Another Hearth Question
I am going to pour my hearth this sat. When I pour I am going to lay down the Durlock Concrete Backer board which will take up 1/2 inch. (I am not resting my forms on the board but I am leaving it there. I have framed with 2X6 which means my hearth will be about 5 1/2 inches thick. Plus I am going to put down the super isol board. Is tht to thick? should I reframe with 2X4s or would that be to thin?
I have plenty of concrete so the amount is not a concern. Will the thicker slab be to much to heat up?
A thicker slab would be fine and structurally very solid. Because the concrete is under the insulation, it will not get hot, so there are no thermal issues to is being thicker. The Super Isol will stop the heat and keep it in the oven.
The extra 2" in oven height also are not a big deal. Typical cooking floor height is between 38"-44", so you have lots of wiggle room.
Alternate to poured base
I will also be constructing my base this weekend. However, based on the heat transfer of the Super Isol board, I intend to place the Super Isol board directly on the backer board with no concrete base underneath. By base structure is constructed of square steel tubing, welded together, and supposedly engineered to hold in excess of 1300 pounds. Does anyone see any problems?
In flooring, that concrete board is used with multiple layers of thick plywood, overlaid with a layer of concrete based mortar before the tile or marble is put on top. It never just floats between joists. You can't use plywood here because of clearance to combustibles, but maybe some kind of metal base would give you the support you need.
I'm not a structural engineer, but I think you need to think about how heavy your oven is before you commit to this.
You need something under the oven that is rigid, to keep the floor and oven from flexing. The hearth and stand have to hold the oven up (and take the weight); they have to keep heat inside the oven; and they have to provide a rigid and stable platform for the oven floor and dome. I think you should add a simple concerete slab to provide the rigidity function.
How long to dry
Ok My hearth is poured. I used Durarock concrete board and had that sitting on the block stand. I poured about a 5-6" hearth and will put the super isol on top of that. I have been keeping it wet by spraying it done now and them but how long should I let it dry before I start building the oven?
As soon as the hearth slab is solidified, (24 hr) you can proceed with the next stages, the additional masonry on top will keep the surface of the concrete drying out and weakening before it's cured.
There have been instances of failure of incompletely cured concrete, but mostly in fast-tracked apartment building scale projects. You are unlikely to pile enough weight on that slab to compromise it.
Go for it. Your hearth slab will have lots of time and air to cure naturally, while you are building your oven.
Great I thought I had to wait a week! The super Isol will go on today!!!!
In my case, the base structure of tublar steet is designed to fully support 1300 pounds. There are several horizontal support pieces and a center support column. I am not worried about the base or the cement board.
On top I have put 2" of SuperIsol board. I will build the oven floor on that.
I intend to glue the SuperIsol to the cement board with the glue that James sells and set the oven floor on a bed or Refrax motor.
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