Everyone knew he was trying to put these weapons together and everyone knew he had no problem using chemical weapons on civilians.

Chemical engineer.

If the concrete does discolor, pressure washing and certain cleaning chemicals will remove most stains.I like Jack Bobeck comment about a 7-day right to cure.

I currently own and manage 3 rental properties that are bringing me about 1000/month for all 3 rentals along with having a full-time job in our local chemical plant.

Do it right by using a scoring tool, then strip the paper (chemically is easiest, depending on your sensitivities) and make sure that you neutralize the stripper according to the directions on the chemical.  

I was able to get them out of a 4 unit property by properly treating all the units which chemicals.

It has has been repaired using "compaction chemical grouting method" which is the normal method of repair for these type problems at least from what I find researching it. 

Next need a list by tenant of any chemicals and how they are discharged by air, water, etc and their containment.  

Its made with similar chemicals as PVC but they claim its more flexible. 

There was one small room (bathroom) I had to wipe down the walls and ceiling with a chemical cleaner before the repaint because it was sticky brown with tar.