Funk/soot/? coming from bathroom vent

Just wondering if you all know what this is? It is coming out of an upstairs bathroom vent. Looks like soot. I had a similar but much, much smaller patch on another house this year and HW didn’t touch it. That homeowner didn’t care, but this is the main point for this home. He swears it is from his wife’s hairspray?? The siding is not oxidized to I am not worried about product very much. He called me over from another house and didn’t have my extension ladder to get up there so I figured I’d get some opinions first. The bare area under the vent actually looks lighter than the rest of the siding. I appreciate your thoughts.

Would also like to get prevention strategies to offer up to him. The home is only 4-6 years old.

Prevention strategy, stop using the vent. Actual solution, tell him you can clean that side of the house every time it gets dirty for some $$… I dont know what it is but if your hw mix wont touch it with some brushing, im sure a degreaser would take care of it

Just dealt with the exact same thing this week. HW mix took care of it, easy peasy. The vent is doing its job, that area of siding gets a lot of moisture from the bathroom.


What is your degreaser of choice @AAPressurewashing00?

Appreciate it Jake, hope it will, I just want to have back up in the arsenal in case it doesn’t.

It’s likely organic which HW mix will take care of. That vent is probably from a bathroom or dryer which emits warm, moist air which is a great breeding ground for mold, mildew and algae.


I dont use a lot of degreaser I know a lot of people will use EBC for a wide variety of cleaning. I keep a bottle of purple power with me and some extra sodium hydroxide beads if I need to make it stronger and I have some bd-200 from Southside equipment. Really any would do you fine

Yup, housewash mix takes care of that quick. Did a house last month with it and homeowner was shocked.

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Thanks all for the replies. @AAPressurewashing00, do you cut yours down? I know it is concentrate. I have BC cleansol and have recently been reading about EBC. I will probably pick up a bottle or get some PP to have on hand.

I once mistook my test spot bottle of sodium hydroxide for my bottle of SH and discolored the siding. Thankfully it came off/back as I quickly rinsed it, but I haven’t heard of putting that on vinyl before.

I’ve cleaned a lot of houses that look just like that. My HW mix easily take if off every time. I think it’s just excess organic growth due to all the moisture coming from the vent.

What does your HW mix consist of?

I downstream to around 1% SH and use Apple Wash surfactant.

one vent is the dryer the other is likely the exhaust fan for the bathroom. I hate that cheesiness of those vents, there is a small vinyl hood that can go over those vents. example of one type

It annoys me as much as plumbers running vent pipes through the roof and not capping them. Everyone cuts corners nowadays, it is nice to see a finished house every once in awhile.

It’s mold. If you ever plan on scrubbing siding with degreaser, plan on scrubbing the entire side of the house to even it out if there’s any sign of oxidation.


Just curious why you think a vent pipe needs a cap? Even in a downpour only a small amount of water will get it and it just goes into the drain.

depends on your vent stack really, and some vent pipes that you see on roofs aren’t for plumbing. If you have a larger opening more water get in in a downpour. My brother doesn’t think much of it, and he is a professional plumber. Of course he doesn’t go out and remove a vent stack unless there is an issue. We have had this argument before, he doesn’t cap them unless specified in the build. On the million plus homes it is almost always specified, but normally they are fancy ones. Like I said we argue about it.

The other way to think about it is this, have you ever seen a rain gauge? just a clear pipe with markings showing how much water went into that opening. Not to mention a cap keeps out leaves, dirt/pollen, bird crap, dead bugs, ice, snow, etc. I’ve gutted homes before, it is amazing to see what winds up where.

I’m more of an ounce of prevention is worth a pound of cure type. Many people go without them and don’t seem to have issues. Just one guys .02.


Use a hotter mix and it will come off, it’s organic but it is typically more stubborn than the rest of the mold and mildew.