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  • My build in the UK



    Hi,
    Well underway on my first build now and really enjoying it, probably my favourite project I've done at home to date.
    Quick question...
    Can i fill the gaps on the outside with a perlite, lime, cement and sand mix? The mortar is ready mixed and quite expensive and i already have the other bits.
    Thanks

  • #2
    Back mortaring the joints would be better using fireclay instead of perlite in a 3:1:1:1 ratio (sand, clay, lime, cement). Perlite is an insulator and will weaken the mortar mix. I cannot tell, it the dome wall sitting directly on the concrete hearth and not on any insulation? If so, just me aware, that the oven will lose heat as the dome heat will transfer down into the hearth. Also, what insulation is under the floor.? I know there is nothing that can be done you just need to be aware.
    Russell
    Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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    • #3
      Originally posted by stonejumper View Post

      Hi,
      Well underway on my first build now and really enjoying it, probably my favourite project I've done at home to date.
      Quick question...
      Can i fill the gaps on the outside with a perlite, lime, cement and sand mix? The mortar is ready mixed and quite expensive and i already have the other bits.
      Thanks
      You don't say what kind of mortar you have been using, but it is possible you are using an unsuitable mortar designed to sinter at far higher temperatures than your oven will see. If so you may find the mortar unsuitable. Do not fill the gaps on the outside of the dome with a perlite mix as will result in a mix with very low strength as well as having little thermal mass. A brew of 3:1:1:1 (by volume) of sand, portland cement, hydrated lime and powdered clay is a far stronger solution that also provides more thermal mass.
      Kindled with zeal and fired with passion.

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      • #4
        Hi and thanks for the replies.
        There is 50mm ceramic fibre board under the floor and arch but not the outer dome ring as i didnt quite order enough! the cement i've used is an outdoor oven cement made by a company called Vitcas in the UK, by the looks of it they are the main people to get oven supplies here. I have ordered another 20kg of cement but i think i will order a bag of powdered clay its not too expensive, thanks for the advice nearly went ahead and just did it. Glad i posted!

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        • #5
          Originally posted by stonejumper View Post
          Hi and thanks for the replies.
          There is 50mm ceramic fibre board under the floor and arch but not the outer dome ring as i didnt quite order enough! the cement i've used is an outdoor oven cement made by a company called Vitcas in the UK, by the looks of it they are the main people to get oven supplies here. I have ordered another 20kg of cement but i think i will order a bag of powdered clay its not too expensive, thanks for the advice nearly went ahead and just did it. Glad i posted!
          Not having insulation under the dome ring will wick heat from the dome which will transfer to your structural slab causing the slab to heat up as well when firing the oven. You may have to use more fuel as a result to get the oven up to temperature as your heating the slab as well. The structural slab is not designed for high temp use and may crack over time as a result. Your retained heat cooking more than likely will be reduced by a substantial amount or not exist at all.

          Ricky
          Last edited by Chach; 07-25-2020, 09:54 AM.
          My Build Pictures
          https://onedrive.live.com/?authkey=%...18BD00F374765D

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          • #6
            Silly mistake, not sure what i was thinking!? All makes perfect sense now. The top of the second brick on the outer dome is 20mm above the top of the floor brick, just for reference.
            After reading quite a bit this morning concrete varies from not liking 300c to definitely failing at temps 800c.
            My options
            Leave it and risk it although i wouldnt be happy with the heat loss.
            Point the dome up when complete down to bottom two courses and then cut out 50mm of bottom course to fit in more board, would take a while but i think it's definitely do able.
            Any other thoughts?

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            • #7
              What type of cooking do you envision? I doubt you will see 300 C at the concrete hearth but it will draw heat away from the dome. If your cooking style is having a pizza party and then cooking something like roast the next day, then you are probably okay. If you want to do several days worth of cooking or baking lots of breads then you need to step back and evaluate your options.
              Russell
              Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

              Comment


              • #8
                Originally posted by UtahBeehiver View Post
                What type of cooking do you envision? I doubt you will see 300 C at the concrete hearth but it will draw heat away from the dome. If your cooking style is having a pizza party and then cooking something like roast the next day, then you are probably okay. If you want to do several days worth of cooking or baking lots of breads then you need to step back and evaluate your options.
                Hi Russell,

                Checked your Google Docs album, wowzers what a peice of art that build is!
                I plan to do obviously some pizza and yes cook some roasts the next day, maybe some bread. I think I am going to notch the bottom row of bricks at about 45 degrees towards the end of the dome and fill with a perlite fill mix, I’m guessing it might get me 50% of the loss back? I've done far riskier things at work and got away with it. I’ll do 4 bricks at a time and fill underneath as I am going.

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                • #9
                  If you do this, the best ratio is 5 to 1, any leaner does not give you the structural support, any thing less does not give you the insulation values. BTW, very nice joint work on the arch. Click image for larger version

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                  Russell
                  Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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                  • #10
                    Thanks! Little update, just about 8 blocks to go into the top now. I wish i would of made the mortar myself so much easier to use than the ready bought stuff from Vitcas, the bricks held really well.

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                    • #11
                      Part correcting the insulation issue went really well only taking about an hour. Cutting 60mm in and 50mm deep. Really glad i spent a bit of time doing it now.
                      I'm casting a base for my chimney tomorrow, can anyone please reccomend a good mix? I'll be building on top of it with clay bricks.
                      Thanks

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                      • #12
                        Originally posted by stonejumper View Post
                        Part correcting the insulation issue went really well only taking about an hour. Cutting 60mm in and 50mm deep. Really glad i spent a bit of time doing it now.
                        I'm casting a base for my chimney tomorrow, can anyone please reccomend a good mix? I'll be building on top of it with clay bricks.
                        Thanks
                        Good job...you will now not have the what if I did this factor when your done with your project.

                        Ricky
                        My Build Pictures
                        https://onedrive.live.com/?authkey=%...18BD00F374765D

                        Comment


                        • #13
                          Coming on quite nicely now, really chuffed so far.
                          I've started my hearth, its just a sandstone slab cut to fit. By the looks of it I'm going to have a 30mm mortar gap, any ideas as i think its a bit thick myself. Not sure whether to tile or paint underneath the hearth so it may well not be seen really.

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                          • #14
                            Pretty good again today insulated with 50mm of cermic fibre and first coat of perlite render. Ran out of sand now.

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                            • #15
                              Before you place the final nonpcrete render be sure let it dry well and begin the cure process. Also suggest leaving a blockout that extends down to the ceramic blanket at the apex of the dome. You can use what you folks call a breather valve. This allows any water that gets in or is in the dome area vent out. When liquid water converts to steam, the volume increases by a factor of 1500. A vent allow the pressure to release without building up under the dome and cracking the pcrete or final render. Attached is a pic of what we use in the States but you have similar versions in the UK available at any auto parts store Eday UK for relatively cheap. Some builders in the UK doing cast builds found some on I think Ebay UK.
                              Attached Files
                              Russell
                              Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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