hearth / bachk hearth expansion joint

[mikedamico]

HI,

I am currently replacing the insert and hearth on my fireplace.

I have been following guides found on the internet and they all point to the fact there should be an expansion joint between the granite hearth and the back hearth.

Can anybody advise how thick the expansion joint should be and what material to use?

Also, can anybody tell me what I should use to fix the hearth to the concrete floor? Is normal concrete ok, or should I use some sort of adhesive?

Thanks,

Mike