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High Heat Mortar Primer - Forno Bravo Forum: The Wood-Fired Oven Community

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High Heat Mortar Primer

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  • High Heat Mortar Primer

    Hello all,

    The topic of mortar comes up often, so we are making this a sticky posting that will always be at the top of the "Getting Started" forum for reference.

    Here is some good background information on the high heat mortar you should use to assemble a Forno Bravo Casa or Premio pre-cast oven, or to build a brick Pompeii Oven.

    The best solution is to use Refrax, or another pre-mixed true refractory mortar. We stock Refrax and highly recommend it. It is pre-mixed (just add water), sets hard, is easy to work with, fully cured quickly, and is heat resistent to 1700F. Basically, it's made specifically for pizza ovens and fireplaces.

    If you don't want to worry about shipping Refrax, or want to save some money, you can make a fire clay/Portland cement mortar. Fire clay is a heat resistent clay made up of aluminate and silica. When you mix fire clay with Portland cement, sand and lime, you get a mortar that is more heat resistant than concrete (Portland cement with a sand and gravel aggretate), though less resiliant or thermally conductive than a true aluminate mortar.

    Here in Sonoma county, you can get fire clay from our big, local masonry supply company, SBI -- who is also a Forno Bravo oven dealer.

    Here is the recipe for fire clay mortar, where you measure by volume (use a bucket or shovel to measure):

    1 part portland
    3 parts sand
    1 part lime
    1 part fire clay

    In between Refrax and fire clay/Portland cement mortar, you can make your own aluminate mortar. It is hard to work with, as calcium aluminate can be challenging. If you get the mix, or water wrong, it won't set correctly. It partially sets very quickly, and you cannot re-hydrate it, so you have to mix it and use it in small batches. Still, if you are trying to save money and want/need the heat resilience, heat conductivity and longevity of a true aluminate mortar, it works.

    1 part calcium aluminate
    3 parts sand
    1 part lime
    1 part fire clay

    -James
    __________________
    Pizza Ovens
    Outdoor Fireplaces

  • #2
    I have a question. I have been putting my firebrick up with which i guess is your original fireclay mix of 8 parts sand, 3 parts portland and 2 parts fireclay. But now i am reading about the new mix of 3 sand, 1 portland, 1 fireclay and 1 lime. Am i going to be ok with the other mixture? I am up to my 7th chain. I will change over from this point. please inform.

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    • #3
      The original recipes works great

      Don't worry. The original recipes works exactly the same. The main different is texture in application. The two mixes are very close. Also, 1:3:1:1 is so easy to remember.

      James
      Pizza Ovens
      Outdoor Fireplaces

      Comment


      • #4
        Re: High Heat Mortar Primer

        An update. I have created a High Heat Mortar page within the Pompeii Oven plans, with links to it from the Materials, Oven Dome, Overview, etc. pages. This should point all of the new builders to the same place for the same alternatives and recipes.

        Let me know if you find reference to any older information on other Pompeii pages, and I can fix it.
        James
        Pizza Ovens
        Outdoor Fireplaces

        Comment


        • #5
          Re: High Heat Mortar Primer

          I can't help myself, so here is Nick's buried testimonial for Refrax from an earlier posting. From the source...

          "I've used the 1,3,1,1.. The heatstop 50, and have found (Forno Bravo's) Refrax to dry way harder than both. If I slow cure it with damp burlap it'll take a bunker buster to break it I reckon. "
          -Rebrick (himself)

          You can take that to the bank. Thanks Redbrick.
          James
          Pizza Ovens
          Outdoor Fireplaces

          Comment


          • #6
            Re: High Heat Mortar Primer

            Question about the home brew. According to the book "Bread Builders" by Allan Scott, MASONRY CEMENT is Portland Cement with lime added. So instead of taking portland cement and adding lime, could I use Masonry Cement? If so which type and would it then be 1 part masonry cement, 1 part fireclay and 3 parts sand?

            Thx
            Check out my build at:
            http://www.fornobravo.com/forum/f8/t...uild-4678.html

            Comment


            • #7
              Re: High Heat Mortar Primer

              Hi,

              I am using the attached specification fire mortar for the complete oven. I have no idea what the constitutes are in the "home mix" which is recommended (fire clay, portland cement etc.). Would it be comparable to the shown specification?

              karl
              Attached Files

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              • #8
                Re: High Heat Mortar Primer

                I'm no expert but this looks similiar to Heat Stop 50

                40% alumina
                50% silica
                2% iron oxide


                A little higher in Alumina and a touch lower in Silica but with a rating of 1400 degrees C, my guess would be that it should work fine. Heat Stop 50 is being used by a lot of builders with no problems. Search the forum for alumina and you'll get a bunch of info. There was a discussion about matching the alumina content of the mortar to the alumina content of the brick to match expansions but I don't think a definite conclusion was reached.

                Bruce
                Sharpei Diem.....Seize the wrinkle dog

                Comment


                • #9
                  Re: High Heat Mortar Primer

                  When using calcium aluminate cement I found that adding lime in the mix made the mixture "go off" really quickly. On researching this I found, from the manufacturers (can't remember which one) that they said "do not add lime as it acts as an accellerant, which is exactly what I had found. Do not add lime if you want to keep it workable for a reasonable period (eg 1/2 - 3/4 hr or so) .The calcium aluminate cement is very temp dependant. Use chilled water if using on a hot day and don't leave the stuff in the sun to get hot.
                  Kindled with zeal and fired with passion.

                  Comment


                  • #10
                    Re: High Heat Mortar Primer

                    Question still remains, "instead of taking portland cement and adding lime, could I use Masonry Cement? If so which type and would it then be 1 part masonry cement, 1 part fireclay and 3 parts sand?"

                    Thx
                    Check out my build at:
                    http://www.fornobravo.com/forum/f8/t...uild-4678.html

                    Comment


                    • #11
                      Re: High Heat Mortar Primer

                      Not absolutely sure,but I think the masonary cement is 50% portland and 50% lime anyway. You might need to contact the manufacturer for specs. or just do the mix yourself.
                      Kindled with zeal and fired with passion.

                      Comment


                      • #12
                        Re: High Heat Mortar Primer

                        Went to a local masons yard and turns out I was able to buy Portland Lime. It is a mix of portland cement and lime 1:1.

                        Perfect.
                        Check out my build at:
                        http://www.fornobravo.com/forum/f8/t...uild-4678.html

                        Comment


                        • #13
                          Re: High Heat Mortar Primer

                          Not really sure how I missed this posting and apologize for it...type N masonry cement is mixed at 50/50 portland to lime as is portland lime mix...in this instance it should be 2 parts cement 1 fireclay and 3 sand...that is exactly what I used for our oven build and it dried nice and hard quite quickly...although we haven't fired it yet I am confident in it as a mix...that will also work well for rendering the dome if that is how you plan to finish it as the type N is a bit stickier than other types of mortar...for the render you can add more sand...typically type N gets anywhere from 6 to 9 parts sand when being used to lay brick
                          Best
                          Dutch
                          "Making the simple complicated is commonplace; making the complicated simple, awesomely simple, that's creativity. " Charles Mingus
                          "Build at least two brick ovens...one to make all the mistakes on and the other to be just like you dreamed of!" Dutch

                          Comment


                          • #14
                            Re: High Heat Mortar Primer

                            I, too, had many questions about mortar.
                            Originally I got a high test bucket of dark refractory mortar to try out. It didn't seem to adhere to fire bricks very well, and needed to be fired to set. Furthermore, it dissolved when wet the next day.

                            Then I consulted a potter, actually two of them, who had built many kilns. They BOTH recommended the fire clay, portland sand lime mix.

                            Knowing the portland is just to knit things together and keep the rain from washing away the clay until it gets fired, I decided to put together the 'mix' of different recipes I have seen. I have worked with many different mortars, and the 3:2:1 ( and 1/2) recipe is GREAT --- fine quartz sand, fire clay, portland, and lime.

                            The fluffy adherent mixture is twice the fireclay to portland ratio. The FINE sand is good to keep the small mortar joints ( as possible) and this stuff sticks nicely ( I am up to the 7th chain with no forms.

                            The clay really retains the moisture a long time, so this allows the portland to set up very nicely without getting all the moisture sucked out of the mix.

                            As I understand it, the mortar is really a space filler, and not necessarily an agent of adhesion. It should get hard ( the fireclay) when fired, and the portland, ( as I have read) will begin to lose strength on the cool down phase.

                            I have been cutting all my bricks at an angle so every piece is a wedge. Theoretically it would stand with just spacers in the back, and hopefully the clay will harden and become at least that ( and hopefully more )

                            Just what I have learned so far. Let me know if I am way off base!

                            Lars.
                            This may not be my last wood oven...

                            Comment


                            • #15
                              Re: High Heat Mortar Primer

                              Sounds great - thanks for the tip! In Houston, all we have in the ground is clay - you need TNT to dig a hole around here Just a clarification: When you say fire clay, you mean straight clay say, dug from my backyard? No additives, right?

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