Stubborn black mold help

I’m softwashing commercial limestone facade and none of my mixes seem to take.
I tried 5 gallons of 3% with 4oz soap
5 gallons of 5%
Then batch mixed 15 gallons of 6% with 20oz soap (northstar cling)

Each application dwelled for 20 minutes. After the second application I attempted to rinse but had to get up close and use pressure to remove it.

I applied a 3rd application with 6% and after 20 minutes still stained. I used warm water too since its 55 degrees tonight.

I went through 11 gallons of bleach with no effect.

First application 3% (just after application/20 minutes later)

20 minutes after 5% application

20 minutes after 6% application with misting done to keep it from drying 14 minutes in.

Clearly its doing better with 6% but im still waiting another 20 minutes while typing this hoping it improves.

I bought 16 gallons of 12.5% bleach with me. Am I basically going to do multiple coats with 6% or am I misapplying it somehow?

I used pressure right of the door for comparison. This is after all the bleach treatments

Patience, young grasshopper. I know you’re unfamiliar with softwashing but the #1 bit of advice I can say is slow down and give the chemicals plenty of time to dwell and do their thing.


If you haven’t read this thread yet, do so.

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I did 4 applications. 3%, 5%, 6% and one more 6%. 20 minutes dwell each time. I left the corner section there unrinsed after the last application. Will see if staying on all day does anything.

The stone itself washes fine. It’s that top “lip” that is stubborn. I ended up having to use pressure to get the stain off. However it takes smalls chunks out and I have to bring a ladder to hit the top. Was hoping the bleach would brighten it.

With the 5 gallons if bleach I had left I made an 8% mix and quickly doused several areas. Letting it dwell while hitting other areas. Did decently on limestone but the lip areas again won’t budge. Seriously if anyone knows how to tackle those please let me know. I just got 5 gallons of Gold Assassin and was wondering if that may work.

The last photo shows what I mean about the lips not cleaning. Hit it twice with 8% and a long dwell time. Ended up just spraying with a 40 degree tip. Have to hit the top from a ladder.

This area I hit 3 times with initially 6% followed by 8%. Use pressure to remove the remaining outline of that stain.

I used 16 gallons of bleach total. Gonna batch mixed a 35 gallon tank of 8% to finish the long stretch along Belk and some of Macys. As well as touch up anything from last night.

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I would’ve just went straight SH and some pressure, hot water would have been great too.

Try One restore

y, the really bad spots I would have used pump up straight. Along that lip too. Then hit with medium pressure. I usually just use my 3-7gpm M5. Those concrete or granite lips can be a pain. sometimes have to hit 2-3 times with straight

When you use straight do you put any soap in? I’ve been using about 4oz per gallon of mix. From what I’ve read though that may be too much.

Most the time no. Normal hw mix use about 3/4 oz of Eliminator per gal. I always keep a pump up with straight SH on hand just to hit stubborn little spots. For example yesterday, had stucco house and the window ledges were terrible. So just walked around and hit them with the pump up before I even unrolled any hose. Do the same on nasty stoops.

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How old is your bleach?

Bought it that day from a pool supply store

Yeah you’re right…I usually hit them tops 3-4 times with straight SH from my electric pump sprayer. They will turn out nice…just takes time reapplying.

That doesn’t mean anything. What is the date code on the bottles? I used to get my bleach from a pool store but found out it was four months old stock from the previous year and was pretty weak.

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You did very well, amigo. Just remember, be patient with the SH. Yes, you could probably have gone with straight SH on that lip but I understand you being hesitant to “light it up” since you’re new to softwashing. Regardless, it looks like you’ve got it handled now and the pictures look great.

Thanks! In the end I did end up lighting up some of it. Had a line of tiles and concrete beyond reach of the wand (should’ve got a boom lift). So I used a ladder and lit it up with straight SH. About 12 gallons to hit all 130 feet or so. The runoff got some stuff cleaned below. Then I mixed a 4.5% mix to hit the lower wall. Didn’t do anything for the lips but got most of the wall cleaned in a pass. Did 3 follow on touchups with 8% mix to kill the stubborn stuff and pressure washed anything that still looked dirty after. Had I got a boomlift I could’ve pressure cleaned the upper stone area but it would’ve been $2000 upcharged. Cost about $600 for the bleach, used 64 gallons for the entire job. (Pool supply shop. Once I get a proper chem tank I’ll buy bulk from somewhere. Batch mixing took forever but killed time while dwelling.)

This was a touch up job. I think if they’re happy with the results they’ll want a complete wash for all the buildings, probably just wanted to use up remaining budget for the year.

Thanks for all the help!


After. Got there around 11pm and finished by 6. I expect to be much faster with a bleach tank, proportioner and hose reel. I was hand rolling 50’ of garden hose every time I moved the truck.


And you may find that if you go back after a week of some good sunny days that it has lightened up more

What type of boom lift were you trying to get? A few of the rental stores local to me have the tow behind “Nifty” brand 35 & 50 ft lifts for a few hundred a day.

And I hope you do find a bulk distributor somewhere for that price. I can get a whole 55 gal dum delivered to my house, with lift gate service, for about $200.

Good job though sticking with it and getting it done! Keep up the positive attitude it’ll do you well.

Sunbelt rental has a 40’ articulating lift for $590 a day. This job was scoped for 3 days. A week rental is cheaper but still $1500 after tax and fees. Also delivery fees to the job site. If this was a full building wash it would be better to have it but it was spot treatment only. Having that charge off the bill makes the bid more competitive. I couldn’t get the top section perfectly clean but it is noticably cleaner and the bottom is great. The whole front of this building is similarly dirty but they didn’t include that in the scope. I think they’re testing the waters and if they like this job they may go full bore and ask us to clean the whole complex. Just my hope anyway.

The tow-behind lift is the way to go, if it’ll reach for you. Pickup/delivery is a killer on those articulating booms.


I don’t think my Tundra could handle 2 trailers. Also this job was an hour drive out one way. To deliver seperately would’ve been a huge pain. The company I subcontract for usually has them delivered for building cleanings though. Here’s one of my first jobs that I collabed with them on.