Raising the hearth slab

[joeykramer]

hi all, i am wondering what the best option for me is based on your knowledge. in the picture below, you can see that there is quite a bit of distance between my oven floor and the hearth slab where the countertop would sit. i am planning to put concrete countertops on. what i am thinking to do is add 3" of concrete to the existing slab to raise it up and then add 2" of higher strength concrete for the finished countertop with an overhang to hang over the future stone veneer.

my question is do i frame it up 3" and pour concrete, let that set and then frame up again for the counter top? or do i frame up 3" and another frame on top of that to account for the overhang and fill the whole thing w high strength concrete?

from what i researched, i need to roll on a layer of bonding agent so the new concrete sticks to the old. correct?

thanks for your input.

[deejayoh]

I did exactly as you describe - added ~2-3 inches to the existing hearth, tied it with rebar and bonding agent. For my countertop, I built a form and poured it then placed it. Glued it down with some concrete adhesive. It's been fine. It's much easier to get a high quality surface finish if you don't pour in place, in my limited experience.

[joeykramer]

thanks DeeJay- how did go about tying it in with rebar? if i didnt put rebar in the existing slab to tie in to the extension, do you have any recommendations?
thx

[deejayoh]

I drilled in some screws and then tied some 3/8 rebar to those with wire. You could also drill in and epoxy rebar, but that didn't seem worth the effort to me, as there is not really any structural purpose for the concrete. I just wanted to minimize potential for cracking.