I lost faith in them on 2 different projects.It's been our experience that the products at EacoChem are so well formulated and buffered that the scariness of the actual working chemical is reduced .... alot.
You are going to have to use something pretty extreme....concrete dust that has been wet turns into, well, concrete.
I kno Russ at southside told me he had something like that a while back... supposed to be safer than hydrochloric acid. I've never used it! I dont know how well it works on cars, but its worth a shot.