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The stump
01-14-2017, 09:30 PM
Hi all,

I have been combing through the old posts as I am getting ready to put a granite slab hearth over top of my existing hearth (picture attached) as we are putting a new gas fireplace in. I just had a couple of questions:

- i was thinking of laying it on top of existing hearth and glueing with a commercial grade adhesive, is this ok?

- the one issue i have is that the existing hearth isn't exactly level, it probably slops a 1/4" left to right, can i shim to get level or do i need to chip at existing hearth? If i can shim, what type of shim should i use?

Thanks for your help


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Houston Remodeler
01-14-2017, 09:36 PM

Welcome to the forum.

1- No, use a thinset material formulated for such applications.

2- Is the floor off by the same amount? The rest of the fireplace? Having just a level hearth would be the oddball level piece?

The stump
01-14-2017, 10:03 PM
Thanks for the quick replay HR!

Thanks, that was a suggestion from a friend but I wasn't sure....on how to get in place.

The floor is more level than the hearth so it wouldn't look to oddball to have a level hearth but take your point, just concerned about the best way to lay it over top of the existing one...

Houston Remodeler
01-14-2017, 10:18 PM
A good quality thinset spread with a 1/2" trowel with 100% coverage spread this way (

The stump
01-15-2017, 10:26 AM
Thanks HR, do I try and get the slab level with the thin set or just let it sits how it wants to on top of the existing hearth?

01-15-2017, 12:31 PM
I think this is a good place to use the "if it looks right it is right" principle.

Parallel to floor would likely give a tapering joint under slab, which may be more noticeable to many eyes. I'd let my eyeballs be the guide and leave the level mostly out of least side to side. Front to back may be served well by the level.

Also worth noting that the bond to existing will only be as strong as weakest link, which might be paint. The goodness is gravity is gonna do most of the work in this case.

Houston Remodeler
01-15-2017, 01:26 PM
It doesn't have to be straight, it just has to look straight.

Recently tiled a fireplace. Floor was crooked, surround was crooked. The Homeowner had no idea. Never considered it until the tiles went on and I slapped a level on the mantle. The floor went one way, the mantle the other.

After much discussion the HO opted to make the tiles follow the top of the firebox (dead level) and the sloping mantle. This took some doing on my part to get it to look decent. HO was happy enough to tip us $200

The stump
01-15-2017, 03:03 PM
Ok thanks guys, i need to have it close to level as gas fireplace will be sitting on part of it, but i think it would be close right now so shouldn't be to big a deal.

Thanks for the video very helpful, given this is going to 1 1/4" granite gravity definitely wont be a problem!

01-15-2017, 05:26 PM
Is this a gas insert with trim panels top and sides? I'd probably check lintel on top of existing fire box versus existing hearth. Knowing how masonry fireplaces at built, I'd bet they are close to one another.

Here's a tell: did you notice things were out or level before you stuck a level on it? If not...well there you go!

FWIW, gas insert fireplaces I've installed didn't care if level or not. Would still be a visual thing.