On the helipad, it appears Granite or Marble or not really the best. That is a sort of guess from me really, because the FCC website is too much for me at the moment.
AC 150/5335-5D - Standardized Method of Reporting Airport Pavement Strength - PCR (faa.gov)
'This AC provides guidance for using the standardized International Civil Aviation Organization (ICAO) method, called the Aircraft Classification Rating – Pavement Classification Rating (ACR-PCR) method, to report airport runway, taxiway, and apron pavement strength. Includes instructions for using the FAARFIELD program to calculate ACR and PCR values."
It has to be tested and approved for strength.
This applies to helipads too, and I don't really want to go to the ICAO site. But basically, down draft and foreign debris.
Now, with Trump being such a grass expert, I am surprised he did not go with this approved system.
PERFO grass reinforcement for Helipads
Oh, it's Canadian.
But that's the thing isn't it. I am no expert, but the actual experts are just drowned out by the sheer volume of crap he spouts.