How to stop a solid limestone hearth from splitting

[briany]

The hearth is about 1.5 inches thick, and is made of one lovely limestone slab. I've seen a number of other solid hearths that have split and pushed apart from the heat. I know one solution is to slice'n'dice it up and reset the portions so they can expand and contract independently, but I really don't want to chop up that nice slab if I can possibly figure out a dodge.

I'm installing a large stove in, or rather in front, of the fireplace, and it will sit squarely on top of the slab. The heat radiated downwards will inevitably cause the slab to crack due to the difference in thermal expansion between the centre of the slab and the edges unless I can insulate the slab centre somehow...

Does anyone know of a solid, fireproof, insulating material that could take the weight of a substantial woodstove (120-odd kg)?
Would mounting the stove on a layer of clay bricks or tiles work? A thick sheet of mica-like material, if such a thing existed, might do the trick. Or a layer of those tiles that fall off the space shuttle on a regular basis.
Thanks in advance for any ideas.
Brian

 

[chuckey]

Did this hearth stone not have a coal fire on it? Put down four pads about 3/4" thick to go under the fires legs, concrete/ tiles/ WHY, set'em on mortar to level the tops. Put a sheet of shiny metal over the lot, doesn't have to be thick just self supporting (baco- foil will not do). carefully put back stove, it'll be pretty dificult but I am sure you will manage.
Frank

 

[briany]

Did this hearth stone not have a coal fire on it?
Frank

No, there was an existing stone hearth that I spent ages being careful with not to break as I was removing the concrete subfloor that some genius had put in, only to find out that it, too, was made of dark concrete, so this slab is new.

WHY? Is this an acronym or is my brain frazzled?

B

 

[Schoolmarm]

What Have You.........whatever is lying about in this case

 

[DaveBrigg]

We have a limestone hearth with a solid fuel stove on top, and have had no problems. The slab is about 2 inches thick, and 2ft x 4ft in size. This is the part set inside the fireplace; there is a second, slightly smaller part in front, inset into the floorboards, but this doesn't get hot. We sometimes burn coal, but have never had the stove so hot that it glowed.
Cutting up a slab to prevent cracking seems to defeat the point somehow.

 

[briany]

Exactly! That's heartening to hear that it hasn't cracked, though I was thinking of mounting it directly on the hearth, i.e. no legs, as it will be a bit of a monster to heat 9 rads and hot water. Could get hot under there...

 

[DaveBrigg]

I've not heard of a stove that can be sat directly on the hearth; ours has to have ventilation above, below and on all sides to avoid the risk of overheating. I imagine that if you burn coal, the unventilated stove base could easily reach a temperature of 900 degrees, which is much more likely to cause cracking.

 

[brackendale]

what you need is a nice sheet of asbestos very fire retardent and also comes in 3 colours brown white or blue to match existing decor. Alternatively I could offer a vast quantity of cementaious asbestos in a charming shade of cream and green.

Seriously I have a small wood burner 5kw mounted on a solid limestone hearth, while raised above the hearth by legs the heat radiated has not been sufficient to cause any cracking. The biggest drawback has been a few dirty marks which were easily removed with a "green scourer" however I would highly recomend making sure the limestone is properly sealed, limestone marks easily.

 

[briany]

Asbestos! Perfect suggestion. Armed with this advice I spent the afternoon mucking about with a load of old asbestos sheets that were lying out the back. Took me a while to get it right, but now I'm all set. Seem to have developed an odd burning sensation in the lungs, though.

I hadn't thought about the stove needing ventilation. Maybe I'll get by with the hearth as is and stove mounted after all.
Cheers
B