Here is where it gets interesting... No mesh, it is lath and plaster. I've had to cut into it in a few rooms and if there is a mesh I have yet to see it. I am wondering what was used in the plaster at this point.
https://blog.ibwave.com/a-closer-look-at-attenuation-across-...
I am tempted to disolve a bit of the plaster and run a conductivity test on it for fun. It is like living in a leaky faraday cage.