Tile grout crack with newly installed tile over backer board.

[Catherine Ann]

I recently contracted with a home repair company to install a tile floor.  He came highly recommended by a friend.  The installer suggested using two layers of 1/4" backer board instead of one 1/2".  Now the grout is cracking between the tiles in the heavily traffic areas.  All tiles were installed two months ago.  The Installer says he'll fix by removing the grout and screwing additional screws  through the open grout spaces to tighten the backer board slabs to the plywood underlayment then regrout. Does this sound like a fairy tale fix? 

[Steve Johnson]

It might work...Thats a hard one because it could be so many things...the grout line is just the path of least resistance.  There could be a hump/dip in the floor that is causing a void which is allowing movement....the board may be installed parallel with floor joists which could allow movement.  The joints may just be too large for the grout used, which would cause cracking.   Got any pics?