I am getting ready to install some antique reclaimed heart pine over plywood subfloor on concrete. I have read some posts that recommend running diagonally to the room. The main room is 16 x 35. I am installing the plwood over 15 mil stego vapor barrier using Powers Dek-spikes. I will be vacuuming each hole and sealing each hole with Sonneborn SL1 ( a self leveling caulk) to help reseal vapor barrier where spikes penetrate. I do not have any moisture issues with my slab. The flooring is 9" wide x 3/4" thick x 12 , 14 and 16 foot lengths. I would prefer to just run the plywood square with the rooms but will run diagonally if it is necessary. any advice or help on this project will be aprreciated.

Diagonally is recommended. However, if you must run the ply square, run it so the face grain of the ply is at 90 degrees to the wood flooring and stagger all joints by at least 2'. Allow a 1/8" gap between the panels.