well gaara doesn't turn himself into sand at all.....ever. Since this isn't an anime forum this is going to be rampant with spoilers so here goes. He manipulates the sand with the help of the shikaku (one tailed demon) that is sealed inside of him. What looks like him turning into sand is the sand forming a whirlwind around him. The only thing that may look like him turning into sand would be the sand clones which once again, are not for attack.