Q&A on vinyl siding stain causes, cures, cleaning procedures, chemicals, products:

This article series discusses common causes of stains or discoloration found on vinyl building siding.

Distinguishing the type of stain found on siding is useful in deciding on the cause and thus the cure or prevention of staining

FAQs on How to Clean or Remove Stains on Vinyl Siding

These vinyl siding stains and vinyl siding cleaning diagnostic questions & replies were posted originally at VINYL SIDING STAINS - so you will want to read the stain diagnosis and advice given there.

On 2023-01-12 by InspectApedia Publisher (mod)

@K,

Apologies, I owe you both an answer, but honestly we are flying more blind than a bat with these questions. We know nothing about the siding material age, wear, exposure, weathering, , building construction, age, conditions, climate, etc.

When you wiped the siding what cleaner or chemical was used?

What is the siding material: painted wood, vinyl, metal, shingles, cedar, pine, fiber cement, asbestos cement?

It sounds as if we're talking about wood shingles but I just don't know.

How was the surface treated?

Fire retardant treatments generally don't impart a color to wood except perhaps to slightly darken it.

Try gentle washing with dish soap - that can dissolve the oily mineral spirits.

On 2023-01-12 by K - stains on blue vinyl siding

@Anonymous, did you ever get an answer? We have this same problem and also have blue vinyl siding!

On 2020-09-05 - by (mod) - what's this drippy stain on my vinyl siding?

Apologies, Susie, for the delay in approving your photo;

When a reader posts a comment that includes a photo or a link she sees a message (missed by some readers) that the comment or posting or image will appear AFTER it has been reviewed and approved by the system moderator. This protects our website and readers from spam, viruses, and from inappropriate content.

Look above the stain point for a drip source above the point on the siding where you see this stain, perhaps at a window or an insect nest.

Sometimes we also see these drip stains just below the small vent openings cut into the bottom edge of vinyl siding.

In that case moisture or wind-blown rain penetrated the siding and dissolved colorants in the building dust, dirt, or on its sheathing below the siding itself.

On 2020-09-02 by Susie - gooey stuffs on my grey vinyl sidings

Hi, I have noticed gooey stuffs on my grey vinyl sidings recently. It Is only on one side Of the house facing northwest, lower part. I cleaned them up with bleach but appeared again. What they could be? Very strange. It doesn’t appear to be coming from the inside of the siding. Please see attached picture

[Multiple posts by same reader: - Ed.]

Hi there is gooey stuff appeared on my grey vinyl siding recently, it’s only on the northwest side of the house, lower level. I cleaned with bleach but they reappeared again. It is not from inside or behind of the siding, please see picture. What could this be? Thank you

Hi, I recently noticed gooey stuff on my grey vinyl siding. It’s only on the northwest side of the house, lower level. I cleaned them with bleach but they reappeared. See picture. What could it be? It’s not coming from behind or inside the siding. Thank you

Hi, I saw some gooey stuff on my siding recently and it reappeared after I cleaned it. It is not from behind or inside the siding. I can’t seem to attach picture here.

What is the gooey stuff on my siding could be? I can’t attach picture here, or it won’t post

On 2020-08-31 - by (mod) - oozing black stain leaching out of a roofing strut constructed of azek.

Marni that sure looks like a leak from above. I'd look up from that point, observing the roof and soffit closely for leaks. Also look for heated oozing roofing mastic sealant such as near a chimney or plumbing vent flashing.

On 2020-08-23 1 by Marni

Hi there. I have an oozing black stain leaching out of a roofing strut constructed of azek.
I suspected a wasp nest, but cannot find an entry hole. Nor do I hear any buzzing. Here is a picture of the main stain.

On 2020-04-18 - by (mod) - White dots (dime size) are appearing in vertical lines all over the siding.

I don't know, Jim. We'd need more information to hazard a guess. Perhaps you can

- attach a photo of the white dots - sharp closeup

- attach a photo fo the wall from a more-distant point

- give country, city, of installation and

- siding age

- weather conditions: is this in freezing weather?

- and note if the white dots are on all building sides or just some and if just some, which sides vs which exposure to sun, shade, etc.

On 2020-04-18 by Jim Gately

Have grey vinyl Georgia Pacific siding. White dots (dime size) are appearing in vertical lines all over the siding. What is causing this???

On 2020-04-04 - by (mod) - oily streaks on my vinyl siding

Way to go, Steve.

And thanks for posting the follow-up. It will doubtless help other readers who are tracking down mysterious oily stains on siding.

If you can, please use the "add image" button to show us your oily siding.

On 2020-04-04 by Steve

Actually, never mind about my question below. I just remembered I sprayed WD-40 the other day around the interior of the window frames to make them open and close more easily. It worked, but some of it must have drained down on the exterior walls.

I notice there are oily streaks on my vinyl siding under all the windows on my house, on all sides. They range from 4-5 inches to a foot wide, and from a few inches to 3 feet top to bottom. The streaks are oily/greasy to the touch, but they are clear and shiny, not discolored.

It's only the shine that makes them stand out from the rest of the vinyl. They're all below the left and right edges of the windows, not the middle of the windows.

Some start directly below the window edges, and some start a few inches below. What could be causing this? We've had a very rainy winter/spring, but I don't know what that might have to do with it. There are no animals/nests around the windows and no streaks above them or beside them, only below.

On 2019-05-30 - by (mod) - blue spots all over the siding.

Take some sharp photos both close up and we're just didn't to give context and post those here. Use the add image button to post one photo per comment. That might allow us to make more specific suggestions.

But certainly it's the case that there are fungi or molds and algae of a great range of color. Never just black.

On 2019-05-30 by Jerry Myers

We live on lake huron. We have blue spots all over the siding.
Everything I have read so far has been black spots.
Any ideas?

On 2019-02-05 - by (mod) - green "mold" or what ever it is on the side of my home-

Could be mold or algae or something else. Usually shade and moisture are factors.

Air leaks or moisture leaks from inside into the wall cavity would not easily explain deposits on the exterior surface of the siding, though like you I don't fully rule that out.

Perhaps you can add an image or two.

On 2019-02-05 by elizabeth Speakman

I have the green "mold" or what ever it is on the side of my home---a new part was built on to a wood sided home.

The original home never had any of this. Now it is mainly on the new part but ALL the home was done in new vinyl siding. This did not happened for about three years and now is getting worse.

It is totally on the two sides with no shade, plenty of sun and wind but happens in the winter more so. I am finding some things the contractor did do right and was wondering if he put insulation under it or cheap, inferior type. What can I do to prevent this, tired of scrubbing the side of my home. thank you.

On 2019-02-05 by (mod) - green mold or something on my siding

Could be mold or algae or something else. Usually shade and moisture are factors.

Air leaks or moisture leaks from inside into the wall cavity would not easily explain deposits on the exterior surface of the siding, though like you I don't fully rule that out.

Perhaps you can add an image or two.

On 2019-02-05 by elizabeth Speakman

I have the green "mold" or what ever it is on the side of my home---a new part was built on to a wood sided home. The original home never had any of this. Now it is mainly on the new part but ALL the home was done in new vinyl siding.

This did not happened for about three years and now is getting worse. It is totally on the two sides with no shade, plenty of sun and wind but happens in the winter more so. I am finding some things the contractor did do right and was wondering if he put insulation under it or cheap, inferior type.

What can I do to prevent this, tired of scrubbing the side of my home. thank you.

On 2018-10-16 by (mod) - very moldy and algae-covered building siding - probably wood not vinyl

Your siding looks like wood, not vinyl.

The green material is probably algae.

The dark material may be algae or a fungus - perhaps Stemonitis sp. that likes to grow on wet wood, plywood, or OSB sheathing.

See VINYL SIDING STAIN CLEANING METHODS

You also most likely need to

Fix air conditioner condensate that runs down the building wall

Trim back trees to get more sun on the siding

Investigate the wall cavity in the areas of mold growth since there's a chance that water has penetrated the walls, inviting more-serious mold contamination, rot, insect damage.

On 2018-10-15 by nanab.isno.1

Are these some sort of mold spores or seeds growing where they stuck to the siding due to the ac window unit?

Is any of this possibly dangerous?

How do we need to get rid of it & how do we need to clean the ac window unit?

On 2018-08-25 by InspectApedia Publisher (mod) - how to get mineral spirits stains off of my siding

@Todd Rzepka,

Try gentle washing with dish soap - that can dissolve the oily mineral spirits

On 2018-08-25 by Todd Rzepka

I got mineral spirits on vinyl siding and it left dark marks. Any suggestions to remove?

On 2018-06-28 by (mod) - dark vertical streaks down new house vinyl siding

Kim

You could be right- water behind the siding dissolving asphalt and leaking back out at siding vents.

See if the stains originate at the small vent holes at the bottom of siding sections.

On 2018-06-27 by Kim - vertical stains on new house

Help! We built a new house and. Our siding looks terrible. It has always had these dark colour steak marks.

After a professional cleaning they still look dirty.
We suspect it’s the sub par tar paper our builder used instead of Tyvek.

The installers gave a couple of weak reasons for it and probably not going to warranty it. Mostly I just want to know how to fix it. Please help!!

On 2018-05-17 by (mod) -

It would help to see photos of the stain and to have an idea what comprises it: oxidized aluminum, paint, flag dye, something else.

Typically people try a diluted vinyl siding cleaner or TSP substitute in a small unobtrusive area first. If the siding is old and oxidized I'm not optimistic.

On 2018-05-17 by Jackie

Aluminum flag pole bled stain down vinyl siding -,how remove

On 2018-04-03 by (mod) - black deposits or stains on vinyl siding around gable end vent and windows

That looks to me as if the stains are from air leaks OUT of the structure either through or around the windows, similar to the exhaust air stains around the gable end vent.

On 2018-03-25 by Jim

I'm not sure if this is just dust and first gathering from air intrusion or if something else is going on.

This is the North side of the house. The house gets pummeled by the wind on this side. The siding is vinyl over celotex.

The roof is shingle over paper and 6 years old. There's another gable vent on the other side and a ridge vent that was installed when the roof was done. Any help would be greatly appreciated.

On 2017-12-08 by Anonymous - pink color when wiped - trouble cleaning siding

blue siding .. any idea what the issue would be the pink color when wiped looks like a clay color ( we have been wondering if its fire retardant ) as there were water bombing in our area or is it soot that has compromised the siding ? any comments

I have an 8 year old home with blue vinyl siding on it. House was in a major disaster wildfire over a year ago. Many houses in our area city were burned to the ground ... thankfully ours survived.

WE had it pressure washed after a year as we had no knowledge the it was suppose to cleaned as insurance never admitted that.

We had professional steam washer clean the house but after doing 2 sides of the house realized that there was something not coming of the siding. a residue that when you wipe it with a towel it is pink. tired 2 different cleaning solutions wit 2 different companies and the fi is still all over the house.

On 2017-06-24 by Anonymous - typical siding wash formula

Siding wash is typical water/bleach mix with recommended amt. of Zinsser Jomax thrown in.

On 2017-06-24 by Johnny Vinylguy

I have a vinyl-sided ranch that rarely needs power washing, especially the front, which faces the South/southeast.

But there is one window that always has a dark, mildewy patch above it, extending maybe 2 feet high. What could be causing the dark patch? No other windows in front have this condition over them. Thanks.

On 2017-05-25 by (mod) - pressure washing my siding turned it dark purple

Siding

Can you tell me what chemical was used in the siding wash? Here are some common siding cleaner chemical ingredient examples based on looking at the MSDS sheet for the product. When you tell me what cleaner was used we can understand its properties.

If portions of the siding are discolored even after drying completely there can be various causes, not all of which would be the fault of the cleaner nor cleaning process.

Siding cleaning mistakes and their causes are discussed in detail

at VINYL SIDING CLEANING METHODS

On 2017-05-25 by siding girl

I had my home pressure washed and on some parts of the vinyl siding it turned a dark purple color, same chemicals was used on all of the house and only one are changed colors. what could that be from?

On 2017-02-16 by (mod) - Pink stains on siding could be mold but more-often an algae.

Pink stains on siding could be mold but more-often an algae. Mold and algae both produce growths in a very large range of colours.

A repair might indeed make siding colors different on a building, but the color difference would be uniform within an individual piece of siding up against another; stains from algae or mold will have irregular edges and patterns and will usually match shaded or damp areas of the walls.

On 2017-02-16 by Susan

I have recently moved into a home built in 1947 with white siding on the garage and kitchenette.

Some parts of the white siding look pink! Friends have said it's probably mold but I thought mold was black/greenish. Around the back of the garage the first 5 panels are pink and all the lower panels are white.

Do you think at some point someone repaired the siding with two different types of panels?

On 2016-10-28 by (mod) - Typically algae forms on siding in shade and where it's damp

Typically algae forms on siding in shade and where it's damp.

You can power-wash but watch out for some inexperienced worker who blows water into the building walls by careless power washer aim.

On 2016-10-27 by Jessie - green algae forming on the siding on the side of the house and brown stuff on the front

My siding is not over five years old and within the last year or two I noticed green algae forming on the siding on the side of the house and brown stuff on the front of the house.

Not sure what is causing this and should I have the areas affected by the algae power washed?

On 2016-09-20 by Rachelle - black growth appeared over night on my siding.

This unknown black growth appeared over night on my siding. Starts off yellow then black when I removed it it was like brown dust & hairy. What is this.

Question: how can I remove the spots left on my siding after I had it cleaned?

Just sent you an e mail about my problem and this is the follow up pictures. We will have to reside our entire house if this issue is not solved as it is right by our doorbell and front door and it extensive in this area.

I would really appreciate your ideas as to the caused. I have contacted the company to have it cleaned again and it did not change. ... Anonymous by private email 2017/06/10

Reply:

I can't say for sure what the problem is with the yellowish stains I see on white vertical trim and darker stains I see on grey-beige vinyl siding in your photo. I suspect that a cleaner containing a bleaching agent may have been sprayed or over-sprayed onto a surface while working nearby, then let sit too long without actual washing-off.

Your question prompted me to prepare a researched answer in some detail that I hope will be useful and that I'll publish

at VINYL SIDING CLEANING METHODS

On 2017-05-25 by (mod) re: what are the common chemicals found in siding cleaners & how might using a cleaner leave new stains or marks on vinyl siding?

Siding

Can you tell me what chemical was used in the siding wash? Here are some common siding cleaner chemical ingredient examples based on looking at the MSDS sheet for the product. When you tell me what cleaner was used we can understand its properties.

If portions of the siding are discolored even after drying completely there can be various causes, not all of which would be the fault of the cleaner nor cleaning process.

See VINYL SIDING CLEANING METHODS for an explanation of why using a cleaner on vinyl siding may result in new spots or streaks on the wall or trim surfaces.

On 2017-05-25 by siding girl

I had my home pressure washed and on some parts of the vinyl siding it turned a dark purple color, same chemicals was used on all of the house and only one are changed colors. what could that be from?

On 2017-02-16 by (mod) re: pink stains on siding

Pink stains on siding could be mold but more-often an algae. Mold and algae both produce growths in a very large range of colours.

A repair might indeed make siding colors different on a building, but the color difference would be uniform within an individual piece of siding up against another; stains from algae or mold will have irregular edges and patterns and will usually match shaded or damp areas of the walls.

On 2017-02-16 by Susan

I have recently moved into a home built in 1947 with white siding on the garage and kitchenette. Some parts of the white siding look pink! Friends have said it's probably mold but I thought mold was black/greenish.

Around the back of the garage the first 5 panels are pink and all the lower panels are white. Do you think at some point someone repaired the siding with two different types of panels?

On 2016-10-28 by (mod) re: algae stains on siding: causes

Typically algae forms on siding in shade and where it's damp.

You can power-wash but watch out for some inexperienced worker who blows water into the building walls by careless power washer aim.

On 2016-10-27 by Jessie

My siding is not over five years old and within the last year or two I noticed green algae forming on the siding on the side of the house and brown stuff on the front of the house. Not sure what is causing this and should I have the areas affected by the algae power washed?

On 2016-10-28 by (mod) re: what is the yellow and black stuff on my vinyl siding?

I can't know from just your e-text Rachelle, but common yellow stuff on siding is pollen and black stuff may be dirt, road dust, algae, mold. If it's actually hairy and not a leftover from vines growing on the surface I suspect it's a mold growth or a dried out algae or moss.

When such stains appear suddenly I'm baffled too but would look for a source of mold growth, artillery fungs, or from an event that could have left soot such as a nearby fire.

On 2016-09-20 by Rachelle

This unknown black growth appeared over night on my siding. Starts off yellow then black when I removed it it was like brown dust & hairy. What is this.

...

Continue reading at VINYL SIDING CLEANING METHODS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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