As Hashirama got his instructions on the first technique. He spends time first gathering up Earth chakra on the right side of his body and water chakra on the left side of his body. Being a master of chakra control Hashirama makes sure that the chakra is divided perfectly between the two types of chakra. As he makes sure the chakra is even, Hashirama then begins to finely mix the two chakra within his body. Hashirama takes the time to mix the chakra after making sure is is completely molded into wood chakra he then proceeds to perform the handspans he was instructed to. As he performs the hand signs, Hashirama releases the built up chakra to create pillars around him in which to change his appearance.
Note: hope that was okay don't know exactly how this works