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Base on existing Cement, is this recommended? - Forno Bravo Forum: The Wood-Fired Oven Community

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Base on existing Cement, is this recommended?

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  • Base on existing Cement, is this recommended?

    Hello I am a complete noob to the whole oven experience and eager to learn all I can to build a great piece. My whole concern before I even begin contemplating the design of my build revolves around a comment I read on the instructions for a barrel oven through brickwoodovens. It stated that it is not recommended to build the oven on an existing cement patio or slab due to the amount of weight it will be delivering to the cement. Is this a true statement or was it a general warning to avoid possible legal issuesI ask because I have mostly only pre-laid cement available to start a build and the area that could serve to dig is small and currently used to entertain my 2 year old baby girl and I just don't have the heart to take up space in her area. Also because this patio is in the back part of my home it has a pitch to help with water drainage, Is it possible to build on top of this cement and later compensate for the angle to make a level surface. Please help as I am a complete newbie and while the info on this forum is great many of the terms are yet confusing and a bit overwhelming. Thank you!

  • #2
    Re: Base on existing Cement, is this recommended?

    A typical patio slab is going to be a relatively thin poor of non reinforced concrete, and who knows what type of prep work was done to the soil, i.e. digging down and putting in a layer of compacted gravel.

    Odds are such a slab will crack when the weight of a concrete block base and WFO is built on top of it. You're looking at ~1000#'s, a couple thousand $ in materials and several 100 hours of labor. It would be a pity to have all the effort and money lost because you didn't put in a proper foundation.

    If you're not able or willing to put in a proper foundation, I think you'd be better off looking at one of the pre made portable ovens with a stand.

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    • #3
      Re: Base on existing Cement, is this recommended?

      That is a good question. I think I agree with Paul though. Last thing you want is put a lot of effort and money into building your oven on a foundation that is "not quite strong enough". I estimated my oven to weigh about 8000 lbs. I would definitely think you want your concrete slab to be re-bar reinforced.

      Comment


      • #4
        Re: Base on existing Cement, is this recommended?

        A bigger problem than the slab is the ovens from that company.
        Old World Stone & Garden

        Current WFO build - Dry Stone Base & Gothic Vault

        When we build, let us think that we build for ever.
        John Ruskin

        Comment


        • #5
          Re: Base on existing Cement, is this recommended?

          There 2 things of major importance that you need to be sure of. 1. Is you foundation going to be up to specification for what you put on top of it and 2. Is what you are going to put on top of it up to specification for what you want it to do.

          Foundations are a bit like insulation, more is better and the minimum will barely suffice.

          Barrel ovens are good for what they are good for and dome ovens are good for nearly everything. Just my humble opinion. You will get all of the advice you can handle once you decide exactly what you want to build.
          Cheers ......... Steve

          Build Thread http://www.fornobravo.com/forum/f3/n...erg-19151.html

          Build Pics http://www.facebook.com/media/set/?s...1&l=1626b3f4f4

          Forno Food Pics https://www.facebook.com/media/set/?...1&l=1d5ce2a275

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          • #6
            Re: Base on existing Cement, is this recommended?

            If the sub grade is prepared correctly then 4" is fine.
            Old World Stone & Garden

            Current WFO build - Dry Stone Base & Gothic Vault

            When we build, let us think that we build for ever.
            John Ruskin

            Comment


            • #7
              Re: Base on existing Cement, is this recommended?

              A bigger problem than the slab is the ovens from that company
              I second that.

              Comment


              • #8
                Re: Base on existing Cement, is this recommended?

                Well that does make a lot of sense I guess when it comes down to all the work you are going to go through why not be safe than sorry. And I really don't know the extent of the way the cement was laid so I guess that really sums it up for me. Digging it is for me I guess, I know the baby will appreciate the times we will be having by the wood fired oven. Now to convince the spouse that I will be robbing the baby of some playing space . Nothing
                I cant fix with a little shopping . Thank you to all who posted I really appreciate the advice and I can now start the planning for my brick oven.

                P.s. the mold option seemed a little cheesy and lacked pride if you ask me, which is how I stumbled across this great forum.

                again thanks a lot!

                Comment


                • #9
                  Re: Base on existing Cement, is this recommended?

                  Originally posted by stonecutter View Post
                  If the sub grade is prepared correctly then 4" is fine.
                  There are quite a few factors that make up the strength, or suitability of a slab for it's intended use. I have to respectfully disagree w/Stonecutter w/the 4" thick slab statement. Will 4" work most of the time, if all other factors are good? Yes. But, just having a 4" slab w/a proper base is, in my opinion, not enough. If you are going to invest the time and money into a WFO on a slab/footing, make sure it's designed to do what you are considering. Anyone considering building a WFO w/block base, etc., should do some research before starting. The difference in time and expense between "rolling the dice" and doing it as it should be done, is not alot, for the peace of mind you will get. Remember, everything starts w/a good foundation. Not the place to cut corners. Just an opinion from an experienced concrete person.
                  My Build:
                  http://www.fornobravo.com/forum/f8/s...ina-20363.html

                  Always go the extra mile. It's never crowded.

                  Comment


                  • #10
                    Re: Base on existing Cement, is this recommended?

                    Mario

                    I also second the comment about a Brickwood Oven, I started to build one and then built a Pompeii instead. See my thread here:

                    http://www.fornobravo.com/forum/f8/3...nia-19283.html

                    Neil

                    Comment


                    • #11
                      Re: Base on existing Cement, is this recommended?

                      It depends on the condition of the slab. It's age and subsiqent condition will tell you a lot about the quality of it. Most standard pours are at least 3000psi, which is plenty to support the oven...even without rebar or screen. If the pour was there before he owned the property, and nothing is known about the pour, or it can't be assessed with any confidence, then it would be prudent to cut out a footprint and pour a thicker pad. However....l


                      I've got my current oven on no concrete footing, just 6" of granite dust, that was compacted in lifts. It has had full weight ( all the finishes except the shingles ) for almost a year, the weight of the base for a 1.5 years. I have been watching the vault for any sign of cracks, there are none. The base has not settled at all. The foot print is big on these outdoor ovens, and the weight is well distributed. Mostly all of the builds on here are framed with metal ( a few wooden ones, like mine) and clad with a light weight finish. The slab isn't supporting a sky scraper.


                      There are variables that put limitations on 4" slabs...like the desired finished dimension. But in general even a 4" is more than sufficient to support an oven. The one exception would be if the final finish like full thickness stone Was being used...stuff like stucco or manufactured stone will be significantly lighter. It would be a good idea to cut reliefs all around the footprint to isolate any cracking.

                      To conclude, if there is any shred of doubt, then why not pour a new pad. But if it was me, I'd have to see some settlement and cracking before I worried about a 4" pour. My words aren't here to coax anyone into building something they aren't confident in.
                      Old World Stone & Garden

                      Current WFO build - Dry Stone Base & Gothic Vault

                      When we build, let us think that we build for ever.
                      John Ruskin

                      Comment


                      • #12
                        Re: Base on existing Cement, is this recommended?

                        You live in a warm area, frost heave is not much of a concern. The concern is crushing your existing slab. I would suggest pouring a reinforced 6 inch slab on top of your current slab and take it out a foot or so past the weight bearing walls of your oven, spread the weight out. People float slabs all the time in areas that do not have frost heave, they tamp the earth, put down a few inches of gravel and pour a floating slab that is strong enough to bare the weight of the oven or what ever. A six inch pour with half inch re-bar cross checked on one foot squares will serve your needs. This method is common when installing masonry chimneys in houses that are being retrofitted with a new chimney that is being built on top of an existing basement slab.

                        Comment


                        • #13
                          Re: Base on existing Cement, is this recommended?

                          Originally posted by stormy View Post
                          ......I would suggest pouring a reinforced 6 inch slab on top of your current slab......... A six inch pour with half inch re-bar cross checked on one foot squares will serve your needs. This method is common when installing masonry chimneys in houses that are being retrofitted with a new chimney that is being built on top of an existing basement slab.
                          This is where my mind was going as I read your thread. Even if you build on the existing slab, you can put an extra block wall directly under the center of the dome, that would spread the weight quite a bit.

                          I built an oven stand for a barrel oven, then switched to the pompeii oven. In my view, the barrel oven is more specialized than the dome oven. Was a good decision. No second thoughts. HTH
                          Lee B.
                          DFW area, Texas, USA

                          If you are thinking about building a brick oven, my advice is Here.
                          Our One Meter Pompeii Oven album is here.
                          An album showing our Thermal Breaks is Here.

                          I try to learn from my mistakes, and from yours when you give me a heads up.

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                          • #14
                            Re: Base on existing Cement, is this recommended?

                            Originally posted by stormy View Post
                            You live in a warm area, frost heave is not much of a concern. The concern is crushing your existing slab. I would suggest pouring a reinforced 6 inch slab on top of your current slab and take it out a foot or so past the weight bearing walls of your oven, spread the weight out. People float slabs all the time in areas that do not have frost heave, they tamp the earth, put down a few inches of gravel and pour a floating slab that is strong enough to bare the weight of the oven or what ever. A six inch pour with half inch re-bar cross checked on one foot squares will serve your needs. This method is common when installing masonry chimneys in houses that are being retrofitted with a new chimney that is being built on top of an existing basement slab.
                            This won't help if the 4" slab is iffy. It may be done all the time, but it's not best practice.
                            Old World Stone & Garden

                            Current WFO build - Dry Stone Base & Gothic Vault

                            When we build, let us think that we build for ever.
                            John Ruskin

                            Comment


                            • #15
                              Re: Base on existing Cement, is this recommended?

                              I strongly recommend you don't pour a slab over your existing slab. If someone is unsure of the base/strength of your existing slab, why in the world would someone even consider placing even more weight on it, then building on it?
                              My Build:
                              http://www.fornobravo.com/forum/f8/s...ina-20363.html

                              Always go the extra mile. It's never crowded.

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