Filling up grout joints during floor deli piping Adam 25 Oct 2011 22:00 EDT

We are In the middle of delippig marble floor and after finishing grinding with metals grout in some places is already flush with the tile but in most places little  below. I was planning on filling it up with the grout Mixed with latex but I have concern about new grout Bonding to the old one.  Did anybody had problem with that?
Grout is non sanded and lines are 1/4" wide, 1/16" to 1/8" deep. Grinding deeper will take too Much time and I really don't think it make sense. Any suggestions?

Adam Bartos
BiO Tile & Grout Restoration
773-575-5515 (c)
847-438-0212 (o)