I don't think you have access to the "right chemicals" so wall void injections will be useless unless you know what chemicals to use, and where to use them. Repellants found in Raid, and other brand names will make things worse at times. What bait are you using?? Terro bait is what I would suggest for the easiest to obtain. You must not mess with the ants as they feed, and no chemicals.
Brian