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moist clay - Forno Bravo Forum: The Wood-Fired Oven Community



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moist clay

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  • moist clay

    Does anyone have any knoweledge or experience with moist clay(available at art suplies). Can it be used to level bricks or as brick mortar?
    according to the info on the label ,clay withstands 1200 degrees.
    Thanks in advance!

  • #2
    Re: moist clay

    you would be much better off to use a dry fine sand or fireclay to level and bed in your hearth bricks rather than a wet sticky clay. Even using fine (portland cement consistency) fireclay to level my bricks, it required patience and determination to get them right. Trying to do this with a stiff clay would almost be impossible.
    Whatever you use will add a little to your thermal mass.

    Prevention is better than cure, - do it right the first time!

    The more I learn, the more I realise how little I know

    Neillís Pompeiii #1
    Neillís kitchen underway


    • #3
      Re: moist clay

      Frances built her oven with fireclay based mortar (no portland). It seemed to work out fine. It may not be strong enough to build self supporting arches, but for the mortar for the dome it's a proven method.

      Fireclay has some refractory properties. It's also cheaper than clays used in pottery, particularly prepared wet clays.
      My geodesic oven project: part 1, part 2


      • #4
        Re: moist clay

        Hi Mazussa,
        I've been using clay for kilns, and more recently for ovens, for the last 40 years and you should not dismiss the refractory properties of this abundant material.
        The secret is to not have too much 'plastic' clay in the mix.
        In my workshops we build satisfactory, and perfectly working ovens, from equal parts of plastic clay, sand, and stone dust with perhaps the addition of 5% cement.
        My former university students [ANU] built numerous kilns with such a mix and wood fired stoneware and porcelain ceramics to 1300 degrees centigrade with great success.
        As a binder for bricks there is no trouble at the low temperaturers of, say 700 degrees C, and the mix is successful as a stand alone dome for a wood fired oven.
        You may like to see a short video of building a 'clay' oven on www.au.lifestyle.yahoo.com/better-homes-gardens then click on DIY and go to the 3rd page where you will see a photo of an oven.
        Be aware that there is an enormous difference in clays and something labelled as 'Fireclay' may be satisfactory in bonding bricks together but hopeless when it comes to binding a mix for forming a dome.
        I use, and urge my workshop participants to dig their own, natural clay [see test on the Better Homes and Garden web site pattern sheet] rather than buy prepared bagged clay.
        I'm sure the manufacturers would have a heart attack to see you adding aggregrates that they have taken the trouble to remove, at some expense.
        Natural clay mixes have been used for centuries as oven building material and in my country, Australia, termites nests have been 'reconstituted' to build, perfectly satisfactory, pioneer bread ovens.
        The ants have a mix of clay and aggregrate about perfect for an oven.
        The only consideration in making an adobe, or clay based oven, is that it is not weather proof and needs to be protected from the elements.
        Other than that if the proportions are the same it performs very much like its high tech, equivalent.
        Last edited by james; 10-07-2008, 08:46 AM.


        • #5
          Re: moist clay

          Link above will not work go to my next post to get the corect link
          Last edited by jengineer; 10-08-2008, 03:36 PM.


          • #6
            Re: moist clay

            I had issues getting to it too.
            You need to to surf to it.
            go to yahoo austarlia.... dot com dot au (sorry can't post links)
            then use the menus to get there as below
            scroll down and select "better homes and gardens" from the big green "YAHOO!7 LIFESTYLE:" box

            do a search for "oven". There are two ovens there one is brick others is clay.

            Hope that helps.


            • #7
              Re: moist clay Missing links

              here are the links for those interested...

              Pattern Sheet Pattern Sheet
              As for this design we would recommend that you modify the entrance way to get the vent outside of the dome, bring it forward.

              Pizza oven ala Alan Scott 2004
              Yikes this one is old and I am sure that it has already been posted on either this site or the earlier yahoo version of FB - that dates me.


              • #8
                Re: moist clay

                Oh Good Lord, not this again:

                Lay a bed of decomposed granite (what we would call stone dust) to the level of the top of the blocks. Pack this down well until this is hard. Avoid using sand because it tends to shift and not pack down well. The function of the thick bed is to absorb the heat while the oven is heating up, and returns the heat to the oven once the fire is out... Once the granite has been packed tightly into the well, spread and level a 10-15mm thick layer of brickie's sand over the surface as a level bed for the oven floor...
                Not a TRACE of insulation under the floor. You can forget about pizza with this thing. And isn't Australia an arid country without vast forests to combust? Wood must be scarce and expensive.

                And this mess was on Television, so many will take it as gospel.

                And the flue in the dome? Don't get me started. Don't even bother to download this PDF.
                My geodesic oven project: part 1, part 2


                • #9
                  Re: moist clay

                  Originally posted by dmun View Post
                  Oh Good Lord, not this again:

                  Not a TRACE of insulation under the floor. You can forget about pizza with this thing. And isn't Australia an arid country without vast forests to combust? Wood must be scarce and expensive.

                  And this mess was on Television, so many will take it as gospel.

                  And the flue in the dome? Don't get me started. Don't even bother to download this PDF.
                  You should be used it by now! Hopefully the faithful and determined know better! ( And the people who actually read through the plans and this site.)
                  My thread:
                  My costs:
                  My pics:


                  • #10
                    Re: moist clay

                    Perhaps dmun would be not be so adamant if he could see the quality of the pizzas [and breads and roasts] that the 'mess' produces.
                    t is true there is no insulation immediately under the floor tiles - it is 200mm below a 'heat bank', effectively making the floor 240mm. thick. And that's the intention - to retain adequate heat within the 'floor' for long, sometimes overnight roasts and casseroles.
                    Exit gases are controlled by a metal slide over the chimney which acts as a damper, giving fine heat control.
                    This low tech. oven is one of 2 ovens built during the workshop - the other being a conventional, quality refractory structure of castable or brick.
                    It gives participants the experience of building two ovens at the cost extremities [with the low tech. oven costing next to nothing] and numerous participants have gone on to build their own and are totally satisfied.
                    Oh, and it uses very little timber to heat it up.


                    • #11
                      Re: moist clay

                      The video calls for pavers as a base. Here in the US, pavers ae"granular"
                      or cement like.
                      Question: are the pavers one and the same?


                      • #12
                        Re: moist clay

                        I don't want to get into any arguments.

                        The PDF linked to shows in both text and illustration a row of angle irons, supporting a half inch piece of cement board, with a thick layer of crushed stone, a thin layer of sand, and the floor of the oven. No insulation. If this is wrong, it should be corrected, before new oven builders make mistakes based on incorrect information.

                        It also clearly shows the flue inside the dome of the oven, instead of in the entry. I know that there are some rustic ovens that do this, but this is not a good idea. It prevents proper air flow for heating the oven up, and once the door is in place for retained heat cooking, it leaks all the heat out of the oven. Again, if this is a mistake that the illustrator of this two page document has made, it should be corrected before new builders make mistakes and come here saying that their ovens don't reach temperature, no matter how much wood they burn. This has happened again and again. We tell them that perhaps they can put some insulation below their support slab (which this oven doesn't have, btw) and maybe it will heat up more but really, what they need to do, is to do it over.

                        I'm just concerned about new builders, and their getting information that will work for them.
                        My geodesic oven project: part 1, part 2


                        • #13
                          Re: moist clay

                          A 240 mm "heat bank"??? That is 9.45 inches to the metric challenged. ABSURD!!! I'm sorry, there simply is no justification for using this building technique in todays modern age. Hundreds of our members have proved that a 2"-2 1/2" hearth that has good insulation, is more than capable of doing overnight bakes and casseroles. I can put a roast or chicken in my oven the next day, after making pizzas the night before.....Thats 12-14 hrs later and the temp is still 350-400 F with a non-insulated door.
                          You mention the costs - come on, the cost difference is negligible when you take into account the time and hard work it takes to build an oven. Brickie sand and crushed granite are not free, shop around and you can find perlite/vermiculite or Cal sil type insulation board in the quantity needed for hearth insulation for $50-$75 - Money VERY WELL SPENT.
                          Based on just the folks who have joined this site asking for help with their un-insulated or under insulated hearths and are totally frustrated that they can't get their oven up to temp concerns me enough to address the insulation BEFORE my oven is built. Many frustated members have stated they have burned their oven for 3-5 hrs and still can't match the 500-550 degrees of their indoor gas or electric oven - that takes A LOT of wood. How many people are out there with ovens that they have given up on and have not found this site?
                          This building technique may be the way things were done 50, 100, or 500 yrs ago, but it simply does not make sense TODAY....Personally, I really appreciate authenticity, but not at the cost of performance. I didn't bust my butt for 3 months to produce Dominos/Pizza Hut quality.
                          Cost/expense is not a valid excuse, the costs to insulate the entire oven (dome and hearth) simply are not that high.

                          Sorry for the rant, I will get down from my soap box now. No personal attacks intended, just my 2 cents towards the debate. I, like dmun, simply don't want any new members to get any ideas that have been proven to be outdated or ineffective. We want to grow the WFO culture, not create a disgruntled community with giant masonry paper weights sitting out back.