Marks on vinyl siding after wash

Just starting my business and have been reading through these forums…great resource.

So here is my situation. tons of mold on fairly new white vinyl siding. I used xjet with the 9/1 proportioner in 12.5% SH. the mold was removed but required a 2 coats and in some spots a little bit of pressure. Now i notice the siding has some whiter spots than others and am not sure exactly what this is. Looking for some experienced input.

Thank you - Bill

May have used too much pressure…could have disturbed the oxidation if there was any is my guess?

I had unusual stripping on a house and started to see a pattern to it figured out that that is the same layout has the framing showing through. Yours looks like you did not rinse the Sh real good or left on too long…

What surfactant did you use?

Bill, you got any other pics. How about a before pic also.

I thought it may have just needed rinsing so I washed again with SH and gave a very thorough rinsing and the marks came back. I am thinking this is just oxidation marks as quite a bit of the siding was blocked from the sun for several years. Does that make sense?

Thanks again to all the responses and everyone sharing their knowledge.

In my experience, oxidation isn’t so much a big thing on sides that are that green. Now the sides that are in full sun are typically chalky with oxidation.

Depending on how large that side of the home is, I’d offer to brush it with a soft bristled brush on a pole while a HW mix is dwelling, then rise it all off. That lets you feel goof about leaving good looking results and the customer will know you take pride in your work.

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Is the second pic the “before”? If so, looks like lichen to me. I’m new to this myself but see how this growth could cause inconsistent oxidation and/or “staining”. After a basic house wash i would consider any other efforts to deal with this as a restoration service and price accordingly.

Agreed, lots of green means no sun, therefore I to have never seen bad oxidation on the green side. Put your hw mix on and brush it, then lightly rinse. See if those spots go away or at least blend in

It looks like residual green algae. When it gets that heavy, I try to scrub with a brush while it is dwelling.

Have you let it dry for a couple days then come back and look at it?

Algae is a living thing. When it builds up over years like that, it will pretty much eat into the surface of the vinyl and after cleaning leave those marks where it hadn’t layered as much.

I recently did one just like that with similar marks left over. Also had a massive condo contract, the organics had been on the gutters so long the paint was stripped down to bare metal.

Could it be the sunlight has affected some areas more than others which were covered by algae therefore not exposed to sunlight?

That sounds entirely plausible as well.