Concrete mantle

Hello,

I want to make a concrete mantle for my fireplace. Dimensions would be about 6.5' wide, 1 foot deep, and about 2" or 3" high.

I'd make the form myself.

I don't know if this is possible. Maybe it would crack and fall apart. I don't know.

The only concrete I've worked with is Quickrete or regular Sacrete. Is there another type of concrete that would be better than those in this type of application? Something smoother, with less gravel?

If so, what is it called and where might you find it?

I'm open to any suggestions.

Thanks.

Tripper

 

Sure it is do-able. Will you be able to secure a mantle weighing 160+ pounds to the fireplace?

 

Concrete will weigh about 18 lbs per square foot at 1.5 inches thick, so unless I'm doing the math wrong a 3" thick slab of that size would weigh 234 pounds. I've built a lot of countertops, etc. with concrete and please believe me when I say they are a BEAR to move around. Trying to lift a piece that big into position above a fireplace and secure it would take a lot of help, effort, and planning.
As to the concrete, a simple 5000 psi bagged concrete mix works well. The size of the aggregate is typically no larger than pea gravel so that shouldn't be an issue. The smoothness is not a function of the concrete, but of the finishing and forming. If you want it smooth but have no experience in hand trowelling to a smooth finish, then you should cast it upside down in melamine. That way, the top and sides where it contacted the forms will be about as smooth as glass, and only the exposed part (bottom of the mantle) will need to truly be hand-finished. Be sure to vibrate the concrete in the forms to eliminate honeycombing, but be aware that there will still be "bugholes" that will need to be patched after de-molding.
For a 6.5 foot span, you definitely need to use rebar in the piece. A few lengths of #4 bar will work well. Good luck.

Pecos