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My first WFO build thread... I'm torn clay/cob or the much discussed homebrew cast

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  • My first WFO build thread... I'm torn clay/cob or the much discussed homebrew cast

    Hello all from the UK and 'sunny Lancashire'

    Just spent the last hour and a half reading threads by mullster, aaronpizza and a few others. Im now torn between what i wanted to build, and now what i think i can build.

    i don't have a huge amount of space to start off with so i think im limited on internal diameter size (and ultimate completed size). The patio in the photos is about 3m x 2.5m, the wall at the back is third party so also want a gap there that I'll eventually put trellis in. The bricks i got free last weekend from a neighbor.

    This isn't likely my forever home so isn't likely my forever oven so a bit reluctant to spend 's and 's.

    What are people's thoughts on a round v square base? I prefer the round i think but would be awkward to get plinth / lintel cast. I also envisage the base being hollow as a wood store and build a little side/ worktop area out of sleepers.

    So... I'm going ti build directly onto the patio flags, they're 2x2's at 50mm and have been down for years, not moved at all with heavy use.

    if i build clay, i reckon i can get away with a 75cm max internal diameter, 10cm clay thermal mass layer, 10cm cob/ straw insulation and then some form of third clay layer with a lime cement waterproof render and decorative finish. Does this seem reasonable? Can it be built on a sleeper made lintel platform or should i stick to concrete?

    After reading the other threads on the home brew casts, i really am torn.

    Im going tik keep this thread going as i design and build over the next month, so any advice is really appreciated.

    Thank you. And keep up the good work on the other threads.

  • #2
    Hi Robarb.

    I'm new to oven building myself and currently in the process of building a smaller 21" internal oven.
    A 75cm internal oven is a decent sized oven.

    I really like the round base and did consider it myself but I went with a block work U shape in the end as it was easier and cheaper. You will lose storage space for wood/tools going with a round base.
    I too have built directly onto flag stones, I don't think its recommended, a purpose made concrete slab is the correct way to go but like you, my flag stones are cemented down and as my oven is smaller I've taken a chance. Don't underestimate how heavy these ovens are once complete.

    I don't know much about clay builds, most of the research I have done is either on brick or cast ovens. Whats your reasoning to go with clay? have you found a supplier for it and whats the cost?

    I'm building a kind of hybrid oven using brick and cast home brew, not for any particular reason other than I thought it might be a little easier to build and I wanted to try both methods.

    Do some more reading on home brew and castable refractory cement. Also research casting an oven over a sand mould, I think for a beginner its by far the easiest way to make a good oven.

    I believe clay ovens are similar, that you mould clay over a sand mould but I'm not sure if you can render over them to finish? the ones I've seen have been makeshift and not intended for years of use.

    Fire bricks pose more of a challenge, there is a lot of work just cutting them as well as laying and mortaring the joints.

    Good luck with the build, keep us posted and ask any questions here, there are a few regular posters with a wealth of knowledge on builds.

    Spend some time reading other threads to as a lot of questions are answered in them.

    Comment


    • #3
      Thanks Hattori-Hanzo,

      I agree, i do like the circle base but i'm not sure if i can pull it off without in-filling the centre (to make it sturdy enough) and losing the wood storage in the process. I'm going to risk direct build on the flags though, we're likely not staying here so it's only going to need to last <10 years.

      I have a few ideas for the base and wondered if they were practical. I've got a few 3x2 and 2x2 flags hanging about, still in good condition and barely used. I wondered if i could double stack these over pre-stressed concrete lintels as a base (see image idea). I like the arch at the front for the wood store, will compliment the eventual oven arch.

      Would this base be strong enough rather than a concrete cast? How thick would the v/crete insulation layer need to be and as per DavidS' recommendations in other threads, will it need some form of drainage hole through the flags to allow the v/crete to dry?

      I think 1500mm x 1200mm (5'x4)' is slightly too large for my space but feel i need at least 1200mm for an internal dome size of 75cm minimum.

      Thoughts?

      I want to work backwards from a finished idea in my head so i only need to order what i need, material wise.

      Thanks
      Last edited by Robarb; 06-07-2020, 06:13 AM.

      Comment


      • #4
        I originally thought clay as i reckoned it would be easier to build than a brick oven. Clay ovens are quite 'thick' though by the time you've added minimum 100mm thermal mass, 100mm cob insulation, and some form of third waterproofing/protective render layer. Plus i think it would be cheaper (i don't want to blow a huge budget on this project)

        Edit:
        I've also just found some 450x450x70mm flags, i could arrange these in a 3x3 arrangement to get a 1350x1350base. Plenty big enough. Would it be thick enough though?
        Attached Files
        Last edited by Robarb; 06-07-2020, 06:33 AM.

        Comment


        • #5
          I'm not the best person to ask about base construction but from what I've researched the recommended way is to build a brick or block base (two sides and a back, possibly a central division too) then use a wooden form to pour a concrete top reinforced with rebar.

          While your flag stone idea seems plausible to me I've no idea if it would be acceptable.

          For the vermiculite insulation base layer you're looking at a minimum thickness of 100mm with a mix ration of 5 parts vermiculite to 1 part cement by volume.
          A lot of people myself included have used an additional layer of calcium silicate board on top of the vermiculite layer. 2" calsi board is roughly equivalent to 4" Vcrete mix
          I've done 3" of Vcrete with a 1" calsi board on top.

          If you're on a budget it's not essential but calsi is a slightly better insulator than Vcrete. as long as you have at least 4" of insulation you should be good.

          A water drainage hole is definitely recommended to aid drying and allow excess moisture to escape.

          I would definitely look into castable dome ovens using home brew if you want to save money and have an easier build.
          Last edited by Hattori-Hanzo; 06-07-2020, 12:11 PM.

          Comment


          • #6
            I agree. I decided this afternoon that castable homebrew is the way forwards for the space i've got, the current free resources i've got or can get, and essentially, what seems like an easy (ish) build.

            I think i've also decided on my base too but i'll see if there's any further input on the flag idea.

            It'll be a 75cm internal dome with a 60mm (2.2") homebrew first layer, a 50mm (2") thick ceramic fire blanket (a necessary expense) and a lime render finish (i think i want to paint or tile it eventually). How thick does the last layer need to be?

            I found the dome/material calculator on here in another thread and yes although it's indicative, it's a valuable resource. That thread should be a sticky!

            I'm just currently working out the amount of firebricks i need (another necessary expense) and how the entrance,flue area works. Can anyone point me in the direction of a similar thread on castables and there entrances?

            What i've got so far...I agree. I decided this afternoon that castable homebrew is the way forwards for the space i've got, the current free resources i've got or can get, and essentially, what seems like an easy (ish) build.

            I think i've also decided on my base too but i'll see if there's any further input on the flag idea.

            It'll be a 75cm internal dome with a 60mm (2.2") homebrew first layer, a 50mm (2") thick ceramic fire blanket (a necessary expense) and a lime render finish (i think i want to paint or tile it eventually). How thick does the last layer need to be?

            I found the dome/material calculator on here in another thread and yes although it's indicative, it's a valuable resource. That thread should be a sticky!

            I'm just currently working out the amount of firebricks i need (another necessary expense) and how the entrance,flue area works. Can anyone point me in the direction of a similar thread on castables and there entrances?

            What i've got so far...
            Click image for larger version

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            Comment


            • #7
              So when people say 3:1:1:1 is that Sand:Cement:Lime:Clay by volume or by weight? What if the clay is in powdered form?

              And cement... Portland... but there's so many different varieties available here in the UK, which is the right one haha!?

              Thank you.

              Lastly, should i be using stainless steel needles AND polypropelene fibres in the homebrew mix?

              Cheers

              P.s sorry for the questions, but do the SS needles also go in the outside render layer?
              Last edited by Robarb; 06-08-2020, 10:12 AM.

              Comment


              • #8
                https://community.fornobravo.com/for...ize#post423276

                powdered clay

                what type is available - can't comment

                yes - refer to David S posts

                no
                Russell
                Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

                Comment


                • #9
                  The 3:1:1:1 is 3 parts sand, 1 part hydrated lime, 1 part powdered clay, 1 part portland cement.

                  The clay must be in powdered form and fire clay is most recommended but it's proving hard to get hold of in the UK at the moment. Any powdered clay should work (avoid ones with added grog) but if you cant find fire clay then ball clay (HV clay) also works and should be readily available.

                  The sand should be fine builders sand not sharp or course sand.

                  Blue circle hydrated lime is cheapest at B&Q at the moment if they have any in stock

                  The cement should be just the regular blue circle general purpose, no need for any of the quick drying or mastercrete stuff.

                  The mixing ratio is by volume only.

                  Ideally you want to use stainless needles in the home brew if casting a full oven, though they are tricky to find in smaller quantities.
                  There was a recent thread where someone found a source for them but I cant remember which thread.
                  The needles add much needed strength to the cast.

                  polypropylene fibres are also a must use. they are not for any additional strength but act as burn out fibres when curing the oven.
                  As they burn away they leave behind tiny voids which helps moisture escape from the cast which should help[ to reduce cracking and stress.

                  The SS needles are not needed in the external render layers.

                  Hope that helps.

                  Edit
                  Utah beat me to it

                  If you haven't done so, search david s posts. Every thing I've written is taken from his knowledge on the subject.
                  Last edited by Hattori-Hanzo; 06-08-2020, 11:12 AM.

                  Comment


                  • #10
                    Hattori-Hanzo

                    Try this website. https://www.valentineclays.co.uk/ It's where i've sourced mine from if you're UK based (or for anyone else that is struggling for that matter). I was quoted 39.00 for 100kg and a further 50 for delivery, but my brother in law lives in stoke near to all the potteries so i'll go get him to collect it I also don;t need 100kg anymore now i'm going castable.

                    The needles, a company do them in South Wales, pembrokeshire way, can't remember the name i'll see if i can find them again.

                    UtahBeehiver Thanks for the forum link an other info.

                    Comment


                    • #11
                      Is it possible to cast a flue/chimney and gallery entrance in one piece? Or would it be too heavy? Would it be possible to cast the dome, the entrance and the flue pipe in 3 different pieces? Just wondering if there are alternatives to flue pipes.

                      Thanks

                      Comment


                      • #12
                        Hi Robard & Hattori,

                        I have found this cheap UK fireclay supplier https://www.castreekilns.co.uk/ They are selling


                        one Fireclay - 25KG - 25KG Bag
                        10.00

                        Fireclay - 25KG - 10 X 25KG Bag= 250Kg
                        80.00

                        Fireclay - 25KG - 40 x 25KG Bag= 1 Ton
                        180.00


                        Cost of ''Standard Delivery'' Zone
                        UPTO 25KG 50KG 75KG 100KG 125KG 250KG 500KG 1250KG
                        8 15 22 29 36 40 45 50
                        and it's worth comparing their prices to other suppliers you have reached out to.

                        There is also another cheap supplier for brand new firebricks https://www.kilnlinings.co.uk/specials, their fireclay is more expensive than the first supplier, but shop around and have a look!

                        I know of a guy in Essex selling the double size firebricks blocks that have been sitting in his barn for years for a good price (I think 3 for a double size brick and he may have about 150-200 bricks). If you are willing to travel to collect from Essex and willing to cut them to your required sizes, let me know!

                        I do have few bits and pieces left from my ongoing hideously, out of control, over-budgeted, 6 years ongoing, gigantic oven project, perhaps the largest ever pizza oven in the entire UK's history and may be it will be the least used oven in the history of mankind!I had in my mind using it for a good cause to cook for the homeless in London.

                        If you can get to Weybridge in Surrey, I am happy to donate Pumice, Vitcas fireplace render buckets, few firebricks (approx 20-24) as well as a sack of fire cement and perhaps a sack of fire clay. Let ,me know.

                        If you need to have a chat on the telephone, you can message me and I can give my mobile no.

                        Keep up the good spirit and build as big as you can, don't cut corners as you will end up paying twice as much!

                        Cheers.
                        Mustafa
                        Last edited by Alomran; 08-10-2020, 03:04 PM.

                        Comment


                        • #13
                          Thanks for the encouraging words Mustafa, it's good to know there are other people out there that also like to think things through 'thoroughly'

                          Once of my work colleagues lives near kilnlinings so I'll be ordering through them and saving quite a bit on postage (we'll share a pizza or 3 when lockdown is over for him picking them up for me).

                          Thanks for your offer though, that is very kind. Ive got a 'plan' now, just a last few things to iron out and then wait got stuff to arrive.

                          Once question tip the pizza oven massive...

                          Could you use a terracotta chimney pot instead of a twin walled flue? I may have a friend who's getting rid of one

                          Comment


                          • #14
                            Originally posted by Robarb View Post
                            Could you use a terracotta chimney pot instead of a twin walled flue? I may have a friend who's getting rid of one
                            Oh that's very kind of you, It will save me the headache of a search. I would love to have the terracotta chimney. Many thanks

                            Comment


                            • #15
                              Just be careful, a clay chimney pot is designed to sit at the top of a chimney, not at the bottom. Because it will see much higher temperatures closer to the fire it will crack unless you insulate around it.
                              Kindled with zeal and fired with passion.

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