How to clean exterior polished concrete?

Commercial
1

The job: Three limestone offices that all have polished concrete window ledges.

Challenge: Obviously I don’t want to apply any pressure but not sure what solvent to use. SH is not removing the black streaks.

Thank you for the guidance.

2

Any pics?

3

What % was applied?

4

Started at 3% and went to 8%.

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IMG_7417
IMG_74174032×3024 2.51 MB

An image of the polished concrete strip around the edge of the roof. Same as the window sills.

6

I’ve only ever had luck using medium pressure, but the other guys should comment.

7

Hot mix, medium pressure after. If that didn’t work then the polish could be acting as a barrier.

8

Tried medium pressure. Nothing. Got a little close at first and left waves in the surface. I’m stumped.

9

I’ve got a few office buildings I clean that have that. It often takes several applications and letting it dwell awhile, like 10min between each one. Much more than 7-800psi doesn’t seem to make a lot of difference. Multiple applications seem to work the best. A lot of times I’ll use a pump up with straight SH in it and that works too. Still need to let it dwell.

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10

Straight SH in pump sprayer, repeat and rinse. High SH like @Racer said has been the only way it’s worked for me. Just takes time……