Prosoco does make good products. Find the right one for your substrate. Do a small test area, test the product dilluted with water, and let dry. It's a long process, but you won't know if you've bleached or stained the substrate until after the product has dried for at least 10 days. Increase the concentration per test, or if you have a 'hidden' area, you can test multiple concentrations at once.
Preservation Brief 38, Removing Graffiti from Historic Masonry
https://irma.nps.gov/DataStore/Reference/Profile/2219004------------------------------
Kimberly Sandbulte AIA
New History
Minneapolis MN
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Original Message:
Sent: 08-26-2022 07:02 PM
From: Mark Vinson
Subject: Graffiti Removal