Tough stains on shingles

Anybody run into anything like these before? We cleaned the roof last week, and some stains seemed to remain. Sent a crew back today, and they’ve been spraying it hot for a few applications. No change at all in the stains.

What % is being spayed?

We did it last week as usual (typ. 3-4% max.), so for a 2nd trip they started at around 4.5%. They said they kept turning it up as it didn’t respond, well over 45 mins at the point the pics were taken. They tried a little agitation, which seemed to improve it a bit (but it was still wet, tough to say for sure). At this point it obviously can’t be organic…we can’t brush the entire roof, it’s 12/12 pitch and 5000sf of it. It will never look even no matter how hard we try.

That’s unusual.

Are you sure of the % and if it’s fresh sh?

Me thinks you have some bad SH. That definitely looks organic. If there is heavy tree cover over the roof it’s likely a mixture of sap and pollen and that stuff takes a HOT mix to get off.

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They filled it out of the holding tank this morning. That was filled a few weeks ago…as fresh as it has been all season.

They didn’t spec how hot they went, but it sounded like they went all the way to “full SH”, which I would say is probably in the 11-11.5 range, with surfactant…we haven’t seen any other issues that I know of from the SH though. That was my first thought too…but by all accounts washes have been going just fine.

I asked about trees right off the bat, these are the closest to “overhanging”…about 20’ by my techs estimation.

Some parts were a little damp from a mist of rain before they got there, but nothing that should impact the work…

The yellow in this pic looks like it did something but wasn’t strong enough to get the full effect. I’d grab a gallon of known fresh SH and test a 1x1 spot right in the middle with 50-50 mix and see what happens. May need to go up but typically 6% is going to show some sign of working. Also, have you verified that the proportioner is working as it should? Can turn the dial to full SH and have a leaky check valve still pulling water in.


Yep, we actually did a lot of maintenance on that truck today. I’m going to make sure we didn’t miss something that was a possible cause.

As for the SH…if it’s bad, then the supplier is going to have to come drain the tank, I got a LOT left in there lol.

Had 2 roofs in my development with same issue, hit with straight sh did budge, moss turned in 30 seconds black streaks did not, was at a loss for explanation to my customer but they were happy moss removal, articles from inspectopedia


For reference:

That’s pretty interesting. I’ve never seen that personally. This streaks look much more uniform than what @JAtkinson posted above. Those seem to start from a small point and gradually expand and stain as it runs down. The ones in the pictures above don’t seem to do that but that could be it.

Get you bleach fresh each week. Don’t sit on it for weeks

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Not everyone has the volume of work to be ordering weekly. If stored properly (out of the sun, kept cool) SH should last several weeks to a month or more with no noticeable degradation. I was using leftover bleach this spring, from the previous fall. Had to pull the proportioning tip and run it straight, but still worked fine for house washing.


I’ve had sections before that I’ve had to hit 5-6 times with strong mix to get rid off. Fortunately not often, but perhaps once/yr.

@JAtkinson what was the dwell time in between coats of full strength? They may need to give it longer to work. I’ve heard sh needs oxygen to work, which I’ve seen where I used to recoat something after a few minutes if it wasn’t dying, and it still wouldn’t die, but then if I left it for longer I would come back and that coating was more effective.

Edit-also, I agree sounds like your bleach is a bit old to get rid of tough stains. I can tell the difference bleach that I received from my supplier that they got yesterday and then when they received it two weeks ago. Also, at least with my supplier, sometimes it comes in hotter than others. I got some about a month ago that came in the day before and they said it tested at 18%. :exploding_head::partying_face: Boy could that stuff clean! Went a long way. :grin:

Way more than sufficient…I think they said like 45 minutes or so when they weren’t seeing results. They just kept turning the dial and waiting longer.

The thing is, there’s nothing new in the delivery/storage system that we haven’t been doing all summer. We had to go away from getting totes because we were spending too much time moving them and trying to pump out of them. We may not be quite at the volume this month as previous, but still the tank was only filled a few weeks ago. It was done every 4-5 weeks during high season, and we never saw any drop off in the cleaning power. All other guys pulling from the same tank said they maybe saw a little longer dwell needed this week, but only after I asked specifically if anyone had noticed that. No one has seen such a massive lack of “cleaning power”. Even if it was weak, it’s virtually impossible that it could have gone entirely inert, so it should have done something. Best guess is it almost looks like something petroleum based, but not a clue how that would wind up up there…plane crashed on his roof???

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Shingles are petroleum based so the seepage issue mentioned above could make sense. Can’t say I’ve ever seen it.

I agree with you on the sh. I think our chemist said it levels off at around 6% and as you said yours probably isn’t even close to that. Maybe try it straight out of a pump sprayer just so you know it won’t clean it.

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