I wanted to do a fresh clean install of Mountain Lion on my laptop but in order to do that, I needed to erase the disk. Since I used FileVault on the previous install, I couldn’t erase the disk.
I found this tip on the Interwebs.
You’ll have to enter this command in Terminal:
diskutil CoreStorage list
Then copy the logical CoreStorage volume UIUD:
diskutil CoreStorage delete UUID
Quit Terminal and go back to Disk Utility and partition away and start on your clean install.