concrete fireplace mantel

Hi,
I am forming a concrete mantel above an existing fireplace. I will then cement on Sandstone to the concrete mantel as the finished product.
Before I concrete it, I wanted to know whether there is an addidtive that would make the concrete more heat resistant and less likely to crack. Any advice on the concrete mix would be appreciated !
thanks - Anth
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Don't worry about the heat resistance on a fireplace mantel. The amount of heat is small. There are additives for less water and quick curing not necessary for heat if I remember correctly. Use 28 day concrete strength of 3000 psi for the mantel it should be strong enough. Not less than 1 1/2" thick. You should have a good way to support the concrete mantel prior to the installing the sandstone. The concrete mantel will weigh about 18 psf.
CID...
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