A
That's odd... I can read and write my microSD card just fine with ES File Explorer, no root.Full size SD cards have a read-only switch, microSD cards don't.
Since KitKat, only root or an app that owns a folder can write to it, so if you're trying to use one app to write to another app's folder, it won't work. (That's how Linux works and, since KitKat, the card has been considered part of the Linux file system.)