The grinder is not a safe way to remove a tatoo,but I have a nice sandblaster that will do the trick !!!!!!!!!And some Dupont paint thinner for antiseptic,can't be to carefull !!!!
Hire a sandblaster and buy a hawk. Sandblasting cost will depend on accessibility and surface area.
Masonry is normally cleaned with a 10% muratic acid solution. Check the link for instructions.