Insulated Hearth Question

[jcg31]

Ok, so here is a few real newb questions. I just got my two 90lb bags of portland cement and however many bags of vermiculite weighing next to nothing for my hearth pour this weekend. Having never worked with vermiculite (again why I am sticking to the newb end of the pool here) I was expecting some thing a bit more . . . substantial. It is just hard to believe that 180 lbs of cement mixed with fluff is going to create a 4" x 76" x 76" slab capable of supporting much of anything, particularly a one ton oven and a quarter-ton builder. Does anyone know the compression strength of this mix? How long can you work it ? cure time? Just point me in the right direction.

[asudavew]

I don't know the answers to your specific questions........but many people have built ovens using this plan.

Trust the others who led the way for you.

Good luck.

[jcg31]

So with great apprehension I poured the insulated hearth this past Sunday and as I toted my five-gallon bucket of 5:1 oatmeal-like mixture and dumped it in place I was more convinced than ever that this can't be correct. The pour took about two hours and upon completion it was as mushy and useless as I had suspected when first viewing the dry ingredients.
Five hours later - mushy and useless.
Monday morning - a bit more rigid but easily compressed, still useless.
Tuesday morning - solid as a rock, my faith restored.

Who thinks of this stuff?
Jim

[Gentcpa]

Good to know. I am just about to prepare the form for the hearth, so I am right behind you.

[asudavew]

Mine was very rigid in less than 8 hours.............

[jcg31]

Yeah, I think I used too much water.

[asudavew]

Well at least it hardened up.

Made any progress?

[christo]

sounds like other vermiculte experiences posted here. I thought mine would never solify....