Windows Encryption question

Running Windows 7 Professional SP-1 32-bit.  I have a folder with millions of files, most of which are encrypted with Windows EFS.  The folder, itself, is encrypted, but some of the files within it are not. I would like all the files to be encrypted, but I don't have a way of isolating the ones which still require encryption.  If I select the folder's security properties, and tick "Encrypt", to be applied to all the folder contents, I'd like to know if Windows needs to re-apply encryption to the files which are already encrypted, or only to the unencrypted files.  Changing the attributes of the entire contents would take weeks.