Porous block

Spent most of the day trying to remove streaks at the top of this building. This is about as clean as I could get it. Slinging about 8 percent sh. 5 passes over the course of the day. After about 3 passes the stains would not lighten up anymore. Suggestions?

Did you get some pressure on it?

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Unfortunately no. It was all done from the ground. I’m confident pressure would be the key but I didn’t quote the job so when it fell in my lap there was no meat in the quote for a lift. Thought sh would take care of it but guess I was wrong.

Looks like a 32’ ladder would work.

Yeah, that’s porous substrate, definitely need some pressure. Sometimes shooter tip can help but sometimes you need to get closer to the surface with some pressure, especially being that height. Much success….

What’s your process? Are you rinsing each time or piling them on? How much dwell time you giving?

I hit several panels several different ways. At the start of the project. I hit the first panel with around 8 percent sh. Allowed to almost dry and rinsed. Hit again with the same percentage and just let it sit for most of the day while I surface cleaned ( 5 hrs or so). Rinsed again. Not much change at the top. So I sprayed it and let it sit over night. Came back and rinsed again. Slight change.

The second panel got a good pre soak before doing the same process that day. ( about the same result as the first panel).

I moved on to do the entire wall several times. Each time allowing an hour or so of dwell time in between.

At the end of all that the rest of the wall panels looked no different that the first 2 test panels I was playing with.

I guess I knew the answer when I posted this. I’m sure it will come clean with pressure but like I said there was no meat on the check for a lift and moving a ladder along that wall seems like a lot of work lol. I was just hoping maybe one of you had a magic pill for me or something

Tried every tip in the arsenal from the ground. Just not enough

Any chance this could be roof tar runoff?

Interesting question. I was wondering that myself. Not sure how to tell unless I got up on it

If you zoom in on the picture you will see every dark spot coming down the wall is right at the cap joint

Yes because rain overflows at these lower spots.
I don’t think it’s tar.

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Anyone else want to support the tar theory on this project?

And one more thing. When I do get these stains removed would it be worth trying to sell a sealant? Not sure if you can even seal that type of block. Thoughts??

Looks to me like its in need of a degresser to start. There is clearly run off on low spots, most likely from pollution. As far as a sealant you could offer it but to be honest it doesn’t need it. Its a vertical surface with zero traffic. If your in the north you could do the ole freeze thaw talk with them and see if they bite. Only siloxane based, it lasts a lot longer, and will penetrate deeper.

Your looking at alot of testing and headaches though. If your not familiar with sealing and dont have a plan to seal that much sq ft quickly…walk away.