Types of Stains on Siding

December 26, 2022

What is Growing on my House!?

If you notice that your home siding is looking discolored, don't panic. It's fairly common, especially if you don't regularly maintain your house. There are a few different types of discoloration, and in this blog post we'll cover the most common ones.  Conventional power washing services may not be enough to remove certain types of stains, such as surface oxidation, artillery fungus, or rust stains. If there are any oxidized caulk drips around windows, oxidized siding powder, metal oxide drips from metals, or stripes on gutters, we will attempt to point these areas out to the customer before beginning the project. However, sometimes these stains cannot be removed at all. There is a possibility that some restoration cleaners may be able to remove certain stains from certain surfaces. However, this is not always the case, as it depends on the material, the age of the material, and how worn it is. For example, you would not be able to wash a car that has been sitting in the sun for 20 years and expect it to look like it just came off the factory floor.

Different Types of Stains on Exterior Siding 

Dirt and Pollen Dusting

Dirt and pollen are the most common types of stains you'll see on the outside of your home. They attach to your siding in a variety of ways, some of which are caused by elements like rain and wind. For example, if there's a big storm with high winds, loose dirt, pollen, and even mud can be blown through the air and end up on your home. Or you can create dust that ends up on your siding while you're doing things like landscaping around your house. Either way, it's important to know how to remove these stains so your home always looks its best. 

Surface Oxidation

Vinyl siding oxidation is caused by the sun's UV rays and is typically visible after 5-10 years. If you're not sure if your home's siding is affected, try this test: wet your finger and rub it on a dry area of the siding. If you see any chalkiness or whiteness on your finger, then your siding has started or is well along in the oxidation process. If you notice a white haze on your vinyl, it's because the sun has bleached it and caused damage. This is more prevalent in areas that are exposed to direct sunlight, like porches or behind shutters. However, if you look at vinyl in shady areas or under soffits and eaves, you'll find that it's much less damaged because it hasn't been hit by the sun's harmful UV rays. 

Algae

Algae growth on home siding is a common issue that many homeowners face. Algae is typically found on the north side of the house, and can be identified by its green color. While the exact cause of algae growth on siding is not always clear, it is believed to come from bodies of water. If you are dealing with algae growth on your home, there are a few things you can do to remove it. If you don't power wash your siding, algae will be able to feed and grow on it. Once it gets airborne, it will attach itself to your siding and start feeding off the dirt. Algae won't cause any structural damage, but it can get into your siding if you don't take care of it. 

Mold and Mildew

Mold and mildew can be a problem for houses with siding, but there's no need to worry. These growths are caused by moisture build-up, which is more likely to happen in areas of the house that don't get direct sunlight. However, mold and mildew can be prevented with some simple tips. By taking care of your house and keeping it clean, you can avoid these problems altogether. Mold, mildew, and algae are all fungi that feed off of dirt and grime on your home's exterior. They can range in color from white to black or yellow, and they can pose serious health risks if not removed promptly. Mold and mildew should be power washed due to their ability to spread quickly. 

Cobwebs, Spiderwebs and Bird Droppings

No one likes finding spiderwebs, cobwebs and bird droppings on the side of their house. But when you live in an area with a lot of creepy crawlers and obnoxious hawks, it's just something you have to deal with. If you're finding that your home is constantly being covered in cobwebs, there are a few things you can do to try and deter the spiders from spinning their webs there. First, make sure you're regularly cleaning the area. Spiders are attracted to places that are dark and cluttered, so keeping the area around your home clean will help discourage them from setting up shop there. You can also try spraying the area with a spider repellent or setting up a spider trap. As for the birds, unfortunately there’s not much you can do about any of them. 

Red Clay Staining

Red clay is a type of soil that is most commonly found in the southern United States. However, it can also be found in other parts of the country, such as Pennsylvania and even some western states. Red clay stains typically occur after heavy rains, when water carries the clay deep into the pores of concrete, brick or stucco. Home foundation walls are often susceptible to this via splash build-up, but even the simple act of walking on a concrete driveway with muddy shoes can cause damage. Red clay contains iron oxide, which is better known as rust. This makes it highly insoluble, which is why it can be so difficult to clean red clay stains from concrete and masonry. 

Calcium and Efflorescence Staining on Brick and Block Walls

Calcium and efflorescence staining can be unsightly and difficult to remove. These stains occur when calcium and other minerals leach from mortar or bricks. Though the stains are not harmful, they can be difficult to remove. For removal, industry standard chemicals and appropriate water pressure will be used; however, total removal is not guaranteed as it would risk severe damage to the exterior building material. Over time, the stains may reappear because they are leaching from calcium chloride deposits in the masonry joints. To prevent calcium and efflorescence staining, make sure cracks or holes in mortar or bricks are sealed and keep the area around your brick and block walls clean. 

Artillery Fungus

If you notice tiny black spots on your house, it could be a fungus called artillery fungus. These fungi typically grow in perfect circles. If you try to scrape them off with your fingernail, you'll find that there's a layer of roots just under the surface. Another name for this fungus is "shotgun spores." The reason for this name is because of the way the fungi spread themselves. Artillery fungus is present in mulch. Homeowners who don't use mulch very rarely have any problems with artillery fungus. If they do, it's probably because of their neighbors' mulch. How can that be? The reason is that these spores spread by shooting themselves up into the air. 

Rust Stains

Rust stains can be removed with the appropriate chemicals and pressure washing. However, if the cause of the rust stain is not addressed (i.e. rusting hardware, metal elements, etc.), the stain can reappear quickly. Old electrical lights and boxes, Window Unit Air Conditioners, rusty screw and nails are common causes of Rust Streaks and Stains on the exterior surfaces of your home. 

Well, not only does Simple Clean LLC Power Washing Services have the vast experience to give your property a quality clean, but they can do so without damaging any building materials. Plus, they are always safety conscious. So why wouldn't you want to choose a company can trust?
Avoid the hassle and let us help provide you with a simple power washing service done right.  Contact us  today for a free estimate. 

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About the Author: Ryan McGowan

Ryan McGowan is the owner-operator of Simple Clean LLC Power Washing Services and brings 18+ years of real, hands-on experience to every project. Since founding Simple Clean in 2017, Ryan has built a reputation across Delaware County, Chester County, and surrounding areas for safe cleaning, consistent results, and straightforward communication. His approach blends field-tested skill with formal leadership training—so clients get both craftsmanship and professionalism from start to finish.


  • Owner-operator leadership: Ryan personally oversees jobs to ensure quality control, safety, and a clean finish
  • Local expertise: Serves homes and businesses throughout Delaware County, Chester County, and nearby communities
  • Built on honesty, reliability, and long-term customer trust
  • Certified with the Power Washers of North America: Certified in House Washing, Roof Cleaning, and Fundamentals of Power Washing
  • Safety-first credentials: Training includes OSHA 1910, DOT, EPA environmental compliance, GHS/HazCom, ladder safety, chemical safety, and first aid
  • Verified & accountable: AskTheSeal accredited for verified licensing and background checks
  • Industry leadership: Serves on the PWNA Board of Directors and contributes to the Marketing Committee, supporting higher standards across the trade
  • Wide service experience: From house washing and roof cleaning to driveways, patios, and commercial exteriors
  • Proof in the reviews: Backed by 200+ five-star reviews on Google, Facebook, and NiceJob
  • Client experience matters: Clear expectations, respectful service, and results that protect curb appeal—and the surfaces underneath it


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