Concrete for Woodstove Floor

The chimney sweeps came today. They told my wife that the concrete on the bottom of the fire box, inside the stove, is cracked and needs to be replaced. My wife confirms that this is so. Questions:
1. Is this really concrete or just a sand/cement mix?
2. Do I need a special kind or just plain old concrete/cement/ whichever?
3. What's the cure time before I can start a fire on the new floor?
4. Would paving blocks be an alternative? Something like those cement slabs they sell at Home Depot, 1" thick and 12" by 12".
Thanks,
Paul
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I use on a steam boiler Boiler Refractory Cement, its maybe 25$ at a supply house. I would fill the Gaps only unless its real crap. Call Tech support on your unit, they got the real answer
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Use fire bricks... those used for lining chimney fire boxes. If your "slab" needs to be thinner than a regular size brick, saw the fire bricks in half (or whatever size). Fire bricks are mated to one another with a type of mud, for fire boxes... very thin coat of mud, 1/8" or less, so the fire bricks are, essentially, butted against one another.
These days, there may be a special concrete for that application, but I don't know what specific kind.
Sonny
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Just to confirm what two others have said, it is a special fire brick not concrete.
If your stove maker is out of business or can not be reached, fire bricks are sold at most brick yards.
This is not the place to use the wrong material, your life and those you love may be depend on your choices here.
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Colbyt
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fire brick and refractory cement would be my first choice.
You can remove the existing materials and use Rutland Castable Refractory cement. You should be able to find this at a masonry supply house, brick supplier, or a fireplace store.
Here is a knowledgeable article: http://www.finehomebuilding.com/how-to/qa/repairing-a-firebox.aspx
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DanG
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