Stain Identification & Removal Guide (with Photos)

Twenty-four stains we get asked about at the counter, each with a photo, what you are looking at, and what takes it off. Match the photo first. The wrong chemical on the wrong stain makes it worse, and a few of these are not stains at all: they are damage you need to photograph and point out before you start.

Four rules before any of this: test a small spot first; pre-wet and rinse plants; never mix acids with bleach; and if it says aluminum siding, believe it. Aluminum discolors with almost every chemical on this page.

Siding & Walls

Bat Droppings

Dark drips and spatter under eaves, vents and gable ends.

Fix: Pre-soak with Roof & House Wash and warm water, let it dwell, then rinse at low pressure.

Clear Deck Sealer Overspray

Blotchy, shiny or dirty-looking patches on siding next to a sealed deck.

Fix: On vinyl siding only: a mild mix of Rip It Deck Stain Remover, dwell, rinse. Do not attempt on aluminum siding.

Deck Stain Overspray

Brown or red speckles and drips on siding, trim and windows near a deck.

Fix: On vinyl siding only: Rip It Deck Stain Remover, dwell, rinse. Do not attempt on aluminum siding.

Rust Stains

Orange-brown streaks below nails, fasteners, well water sprinklers or metal fixtures.

Fix: A mild acid: Wood Britener, Brick Clean or F9 BARC / F9 Efflo. Rinse well and keep it off glass and metal.

Egg Stains

Yellow smears and dried drips, usually after Halloween.

Fix: Pre-soak the whole area with soap and warm water. Use Roof & House Wash without bleach, let it dwell on vinyl (not aluminum) and brush lightly with a soft bristle brush. Still there? Try white vinegar, then the house wash again.

Graffiti

Spray paint or marker on siding or masonry.

Fix: Worlds Best Graffiti Remover Bare Brick & Stone for vinyl siding and masonry. See the graffiti removers collection for other surfaces. Do not attempt on aluminum siding.

Paint Oxidation

Chalky white powder that comes off on your hand. Paint failing from UV.

Fix: Do not clean this with any pressure. Tell the customer the siding needs to be restored or replaced, and get a written OK that you are not responsible for discoloration before you touch it.

Melted Vinyl Siding

Rippled, warped panels, usually on one wall.

Fix: Caused by sun reflecting off nearby windows, or by a grill or running motor near the wall. Not a stain, cannot be cleaned off. Photograph it and tell the customer before you start.

Hail Damage

Small dents and half-moon marks in siding and gutters.

Fix: Cannot be fixed by cleaning. Photograph it and point it out before the job so it is not blamed on you.

Paint Run (Oxidation)

Streaks running down siding below a painted shutter or trim piece.

Fix: Someone painted the shutter and the paint oxidized and ran onto the siding. Remove with Worlds Best Graffiti Remover Bare Brick & Stone. Do not attempt on aluminum siding.

Mold & Mildew Spores

Small black spots, shown next to a pen for scale. New growth.

Fix: A standard house wash mix of 12.5% sodium hypochlorite and Roof & House Wash takes it off easily at this stage.

Thermal Bridging

Green or gray growth in evenly spaced vertical stripes on the wall.

Fix: The studs are warmer than the voids between them, so growth takes hold in the stud lines first. Normal house wash removes it; expect it to come back in the same pattern.

Water Drips

Brown vertical drip lines from the bottom of siding panels.

Fix: Water gets behind the overlap or in through weep holes and carries dirt out. Lightly mist the siding with soap, then rinse with a light mist.

Bad Window Seal

Fog, haze or streaks between the panes that will not wipe off.

Fix: Not dirt: the seal has failed. Photograph and notify the customer before cleaning so it is not blamed on the wash.

Masonry & Concrete

Efflorescence

White powdery bloom on brick, block or concrete. Disappears when wet, comes back when dry.

Fix: A mild acid: Brick Clean or F9 BARC / F9 Efflo. Do not seal until it is completely gone.

Mud & Clay Stains

Orange-red splash stains along the bottom of walls after heavy rain.

Fix: Mild acid: Brick Clean or F9 BARC / F9 Efflo.

Calcite Run

Hard white crust running down brick below a leak or joint.

Fix: Chisel off the heavy build-up, then treat repeatedly with an acid cleaner like Brick Clean or F9 BARC / F9 Efflo to dissolve the rest slowly.

Paint Oxidation on Brick

White haze on brick below aluminum siding or painted trim.

Fix: Oxidized paint ran down and stained the brick. Remove with Worlds Best Graffiti Remover Bare Brick & Stone or F9 BARC / F9 Efflo. Do not get the cleaner on the aluminum siding.

Oil Stains on Concrete

Dark blotches on a driveway or garage floor.

Fix: Kitty litter first: pick up as much oil as possible and grind it into the surface to pull more out. Then clean the concrete with F9 Double Eagle.

Roofs, Gutters & Decks

Gloeocapsa Magma (Roof Algae)

Black streaks on asphalt shingles, worst on the north side.

Fix: A bacteria-based algae that heats up the attic, raises A/C bills and damages shingles. Remove with a strong 4-6% mix of 12.5% sodium hypochlorite and Roof & House Wash. See the SH Mix Calculator.

Lichen & Moss

Green-gray patches and clumps on shingles.

Fix: Treat with a strong 12.5% sodium hypochlorite solution plus Roof & House Wash and leave it. It dies, dries and falls off with wind and rain. Do not scrub or pressure it off: the roots will tear granules out of the shingle.

Black Streaks on Gutters

Dark tiger-stripes on the outside face of gutters.

Fix: Dirt electrostatically bonded to the paint. House wash mix usually works; go stronger or use Powerhouse or a dedicated gutter cleaner if not. Apply soap to dry gutters and do not leave it on longer than 2 minutes.

Artillery Fungus

Tiny black dots the size of a pen tip, stuck hard to siding near mulch beds.

Fix: Artillery Fungus & Spore Remover. Apply it, cover with plastic wrap so it does not dry, and give it time. It is often better for the customer to do this themselves because it takes a long time. Do not attempt on aluminum siding.

Black Spots on Composite Decks

Scattered black specks across composite decking.

Fix: Two possible causes. Mold on the surface: regular house wash mix. Tannins bleeding up from the wood fibers inside the boards: a mild acid like Wood Britener.

Mix strengths and tools

Bleach ratios for house and roof mixes are on the SH Mix Calculator. Nozzle sizes for rinsing at the right pressure are on the Nozzle Chart. All the chemicals above are in pressure washing chemicals, and the counter will match a chemical to a photo if you text one to 301-519-9274.

Stain removal FAQ

  • Will bleach remove rust? No. Rust needs a mild acid. Bleach can set it.
  • Can I pressure wash oxidized paint? No. You will strip it unevenly and own the result. Get a written release first.
  • Why does moss come off the roof on its own? Because the SH kills it and wind and rain do the rest. Forcing it off pulls granules and shortens the roof.
  • What is safe on aluminum siding? Very little beyond a plain house wash mix. None of the strippers, acids or graffiti removers on this page.