[Palmetto Home and Deck]

Originally Posted by Paul Kassander

This is a product used to clean concrete trucks that is supposed to work on some thicker build up. Kleen Krete: Construction: Progressive Solutions Corporation

Paul beat me to it, but this might work. I use to use it to clean concrete buckets of dried concrete build up back when I was in bridge construction.
Call your local concrete company to see what they have. Most concrete companies sell supplies such as this to contractors as well as having it for their own use.

What you are up against right now is well beyond this, but one trick I used when ever we accidentally got concrete spatters on some of our equipment and didn't discover it until after it had dried was to spray some WD-40 on it and let soak a while. It doesn't dissolve the concrete, but it seams to penetrate it enough to loosen the bond between it and what ever it was own so you can scrape it off easily with a plastic putty knife without harming the paint or glass. I use it now on new home clean up when I find concrete spatters on windows and vinyl siding etc.