In article ,
"Vinny P." wrote:

I mounted an 802.11 WiFi antenna and was dismayed to find two drill bits
dulled (I don't think I've dulled more than that in my entire life) just
trying to drill an inch through stucco to mount an antenna.

There is 'something' as hard as a steel beam one inch under the stucco
near the roofline that just can't be drilled through.

What could possibly be there (in the wall?)?

The reason I ask is I have to replace the flimsy mounting arm with a
stronger one from a Dish TV installation - so I'm going to have the
problem again.

I'll choose a new location - but I don't have much choice within a few
feet given I need line of sight to the WISP access point.

What could it be that is hard as steel one inch below the stucco?

I'll let others speculate on what you're hitting, but steel can be
readily drilled.