Need some help from the Stucco experts

Hello everyone! First and foremost I’d like to thank all the helpful users in the forum from which I’ve learned a ton from and continue to learn everyday. I ran into a very particular situation last week and I’m hoping someone on here can chime in with some of their expertise.

Basically this home has some discoloration/stain on the stucco that doesn’t seem to be organic - I clean A LOT of stucco, and this was my first time running into this particular “stain”. As you can see in the pictures it is only in certain areas - previously they had hired a guy to come pressure wash and he attempted to wash with pressure and you can see the results of that in the oval shape on the front. I had previously advised the client that I wasn’t sure if the stains could be removed and I would have to do tests spots - this is what I did to no avail:

  1. DS hot house mix - basically hitting the wall around 1.5% (I will attach another before/after pic that I did this weekend of stucco with this exact mix and it cleaned up fine)

  2. Pump sprayed a little hotter mix about 5-6%

  3. Tried a little bit of Oxalic

After none of this worked I told the client I would try to inquire about a different solution and get back to her. I’m aware that the only solution may just be to paint and she knows it too. There’s also cracks on some of the stucco (not sure if that matters)

This last picture is the before/after of an eye doctors office we did on Sunday. All stucco and contrary to what some of you on here say, yes it was all down streamed - straight 12.5% SH with a pinch Elemonator using Bobs hi-draw injector, 200 ft hose, and our backup 4/4 to pull the hotter mix and rinsing with main machine - ended up using about 20 gallons of SH total (4 sides and parking lot post treat). The green came off with with the first pass, black stuff had to do 3-4 passes (didn’t rinse, just kept the windows wet and kept hitting every 5 minutes or so)…


I’m surprised you DS’d it since you say you clean a lot of stucco… it all would have came off first hit if you used a stronger mix. Would have saved a lot of time. As for the first pictures it doesn’t look dirty it looks like a poor stucco job. It has most likely looked the same since it was done. I would ask if it’s always looked that way. Out of curiosity, was this mark always there? Looks like it was hit with a surface cleaner lol.


Honestly DSing works for me and stucco. 9/10 times I only hit it once. These were some particularly bad stains but they still cleaned up fine. I know that I can save myself some time and chems if I were to start using a dedicated pump and that’s in the works - hoping to have it all set up by next month.

Yeah I’m thinking it was also a poor stucco job - the builder did 4 of the same houses next to that one and they all have the same issue. Yes lol the mark was there from the previous guy they called to “pressure wash”. I’m fairly certain he tried a SC or a turbo nozzle on it.

How does DS stucco work so well for you and not everyone else…also kinda surprised you don’t have a 12v or booster when you clean that much stucco lol. But yea, explain it to the owner and walk away.

You can down stream stucco if the algae is still translucent. Heavy streaks not a chance.

Pull the proportioner from the injector, throttle down the machine to soap, straight SH in the mix tank.

I wouldn’t do it on buildings of this size or anything of these heights. I showed the fellas from Nebraska the stucco that can and can’t be downstreamed when they came down.

On buildings of these heights and size just buy a Bandit. The job will pay for it and you can put it on the shelf when you’re not using it.


@Racer DS stucco all the time.

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12.5% straight with Bobs injector takes care of it about 85% of the time. The other 10% I turn on the 4/4 for hotter mix. The remaining 5% I turn down the work because I know I can’t efficiently clean it without a dedicated pump.

@squidskc I normally turn down anything I know wont clean up DSing - this particular job took about 5 hours total. Including parking lot and sidewalks. The building itself took 1.5 hours I believe. It was just my main worker doing it.

You can ds stucco if you use a super suds sucker. Are you sure that that is not some type of tinted sealer. Looks like a secondary coating to me

Yeah I definitely think it has something to do with how the builders did the stucco and I told her that. Mainly just wanted to see if anyone here had ran into the same issue.

That looks like an acrylic sand finish on top of hard coat (similar to the texture on Chik Filas-very uniform). It looks like the polymers are beginning to break down and oxidize. If you rub your hand across l aggregate would come off and leave chalk on your hand. Those acrilyc coats last 10-15 years without paint depending on exposure to sun and the elements.

They’re right, that’s a surface cleaner blasting the oxidized materials. Your options are do the rest of that panel the same way, do the wall the same way (both risk doing more damage), or tell the owner to paint before there is no finish coat left and the have to resurface the entire wall. The cracks can be solved if they choose the latter and use an elastomeric for the first coat and the cracks are 1/16 or smaller. That stuff will bridge them.


This type of work is exactly why I switched to the 12v. A stucco surface is much more porous and holds onto things in comparison to something like vinyl siding. You can heat up the mix as you go along. Start low and crank the proportioner up. Another thing to consider is the surfuctant you are using. Try using something that will increase dwell time.

Your not looking at organic material here.

This is a set expectations job with a very general cleaning or walk away.

My opinion is walk away.

It will never be good enough for the owners if they are questioning the staining.