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Foundation questions - Forno Bravo Forum: The Wood-Fired Oven Community

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New Forno Bravo Forum Feature

Forno Bravo Forum Community,

You will notice a new forum at the top of the main page called, "Ask Me Anything". This forum will be used for live one hour "Ask Me Anything" (AMA) sessions hosted by people who are knowledgeable in different areas pertaining to wood fired ovens. How it works:
- Each AMA will have a "sticky" thread where the community can post questions they would like answered during the live session. This will allow everyone to participate even if you can't be online for the live session. These questions will not be answered by the host until the live AMA; if you need an answer quickly, you should post it in the appropriate Forum area for the community to respond.
- Another thread will be posted for the live AMA. Registered users who are logged in during the live session can interact with the host by asking questions and receiving responses.
- The live thread will remain in the AMA forum to view after the session.

To kick off our AMA feature, we have invited author, chef and master bread maker and host of Pizza Quest, Peter Reinhart, to be our first host! Peter will be in the Forum on Monday, February 15th, from 7:00 - 8:00 pm EST. If you are unable to be online during the live session, you can post your questions in the sticky post. Peter will answer those questions during the live session on February 15th. You can view Peter's answers to your questions as well as what happened during the live session in the session thread.

We hope you enjoy this new feature! Please let us know if there is a topic that you'd like to have as an AMA and we'll look for a host!

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Foundation questions

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  • Foundation questions

    I visited a Forno Bravo dealer today, was impressed with the product, and am ready to forge ahead with the project. However, the foundation remains a significant obstacle. Since I am new to most construction (I built a chicken coop- that's it) I don't really even know what to tell a contractor about the job.

    I have selected a site, obtained a permit, and hired a concrete contractor, explained my requirements, however, it appears that he spread a large variety of gravel over the existing area without digging it out, and didn't use a compactor.

    I have since read that digging below the frost line is important in installing a concrete slab.

    Do I start from scratch- remove the gravel, dig down 24 inches (I live in Pennsylvania) and then re-gravel and compact the gravel? Is it important to use pea gravel as mentioned in the Pompeii oven plans?

    Another question is whether the pad can be larger than the oven foundation- I was planning to make mine 9 x 11 so as to have extra room for counter space, but now I'm concerned that the weight differential (under the oven versus under the counter) will make the pad prone to cracking. Should I play it safe and just make the pad the recommended size in the Pompeii plans?

    Also, I have read that there are some concrete additives that make the mixture much less prone to cracking in cold weather. Should I look into that?

    So many questions.

    Thanks for your help.

  • #2
    Re: Foundation questions

    Hi, Like anything, you are going to get different opinions about this. I researched this a lot (live in Ohio), tossed back and forth between having a footer, or going with a floating slab. Most state if you put in a footer, your slab will not move, therefore your pizza oven/foundation will not move, I believe this to be true myself. This is very expensive, digging below frost line, a lot more concrete, ect, but it is piece of mind.

    I dug out around 1' below, and added 6" of compacted gravel, then poured a floating slab on that, 6" re-enforced with lots of rebar. After talking back and forth with Mingy (forum guru) and other folks, I decided to go this route, he bascially stated if it heaves and lowers with frost, typically it is universal on the slab. Regardless, by installing 6" gravel, insuring I have a good drainage pitch, I feel relatively confident that I wont have any issues. I did the work myself, and time/material, just didnt have the energy to dig down 3ft, however if I had the money, and a contractor, what not put it on footers to be sure?

    You want to use a gravel that will take the weight and drain, compacted dravel (skeet) is best IMO.

    Pour your pad as large as you want for extra room, just insure contractor installs expansion joints were needed. It will not make it prone to cracking IMO.

    Not sure about additives, sometimes adding fiberglass strands help, but concrete is going to crack.
    http://www.fornobravo.com/forum/f8/p...s-i-18098.html

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    • #3
      Re: Foundation questions

      "it appears that he spread a large variety of gravel over the existing area without digging it out, and didn't use a compactor."

      This is a big no no and you should stop him. You always have to remove the topsoil down to undisturbed ground. The danger of not compacting is that the slab (see below) might tilt or shift. This would be bad.

      "I have since read that digging below the frost line is important in installing a concrete slab."

      That is absolutely not true unless you are going to tie your oven to an existing structure. I am from Canada and it gets cold here and there are plenty buildings built with just a slab. It is true the building may rise a tad and sink back down but this would only be an issue if it were connected to something which doesn't move up and down. I have a large garage built on a slab and there is no problem. A foundation would be an expensive waste of money.


      "Do I start from scratch- remove the gravel, dig down 24 inches (I live in Pennsylvania) and then re-gravel and compact the gravel? Is it important to use pea gravel as mentioned in the Pompeii oven plans?"

      You have to remove the gravel and dig to below the topsoil. I always install a geotextile before I place the gravel. I don't know about pea gravel - it doesn't compact very well but it drains well. I just use 3/4" crusher run and compact it.

      "Another question is whether the pad can be larger than the oven foundation- I was planning to make mine 9 x 11 so as to have extra room for counter space, but now I'm concerned that the weight differential (under the oven versus under the counter) will make the pad prone to cracking. Should I play it safe and just make the pad the recommended size in the Pompeii plans?"

      Can can make it as big as you want. Concrete always cracks but that won't be a major problem if you add enough rebar and reinforcing mesh (the 6x6 stuff) because the slab will act as a single solid piece. Think of it this way: a proper slab won't fail because the weight of the walls is different from the weight between the walls, at least if the site is well prepared and the slab properly reinforced.

      "Also, I have read that there are some concrete additives that make the mixture much less prone to cracking in cold weather. Should I look into that?"

      Concrete cracks because of the stresses associated with curing and differential weight loads. If you properly reinforce, those cracks will remain tiny, or nearly invisible. I have heard about fibers additive but never used them. I use rebar and steel mesh. There are chemical additives so you can pour in the cold, but its best not to pour when it is too cold.
      There are things like fiberglass,

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