man made live rock questions

I am looking into making my own live rock using aragonite sand and
gravel.

I have visited the GARF website as well as several others but still
need more direction as to how long I should leave the rock to cure in
fresh water etc.
Do I really need to spend money on white vinegar to soak it after the
first 24hours or so of curing?

Also, why doesnt the salt in the marine aquarium environment disolve
the cement used to make these rocks? We all know how salt and cement
are mortal enemies.

If anyone has a proper procedure they use to make their own live rock
please let me know.