Concrete Cantilever Hearth

[jpbilderback]

I am designing my concrete hearth structure .. 3.5 inches thick. I will pour the hearth and fill the cinder blocks at the same time.

Tricky part that I need help with .. I want to extend extend "counters" on either side and 2 to 3 feet out .. So a cantilevered design with "floating" counters. The counters wouldnt be the full depth of the oven but say 2 feet deep and they would extend about a 1 to 2 in front of the oven base/as the landing.

To save cost, I would use standard concrete mix for under the oven, in the cinder blocks, but I would use concrete counter mix for anything visible.

Do i use rebar? Do i use ladder wire? Do i need corbels/L brackets? Countertop peeps say don't use rebar because typical counters are 1.5 to 2 inches thick.

Am I crazy? Hope this makes sense.

I searched for cantileveled designs and didnt see any such topic, but if i missed one .. Please send me the link. #staycoronafree

[BeanAnimal]

Your are going to need admix and a lot of steel - ladder wire only holds concrete together when it cracks you need structural steel in your slab. The slab will need to be thick enough to accommodate the rebar - Likely 4-6 inches minimum.

In a nutshell - reduced cost and large overhang distance are going to be mutually exclusive here. You will need to cantilever a structural concrete slab. Wedge shaped slab or ribbed (integral beams) will help. Maybe a local pre-cast company can pour you want you want and pretension it. Any way you look at this, anything more than a modest overhang is going to be limited by complexity and cost.

What happens the first time a friend decides to sit on it while he waits for pizza?

[david s]

My design has both a thin slab and cantilevered. By placing the supporting piers under the heavier parts of the oven it reduces the span between the piers, thus allowing a thinner supporting slab, which in my case is a precast 55mm slab placed on top of the piers. In addition the overhang allow you to stand closer to the oven having space for your feet. Steel rebar in the centre of a 3.5" slab should be sufficient embedment IMO.

[NCMan]

I am designing my concrete hearth structure .. 3.5 inches thick. I will pour the hearth and fill the cinder blocks at the same time.

Tricky part that I need help with .. I want to extend extend "counters" on either side and 2 to 3 feet out .. So a cantilevered design with "floating" counters. The counters wouldnt be the full depth of the oven but say 2 feet deep and they would extend about a 1 to 2 in front of the oven base/as the landing.

To save cost, I would use standard concrete mix for under the oven, in the cinder blocks, but I would use concrete counter mix for anything visible.

Do i use rebar? Do i use ladder wire? Do i need corbels/L brackets? Countertop peeps say don't use rebar because typical counters are 1.5 to 2 inches thick.

Am I crazy? Hope this makes sense.

I searched for cantileveled designs and didnt see any such topic, but if i missed one .. Please send me the link. #staycoronafree

One thing you might consider is not filling in the block w/concrete. It's something I see done quite a bit and it's not needed and really does next to nothing in reality. Just a suggestion.

[david s]

The standard method of building with hollow cement blocks is to fill every second core with concrete and bar as well as filling cores horizontally over windows and doors in the same way. The resulting strength improvements are derived by this method.

[Alomran]

Any cantilevered hearth must be reinforced with steel. The rule of thumb for steel reinforcement for the cantilevered hearth must be as such that if you want to cantilever the hearth by 500mm, the steel reinforcement must be double the length of the projected out distance, 1/2 of which must be tied to the main heart and the other 1/2 is cantilevered out. so if the cantilevered hearth is 500mm the steel reinforcement should be 1000mm. Furthermore, it is vital that the steel reinforcement must be either tied extremely well to the reinforcement of the rest of the heart by metal wire or welded. Some make the mistake of hooking up the cantilevered steel reinforcement in a casual way. Reality the steel reinforcement should be tied to the rest of the hearth reinforcement in such a way that you should be able to stand on it and it wouldn't move. I used double mesh for my cantilevered hearth