I leave you this tutorial that Applesfera has prepared , for all those who want to install Mountain Lion from scratch, that is, format their HD, leave it blank and install the latest feline version of Apple.
Creating the OS X Mountain Lion installation media
If there is no change when Mountain Lion is available in the Mac App Store we can download the installer that will allow us to update our current version, either Snow Leopard or Lion. The truth is that an update should not cause problems but if OS X is already doing strange things to you, it may be a good idea to do a clean installation. What's more The advantage of this method is that we will be able to update the rest of our Macs more quickly.
When OS X Mountain Lion is downloaded and the update process begins, what we will do is close that window and go to the applications folder. There we locate the downloaded file, with the second mouse button we click on the icon and select Show package content.
A Finder window will open where we will see a folder called Content, we open it and then we open SharedSupport. There is the file that we will need to create our installation disk, InstallESD.dmg. We move that file to the desktop, close the Finder windows, and open Disk Utility.
We are going to prepare our boot disk that could be an SD card, a USB memory, a hard disk or even a DVD. The only thing we have to keep in mind are two details, the first is that the minimum capacity must be 8GB; the second is that the partition table used must be GUIDs for Intel-based Macs to detect them as boot disks.
In our case, an SD card, from Disk Utility we select the unit and create a partition with a GUID partition table. Once created we go to the restore tab. There we select InstallESD.dmg as the source and the SD card partition as the destination.
Now we only need to complete the process and that's it. We will already have our unit ready to install OS X Mountain Lion from scratch.
Installing OS X Mountain Lion from scratch
Once our installation disc is created, the next step is obvious, to install the system. For that we go to the Preferences Panel, Boot Disks and we select the installation disk(SD card, USB stick, hard disk or DVD with the Mountain Lion installer). And we hit the reset button. Another option is to reboot directly and hold down the option (ALT) key while starting the computer.
Starting the Mac from the OS X Mountain Lion installer we will see a first screen in which several options will appear. The first one we select is Disk Utility. What we are going to do is erase all the content of the current hard drive of our Mac. We can do it in two ways, selecting the partition and giving delete within the Delete tab or as I prefer to do it, since this eliminates the possible recovery partition de Lion, from the partition tab select create a partition and accept.
Ok, erasing the content of the hard disk now only remains to install the system. We exit Disk Utility and select Reinstall OS X. All that remains is to follow the steps and once finished we will have our operating system fully installed from scratch. A clean installation that will eliminate system problems that we may have dragged into other versions