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Mortar? - Forno Bravo Forum: The Wood-Fired Oven Community


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  • Mortar?

    I am going to begin building my oven this spring. I understand the need for fire bricks, but is there anything specific I need to know about the mortar? I would also appreciate any advice on materials to use on the bottom surface of the oven. Can I use a large slab of slate or sandstone?
    I live in the N'east US with extreme temp shifts.
    Thanks in advance for any advice you can lend.

  • #2
    make sure your foundation is above the water line and or provide adequate drainage see




    The floor is not mortared in place. It needs to float due to thermal expansion and also you may need to replace one or 2 firebricks (on the floor) due to cracking (too much wtaer when you wet mop the ashes out). The mortar on the dome is very thin 1/8 inch on the inside or less. since the bricks are rectangular and you are making a circle there will be a signigicant amount of more mortar on the outside.

    Not sure what the concensus is on the using other materials for the floor, The plan has you using the same bricks for the flor as you use for the dome. You need the heat capacity to proper maintain temperature. I don't know the thermal/conductive properites of slate

    Sandstone has been discussed and essentailly ruled out

    hope that helps

    If you can spend some time readiong through some of the posts. Also do and Advanced Search on the keywords.

    je - spell check - nver heard of it


    • #3
      Refractory mortar and cooking floor

      Does anyone have experience, or expertise, with soapstone and other natural stones? I have heard that soapstone gets too hot for cooking, and I don't know how well it would perform at holding heat. Also, I don't think it is porous enough to work well with dough to create steam and a nice crust. That said, I have never personally worked with it. It would be good to hear from anyone who has.

      I find that firebricks are a good option for the cooking floor -- particularly if you get the hearth and oven design right.

      Also, you can buy a 43" floor in four pie-shaped pieces from Forno Bravo. It is the same floor as our precast Casa and Premio ovens.

      For the mortar, I think there are three options, and you choice depends on how you will use the oven, cost and how hard you want to shop.

      The cheapest option is to make your own mortar using Portland cement.

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

      The portland will give out over time, but the lime and fire clay will hold it together. This is fine for residential ovens that won't get a lot of use. Still, as it will break down, you would want to fit your joints as tight as possible to keep the heat away from the mortar.

      The next option is calcium aluminate mortar.

      1 part calcium aluminate (Lumnite is one brand name)
      3 part sand
      1 part fire clay
      1 part lime

      The is real refractory mortar and is heat resistant. It will also do a better job of absorbing heat and will last forever. The downside is the cost and hassle of finding calcium aluminate. It is also harder to work with. It dries fast, gets hot when it is drying, and you can't re-hydrate it after it starts hardening, or it won't set right. You have to work with small batches.

      The best mortar is Refrax from Forno Bravo. It's great stuff. It's made specifically for pizza ovens, firebricks and fireplaces -- there is a graphic of a pizza oven on the bag. It's great to work with, and it sets fast and hard. It's the Kleenex of refractory mortar in Italy. You say give me a bag of Refrax for everything. The only downside is that it costs more than making your own Portland-based mortar, and you have to pay shipping costs from NorCal.

      Hope this all helps.
      Pizza Ovens
      Outdoor Fireplaces


      • #4

        You can also buy LaFarge Fondue refractory cement, already mixed up, except for sand, but it has the same properties of an aluminate you'd mix yourself as James pointed out. However, I live in Ontario, and probably have the same sort of climate, and I used Fondue for my bread oven. It better last forever, it's a hassle to use, and it's pricey.

        "Made are tools, and born are hands"--William Blake, 1757-1827


        • #5
          huckleberry - Thought about it last night and this morning James & Jim have the right answer. Unfortunately the question remains will your alternate material work for the cooking floor? If you have cheap access to the material then you could try an experiment.

          James has been using his infrared temp gauge and his "normal" stove-oven to test different cooking stones for pizzas. This is where a lot of cooks started before they decided to build a brick oven. Different materials heats up to a uniform temperature at different rates and more importantly they cool down at different rates. Check out the Pizza Stone Baking sub-forum. I would suggest you set up a controlled experiment and find out how your material of choice works before using it. Another option, that will take a bit of engineering, is to use the material you want for the floor but engineer it in such a way that you can remove it if you have less than average performance from it. This way, with some labour, you can put in a different floor if needed at a later date. Just from the hassle factor I think that is why most, if not all the builders, have used the same fire brick for the floor as well as the dome.