Oxidation on vinyl siding?

Hello, i soft washed a house yesterday it had algae and moss on it and so I down streamed it but now the next day I see it has these white spots where the moss used to be.

Is this oxidation? It’s vinyl siding, never had this happen before.

did you rinse?

That’s algae that needs more pressure to come off.


Hmm, well I recently bought a new gun and the m5 twist but it looked like it didnt have alot of pressure like the regular pressure washer gun has.

I sprayed the SH around the siding but it couldnt reach up to the highest point about 3 stories.

Also I think I only let it dwell for about 5 minutes.

Today I did a deck and I let it dwell about 10-15 min and it didn’t have any problems like this.

What do you recommend should I soft wash again with the gun that has more pressure that I have and let it dwell for about 10-15 minutes again, and rinse after?

Yes I rinsed but I think my dwell time of 5 minutes was probably too short and not enough pressure from the gun I was using.

That AC disconnect box though…

That doesn’t look like oxidation, looks like you didn’t get it all cleaned off. If there isn’t oxidation, just put your hw mix on and brush those spots, it should come right off pretty easy. I’ve had some types of vinyl where the nasty areas leave residue like that behind. I find it’s much faster to hit it with a brush, then rinse it off.

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FYI, you don’t need pressure to clean vinyl. My system is only 100 psi and I’ve never had any issues. I let to hw mix do all the work.

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Reminder to everyone that a fire extinguisher on your truck is worth its weight in gold.


Thanks for all the help everyone!

I just finished up here and this is the after pic.

Just wet but I think I got rid of it.

Downstreamed SH again and used some pressure to rinse off!

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How many gpm?

It puts out about 5-5.5gpm.

Nice. I’ve realized a lot lately about psi and gpm.

With your setup you can reach 3 stories?

With the setup I had here which was about 2-3 weeks ago I had a 2.5gpm dewalt pressure washer I forget the psi either 2000 or 3000.

Now I switched to 4gpm 4400 psi dewalt pressure washer and I can reach 2 stories easily and 3 with a different gun.

I bought these both washers about 2 years ago so knowing what I know now I might not have jumped the gun so quick.

You have 12v setup?

I don’t do it the same as anyone on here, so no need for you to worry about my setup when building yours. I don’t want to muddy up this topic with details, so you can read my post from a couple years ago and comment there if you have questions.

I’ve made some minor tweaks here and there, added covers, cleaned up plumbing a bit, but it’s still basically this:

And yes, it will shoot to the top peak and chimneys on tall two story houses. This is what I use 100% of the time on houses, never a pressure washer.

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