Just drag the pin off the Phys Mat (from the hit result), search for Surface Type… then drag the pin off the Surface Type node and search for Switch (which will give you a switch by surface).
I hope that’s clear enough 
Just drag the pin off the Phys Mat (from the hit result), search for Surface Type… then drag the pin off the Surface Type node and search for Switch (which will give you a switch by surface).
I hope that’s clear enough