Do you have any idea how much work it takes to get to the surface of a column. And then getting the wires around?It was so simple......they just drilled a hole in a column. charged it slightly. inserted the nozzle of a spray gun and sprayed the stuff on to whatever thckness they required. Filled it up even.In every column on every floor if they had chosen to.
All without leaving traces or anyone asking questions.

Then comes the bit about what to insert and why.
(I have spent a whole day removing drywall and ceiling plates to get access to the outside of a steel door frame and installing a code lock solenoid)