing. Mildew comes off with the same soapy water and a soft brush.
The door needs that care because it spends a good part of the year damp. Its face takes wind-blown rain, its lowest few inches sit in splash and runoff, and a door on a shaded lot can stay wet for weeks at a stretch in winter.
This guide covers the outside of the door: washing it, catching rust early, and clearing green growth without wrecking the finish. If water is actually reaching the garage floor, start with our page on rain coming under the door, because that is a seal or slab problem rather than a cleaning one.
How wet the Portland year really is for a garage door
The Portland year is very wet from November through January and nearly dry in high summer, which makes summer the season to sand and paint and fall the season to clean.
By NOAA’s normals for the Portland airport, about 93 days a year bring at least a tenth of an inch of rain, a real soaking rather than a sprinkle. November, December and January each average measurable rain on 18 or 19 days.
July and August swing the other way, with measurable rain on fewer than four days in each. Primer and paint need dry days to cure, so that window suits rust repair and refinishing.
Shade stretches the wet season at the door. In Bridlemile, where trees cover about half the neighborhood, or on any lot with a big fir over the driveway, a north-facing door can stay damp long after the street has dried.
What you are looking at on your door
Orange freckles or bubbling paint near the bottom edge is rust, green film or black speckles are algae and mildew, fuzzy clumps are moss, and white crust on aluminum is oxidation.
| What you see | What it usually is | What to do |
|---|---|---|
| Orange freckles or a thin orange line at the lowest edge | Surface rust where the paint has worn through | Clean, sand lightly, prime and paint in dry weather |
| Paint bubbling or flaking in a band across the lowest section | Rust spreading under the paint film | Sand back to sound paint and bare metal, then prime |
| Holes, crumbling edges or soft metal at the bottom corners | Rust-through of the steel skin | Price a replacement bottom section |
| Orange streaks running down from hinges or brackets | Rusting hardware bleeding onto the face | Wash the streaks off and have the hardware checked |
| Green film on the side that never sees sun | Algae or mildew on a surface that stays damp | Wash with detergent and a soft brush |
| Black or gray speckles that smear when wiped | Mildew | Wash, rinse and let it dry fully |
| Fuzzy green clumps along the base or the trim | Moss holding water against the door | Brush off by hand, then fix what keeps it wet |
| White chalky crust on an aluminum door | Oxidized aluminum, not rust | Wash; repaint later if the finish is thin |
How to wash a garage door without hurting the finish
Use a bucket of warm water with mild household detergent, a soft brush or sponge and a garden hose, working from the top down.
- Pick a mild, cloudy day. Soap dries in streaks in direct sun, and an overcast afternoon gives you time to rinse.
- Rinse first. Wet the whole door with the hose to loosen grit, paying extra attention to the lowest few inches, where it collects.
- Wash one section at a time. Work the soapy sponge or brush across each section from the top down, so dirty water runs over panels you have not cleaned yet.
- Open the door a foot and wash underneath. The underside of the bottom section and the seal retainer hide silt, leaves and salt.
- Rinse thoroughly. Soap film left on the paint holds dirt and keeps the surface damp longer.
- Clear the slab. Push standing water away from the door with a squeegee or broom so it does not sit against the bottom seal.
Amarr’s care guide calls for washing the outside of a door once a year, more often where salt reaches it, and it says not to pressure wash at all. A pressure wand can drive water behind trim and into the seams between sections, lift paint at the edges, and tear a rubber weatherseal.
Treating rust on the bottom section
Surface rust caught early is a weekend job: clean it, sand to bright metal, prime with a rust-inhibiting primer and repaint, all before the fall rain returns.
Steel door skins depend on their factory finish, paint over a protective coating, to keep rust away. Once a shovel scrape, a bike pedal or years of splash wear through both layers, the bare steel starts to rust, and the rust creeps sideways under the paint around it.
Sand with fine sandpaper or a sanding sponge rather than a wire wheel, and stop where the paint is sound. Wipe off the dust, spot prime the bare metal with a primer labeled for rusty or galvanized steel, then apply two thin coats of exterior paint in the door’s color.
If the door is young enough to still carry its maker’s warranty, photograph the rust and read the terms before sanding anything. Coverage varies from maker to maker, and you want to know what a claim requires while the damage is still visible.
Rust-through is a different story. When the steel is perforated, or the bottom edge flakes away in layers, paint has nothing left to grip. The usual answer is a matching replacement bottom section, or a new door when the model has been discontinued.
Rust on springs, cables and brackets is a different problem
Rust on the parts that carry the door’s weight is a safety issue rather than a cosmetic one, and it belongs to a technician instead of a sanding sponge.
The cables that raise the door are anchored to brackets at the base of the bottom section, in the wettest corner of the garage. A cable with rust-colored or broken strands near the bracket can snap and drop one side of the door, and the bracket itself is under spring tension, so it should never be loosened. Frayed or rusty cables call for cable and drum repair.
Torsion springs show rust as an orange crust on the coils. Wiping the coils with a little door lubricant every autumn slows it down, and a spring already scaly with rust is worth having looked at during a tune-up.
Getting rid of mildew and moss
Scrub mildew off with detergent and water and brush moss away by hand, then deal with the dampness that let them grow, or they will be back by spring.
The EPA’s guide to mold and moisture makes the same point for any hard surface: the key to mold control is moisture control, and cleanup means detergent, water and complete drying. It does not recommend chlorine bleach as a routine cleaner, and it warns against ever mixing bleach with ammonia.
Moss settles where water lingers: the base of the door, the trim beside it and the seam where the driveway meets the slab. Lift it off with a stiff nylon brush, never a metal scraper, and rinse. If a moss product will be used anywhere near the door, check its label for painted metal or wood first.
Then take away the reason it grew. Trim shrubs that keep the door in constant shade, turn downspouts away from the driveway, and make sure the bottom seal and threshold shed water instead of holding a puddle against the door.
Wood doors need gentler handling. Use the same mild soap and soft brush, skip anything abrasive, and look closely at dark patches near the bottom rail: soft, spongy wood under the mildew is rot, and our guide to rot in wood doors explains what to do about it.
A twice-a-year routine that keeps rust and moss in check
Two sessions a year keep a door ahead of rust and moss: one in late spring, when paint can cure, and one in early fall, ahead of the November rain.
- Late spring: wash the door, inspect the bottom section, and sand, prime and paint any bare spots while the weather stays dry.
- Early fall: wash again, clear moss and leaves from the base and the tracks, lubricate hinges and springs, and confirm the bottom seal still meets the floor along its length.
- After any icy morning with ice melt on the driveway: hose the bottom section and seal with plain water. Our ice storm prep guide covers the rest of winter at the door.
If rust has reached the hardware, or has eaten holes in the lowest section, text a picture of the worst spots. We will tell you whether the door needs a new section, a new seal or just a sanding block.