I'm building a corner hearth for my pellet stove. I have 1-1/2" of plywood, 1/2" of micore and I'm getting 1" thick pennsylvania bluestone which has been cut into tile like shapes that I pre-measured. I'm thinking of using concrete to set the stones but I'm unsure of what to grout the cracks with. Would it be possible to grout the cracks with concrete? Should I go with a regular grout? I've planned for 1/4" grout lines. This is my first attempt at a project like this so any crticism/guidance is welcome. So far this thing is built like a sherman tank. the outside border is 3-1/4" tall baseboard that I mitred,stained, and secured to the plywood forming a tray of sorts. I have 1-3/8" to go up above the micore to be level with the baseboard trim. I can get some pics up maybe tomorrow of what's going on.