I am installing a tile fireplace surround. I damaged the drywall when removing the previous tile and mantel and planned on putting up cement board - particularly since I am installing a heavier traverite tile. It is a propane fireplace, direct vent so there is very little heat.

I can cut out the existing drywall right on a stud (a double stud to be exact) to give myself a good screwing surface for the new drywall. My question is...if I end up tiling a couple inches past that joint (onto the original wallboard) will I run into any problems with that last row of tiles failing because they are too heavy?

I'd like to tile over the drywall joint to minimize the mudding I have to do, but I am not sure if having an extra row of (4"x4) traverite tiles sitting just on regular drywall is dangerous. That extra row would be sitting on mostly drywall compound feathered out from the joint.

probably won't collapse on that last row. you might get grout cracking, though.

Grout cracking? Why? How can I avoid that?