Cracked Marble Fireplace Surround

[bboomer]

Hi everyone.
I'm a newbie to the group.
I had my mason replace a gas fireplace with a real masonry wood burning one.
Opening is 40 by 29 with a 12" by 12" flew.
My problem is this.
Had the marble fabricators install (4) 12 inch wide 3/4" deep Jerusalem Gold around the fireplace opening.

The top piece developed a small crack from top to bottom in the middle. They replaced it with another piece this time with 2 stainless steel
strips embedded lengthwise in the back of the top piece.
It ALSO cracked.
My question? Is the fireplace burning too hot - I measured it at 185 to 190 degrees in the middle top area (with infrared temp. device) OR is the marble
they are using from an inferior source - should this type of marble be able to withstand 190 degree heat over several hours time?
Any and all suggestions will be appreciated.
Thanx,
[email protected]

 

[Sandor]

Is it real marble or an agglomate?

How are they supporting the marble? What is the substrate? Glue, mortar, etc?

 

[elkimmeg]

Another question why should it be 190 degrees that sounds excessively hot Is air space required been covered up?

 

[bboomer]

They applied the marble against the wall/brickwork with (I believe) thinset.

And I am wondering if 190 degrees is normal for the top wall area over the fireplace opening?

Again thanx for any advice/comments, etc.

Brett

 

[bboomer]

The air space seems fine.

I have a 12/12 flue with a proper air chamber.

I will tell you I had to raise the grate by 2.5" (with cut brick at each foot) in order to get good air flow, so as to keep the fire burning properly.

BB