Walter, not sure what you are attempting to clean off, but looks like a "restoration" type job. You may want to contact Jim Dietrich at Dietrich Technologies. Find link on Delco. Sharp dude.
i would check out www.woodstrip.com and talk to russell he sells a masonary detergent called NM80 its made by a co. called www.eacochem.com
well worth looking at.
hope ive helped.