marble is very soft and brittle. I suspect there was already a crack there during install, or caused by install since it's across the very narrow portion. who installed it? how long ago? have you called them?

a marble/stone restorer could prob make it less noticeable

It can be injected with epoxy, but it can happen again if there wasn’t enough expansion room for the stone. And if it’s too close to the heat without being 0 clearance, the epoxy can discolor. So can the stone. Pull out your insert specs and read the clearances that needed to be maintained.

This is a wood burning fireplace. Marble was installed in August/September. Just got around to using fireplace now 😩

Have you called your installer?

Those put off a lot of heat and require a lot of non combustible space around them, traditionally Tile. Tile in smaller pieces with grout more easily accommodates expanding with heat without negative consequences. We see slabs crack around wood burning fireplaces all the time, because they expand al lot with all of that heat they put out, and someone didn’t leave them enough room to do that. Slab stone is best used with 0 clearance gas inserts.

Hmmm... if I replace stone, which is best for this application? For now, I'm just going to live with the crack. It's not very noticeable

Well... idk what else to do... jeeze. Idk if it's worth the hassle to replace

I'd hit it with a light gray Sharpie to eliminate the white, trickle some thin super glue down it, and scrape the super glue to flush after its dried.

For the pros: I understand why it cracked, but not whether this would count as an installation error. What say you?

I'm not an installer, so I'll ask the pros here: If this was replaced, could installation of a decoupling membrane work to avoid a repeat?

A fabricator’s standard assumption would be that someone asking for a stone slab had already checked all the clearance requirements out before ordering it. A better fabricator would ask for the documents that showed the specs and clearances.

But it’s on the designer for the job to bear the brunt of the job coordination between desired look, and real world do-ability. Those worlds often have a clash. Compromises have to be made.

There are a lot of fireplace types out there. If that were 0 clearance, the type most commonly sold today, the heat transmission to the stone wouldn’t have been enough to cause the issue.

No decoupling could eliminate this. That isn’t the issue. The issue is expansion due to heat and thermal shock. The hot spot expands faster than the surrounding cooler stone. A crack is inevitable under those conditions.

Stoners never think to gently round the raw unexposed edges of stone. Had they done so, it would have eliminated a stress riser which births cracks when uneven heating occurs. A stoner taking a tip from a Corian man? Ain't gonna happen.

In that sense, it could be called fabricator error.

Hmmm... @Joseph Corlett, LLC do you think I should fix it now or wait till warmer weather?

No fabricator is going to do a round edge next to a square fireplace. That wouldn’t have helped with the heat crack either. It would still crack. It wasn’t a non radiused corner. It’s the middle of the stone, right above the hottest part. This is incorrect material choices for the situation. A wood burning fireplace isn’t a gas insert, isn’t an electric.

Curious though, is it the particular marble used, or changes to the way that the marble was installed in recent decades? At least in the 1910s and 20s, and earlier it was fairly common to see marble surrounds right up to the edge of the firebox on wood burning fireplaces, and all of these are not cracked.

i'm betting there was already a stress fracture there. Maybe when they brought it off the truck and were carrying it inside since that top portion is a weak part.

Agee Beth - it really looks like that. I had a similar situation once where the installers pressed a bit to hard on the piece as they were setting it and it cracked in exactly that spot. They said they could fix/hide it and I said sorry but it's going to need to be replaced. I'm certain if I had not been there they would have done an onsite fix and when noticed sometime later they would have said it was fine when they installed.

"Hmmm... @Joseph Corlett, LLC do you think I should fix it now or wait till warmer weather?"

Every time there's a fire or every time someone runs their finger over the crack, it gets a little more contaminated and more difficult to repair inconspicuously. Sooner the better please.

Thank you so much!

Is this surround built from multiple pieces or one piece of stone?

Multiple pieces

It would be good to see a picture of the whole fireplace, rather than just a closeup of the crack....

I've had a very similar situation. Brand new linear gas fireplace with marble surround. Within the first few hours of use (two 30-45-minute sessions to burn off the oil) it cracked in 2 places (top/mantel and bottom corner). We are planning to add a heat shield, add another layer of non-combustible board (to get 1" of board thickness) & replace the marble with 4 pieces instead of 1 to allow for expansion/contraction. Any other recommendations?

A color matched Sharpie and super glue would look a lot better than seamed replacement marble.

I am a fabricator. What is the marble set to? Cement board over wood framing? If new wood was used, the lumber normally has a fairly high moisture content. soon as that fireplace sucks the moisture out of the wood it shrinks and twists. This can crack the marble.