A bottom plug and a method of using a bottom plug for forming a mono diameter wellbore casing is provided that includes an expandable packer initially attached below an expansion device. A packer setting mechanism is coupled between the expansion device and the expandable packer for expanding the expandable packer and sealingly setting it in an expanded portion of the wellbore casing. A release mechanism is coupled between the expansion device and the expandable bottom packer for releasing expandable bottom packer from the expansion device. Fluid is pumped into the wellbore casing between the cone and the set expandable bottom packer to facilitate forcing the expansion device into and through an unexpanded portion of the wellbore casing, thereby expanding the casing.