Is this Limestone? And if so, will 12.5% SH downstreamed get rid of the mold?

SH yes, Downstreamed, No. Get a pump up sprayer and make a strong mix. Likely will take multiple applications

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What he said. Make sure you get good after pics, that will look good in your marketing. Also upsell that horrible driveway.


Agreed on the DW and hand up a 1/3 mix onto that stone, and make sure to rinse really well. Looks like a nice paying job man! Keep up the good work.

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Thank you for the input! What would you charge for a job like this?

If its just those two spots, 150-250 maybe. But i agree, upsell that driveway!

I see a bit of that in my area. Multiple applications of 3-5% SH from the pump up is the way to go. Keep it wet and let it dwell around 10 minutes between application. Don’t rinse in between. Most of it should rinse right off at the end. Persistence is key. You will be a hero when this comes clean.

Depending on the minerals in the stone you may get some oranges and yellows that show up. I’ve read here you can minimize this with OX but haven’t had to go there yet.

My 2c - Think about what your time is worth (per hour) and then estimate how long the job will take (maybe pad for unexpected difficulty), consider chemical, prep, materials, etc. Can also come up with a /sf charge for larger jobs. I always check that back against how long I think a job will take, " I need to finish in ___ hours/days to make this job $x/hour." (and pay any help you are using)

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Careful you don’t turn it orange, neutralize it for sure and rinse good.

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The more porous the stone the better for rinsing… Dense limestone we sometimes neutralize the detergent but 99% of time, we just rinse heavy between applications…

This job was a few months back but the worst we ever done… probably 30+ years of mold growth… Around 400 linear ft

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Thank you for the replies! I went and picked up some Prosoco Reklaim cleaner/activator and their limestone afterwash as well. I’m doing the job Tuesday, I’ll post some after pics for feedback.

Please do! Also, I tend to over explain… I tell the homeowners “I can’t control the fact that some of my mix is gonna to work it’s way to the driveway and you’ll have a silly looking perfect clean white spot and the rest of the driveway will look like… this. Just letting you know that if you have me do the driveway while I’m here, the cost will be x amount a square foot which brings you to x price, whereas a different washer may charge you the going rate of x per square foot and you’d be paying x. Just food for thought.” Customer, “ Will it make that big of a difference?” You, “ You remember when the driveway was new? That’s ALMOST what it’ll look like. I’ll even hit your curbs and gutters on your property line so people know you chose someone who knows what they’re doing.” Them, “I’ll give you my life savings and my first born.”

Sales is just as important as the skills and knowledge of washing/ chemicals. Don’t be shy. It’s how we fill our schedules and feed our families.

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Love prosoco for stone work.