You walk outside one morning, look up at your house, and think — wait, what is that? Green streaks, black spots, chalky white film, little dots that look like someone peppered your siding with a BB gun. Don't panic. Most of what's growing on your home is more common than you think — and a lot of it is very treatable with the right house washing approach. Here's what you're probably looking at, and what it means.
🧼 Stain Removal Difficulty — Quick Reference
The Most Common Types of Stains on Exterior Siding
Before we dig in — one important thing to know. Not every stain on your siding is fully removable, and an honest contractor will tell you that before the job starts, not after. Things like surface oxidation, artillery fungus, and deep rust stains can sometimes be improved but not eliminated entirely. At Simple Clean LLC, we make it a point to walk the property beforehand and flag anything that might not come off completely, so there are no surprises when the truck pulls away.
Now — let's talk about what might actually be on your house.
🌿 Dirt and Pollen
The most common culprit — and the most straightforward to deal with. Dirt and pollen cling to siding through wind, rain, and everyday activity. A big storm rolls through, kicks up dust and pollen, and suddenly your siding looks like it hasn't been touched in years. Landscaping work around the house? That stirs things up too.
The good news is that standard soft washing takes care of dirt and pollen easily. It's the bread and butter of an exterior cleaning service, and when done right, the results are immediate and satisfying.
☀️ Surface Oxidation
See a chalky white haze on your vinyl siding, especially on the sun-facing sides of your home? That's oxidation — and it's caused by years of UV exposure slowly breaking down the outer layer of your vinyl. It typically shows up somewhere between 5 and 10 years after installation, and it's more pronounced on areas that get direct sunlight all day. Shaded spots under soffits or eaves tend to hold up much better.
Wet your finger and rub it on a dry section of siding. If you see a chalky white residue on your fingertip, oxidation has set in. The more pronounced it is, the further along the process.
Oxidation is one of those stains where we'll always be upfront with you before we start. Specialty restoration cleaners can improve the appearance in some cases, but full removal depends on the age and condition of the material. We'd rather set accurate expectations than promise you something we can't deliver.
🟢 Algae
Algae is that green tint you'll often notice on the shaded, north-facing side of your home. It's believed to travel through the air from nearby bodies of water, lands on your siding, and starts feeding off the dirt and organic material already there. Left unchecked, it just keeps growing.
The good news? Algae responds really well to a proper soft wash treatment. It won't cause structural damage to your siding on its own, but the longer you let it sit, the more established it becomes — and the more it can work its way into gaps and seams. Staying on top of it with routine house washing is the simplest prevention.
⚫ Mold and Mildew
Mold and mildew are moisture-lovers. They thrive in areas that stay damp and don't get much direct sun — think the north side of your home, under overhangs, or behind shutters where airflow is limited. They can show up in a range of colors: white, gray, black, even yellowish.
Unlike algae, mold and mildew can pose actual health risks — especially if left to spread and get into your home's envelope. They also spread quickly, so this is one you don't want to let sit. A proper power washing treatment using the right sodium hypochlorite-based cleaning solution eliminates mold and mildew at the source — not just masking it on the surface.
🕷️ Cobwebs, Spiderwebs, and Bird Droppings
Nobody wants to talk about this one, but here we are. Spiders love corners, eaves, light fixtures, and any spot where they can set up shop undisturbed. And birds? Well, they go where they want.
The good news is that these are among the easiest things to clean off your home. A thorough exterior house washing takes care of cobwebs, spiderwebs, and bird droppings completely. Keeping your home's exterior regularly cleaned is also one of the best ways to discourage spiders from settling in — they prefer dark, undisturbed spots, and a freshly washed house doesn't give them much to work with.
🟤 Red Clay Staining
If you're in Pennsylvania, you've probably dealt with red clay. It's common throughout the region, and when heavy rain hits, that clay-rich runoff can work itself deep into the pores of concrete, brick, stucco, and foundation walls through splash-back. Red clay contains iron oxide — essentially rust — which makes it stubbornly insoluble and tough to remove once it's had time to set.
Depending on how deep the staining has penetrated and how long it's been there, a pressure washing treatment with appropriate chemistry can significantly improve the appearance. Results vary based on surface porosity and how long the stain has been setting — another reason timely cleaning makes a real difference.
🪨 Calcium and Efflorescence on Brick and Block
Those chalky white streaks or crusty deposits on brick and block walls? That's efflorescence — mineral salts (primarily calcium) that leach up through the masonry as water moves through it and then evaporates on the surface. It's not harmful to the structure, but it's not exactly a look anyone is going for either.
Treatment involves industry-standard cleaning solutions and appropriate water pressure to break down and flush out those mineral deposits. That said, total removal isn't always guaranteed — using too aggressive an approach risks damaging the masonry itself, which is a trade-off no one wants. And since the calcium is leaching from deposits within the masonry joints, it can come back over time. Sealing any cracks in mortar or brick is the best long-term prevention.
🔫 Artillery Fungus
Ah, artillery fungus. The one that makes homeowners' eyes go wide when they find it. If you're seeing tiny dark spots on your siding that look like someone peppered the wall with a fine spray of tar — that's it. You might also hear it called "shotgun spores," which gives you a pretty clear picture of how it spreads. The fungus lives in mulch, builds up pressure, and literally shoots spores into the air — right onto your siding, your car, your windows.
Artillery fungus spores are notoriously difficult to remove once they've bonded to siding. They have a sticky, root-like attachment just below the surface. Pressure washing can sometimes improve the appearance, but full removal is often not achievable without risking damage to the surface itself. We'll always be straight with you about what's realistic before we start.
The best prevention? Switch to cedar mulch or rubber mulch, which are far less hospitable to artillery fungus. If you use traditional wood mulch, turning it regularly can help disrupt the growing conditions these spores need.
🟠 Rust Stains
Rust stains on siding usually trace back to a specific source — an old light fixture, window unit air conditioner, rusty screws or nails, or metal hardware that's been slowly bleeding onto the surface below it. The streaks can range from faint orange to deep brown, and they tend to run vertically from wherever the rusting element is located.
The right chemicals and pressure washing technique can improve or remove rust staining — but here's the catch: if you don't address the source of the rust, it'll be back within weeks. Replacing corroded hardware, updating old fixtures, or sealing the source is just as important as cleaning the stain itself.
