The Garage Journal to the rescue! From a post there, here is a product that is supposed to accomplish this, I haven't tried this yet but there is a good chance I will! I would try this on a scrap piece first to insure that this does work without "side effects", it is meant for masonary products.
https://www.amazon.com/gp/product/B001A ... pldnSite=1 [sulfamic acid cleaner] currently listed as "Unavailable"
The Thread over at GJ: https://www.garagejournal.com/forum/sho ... &page=2048 Post #40953 and: https://redirect.viglink.com/?format=go ... %3Bt%3D11s
If anybody has used this please share your results. Thanx Harry