The Rainbow Of Vinyl Siding Stains: What They Are And What To Do About Them

Even though vinyl siding is largely maintenance-free, it can occasionally develop unsightly stains. Some stains are easy to get rid of permanently, while others can recur until the source of the problem is eliminated. Here are some common, different colored siding stains, their causes and what to do about them.

Runny, Sticky and Brown

These sticky, resin-like stains are a mixture of moisture and oil in wood. They are usually the result of ice dams on the roof. When the ice melts, the water seeps through the roof, into the wood sheathing and out through the spaces between siding strips. On its way out, it picks up the naturally-occurring oil in the wood. It is more common in older homes with cedar sheathing because cedar contains more oil than most woods. However, it can also happen in new homes with particle board sheathing.

These stains can usually be removed by power washing once winter is over and ice no longer forms. However, they will probably recur unless you address the moisture level in your home, which is what causes the ice buildup.

Dry and Reddish-Brown

These dry, powdery stains result from a combination of moisture and improper fasteners on the plastic house wrap underneath the siding. This wrap is intended to create a barrier against water penetrating the siding and damaging the wood underneath, while allowing moisture to escape. Unfortunately, the quality of wrap varies and sometimes moisture becomes trapped. If the contractor did not use nails with plastic caps, the moisture can make the nails rust. When the moisture picks up rust particles as it seeps out, it deposits a red stain.

These stains can be removed with a power washer or with a household rust-removing cleanser and a soft-bristled brush. However, in extreme cases you may need to replace the nails with rust-resistant ones or replace poor-performing wrap with felt to eliminate moisture buildup.

Vertical White Streaks

These streaks are known as ghosting, and also results from condensation caused by temperature differences between the wall studs and the insulated parts of the wall. Studs are cooler, so the siding on top of them forms more condensation. The white streaks are an accumulation of pollen, pollution and other particles in the air. It is more common on the side of the house that receives the most sun.

These streaks can be removed with household detergent. However, too much buildup can damage the siding, so you may need a professional to investigate why there is so much heat variation underneath the siding and address the cause.

Sticky, Black Speckles

These hard-to-remove dots are not caused by a problem with the siding installation or moisture buildup. They are the spores of Sphaerobolus stellatus, otherwise known artillery fungus.  This fungus grows in decomposing mulch and shoots its spores onto nearby surfaces. It is difficult to remove by power washing or with ordinary cleaners. Each speck needs to be gently scraped away within 2 to 3 weeks or it will permanently dry in place. You should also dispose of any finely shredded wood mulch – its favorite breeding ground -- with bark mulch or a drier material. Sometimes the only solution is to replace or paint the affected siding.

These are a few of the most common stains on vinyl siding. For the best advice on removing these stains without damaging the vinyl, contact a professional siding contractor. Not only do they know the best way to restore siding, but they can also determine if it was improperly installed or if there are other issues that need to be fixed to keep the stains from returning.


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