I would recommend reading this:
In a nutshell, 5.2 adds about 100ppm of sodium, and doesn't really buffer the way it claims to.
It is not a substitute for measuring and properly adjusting your mash pH.
Also, chalk doesn't really dissolve well in the mash. You're better off using slaked lime if you need to increase the pH, but I would never increase the pH unless you're positive, through measurement, that the mash pH is actually too low.