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

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  • timo
    replied
    Re: High Heat Mortar Primer

    Karl, thanks for that info. I am right at that point of arch opening to dome. The cuts there are pretty time consuming and baffling. I am trying to keep the brick pieces as large as possible, but there are some smaller ones placed in a thicker than normal mortar gap. Be glad when this part has passed.

    From many previous posts I have understood that the large gap(the wedge) on the OUTSIDE of the brick is OK because it doesn't receive a straight dose of heat. I have been trying my best to snug the brick edges together so the gaps on the inside are very small.

    Would it be acceptable to say that home brew mortar should be at least 1/8th" thick, but not more than 1/2" thick?

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  • karl
    replied
    Re: High Heat Mortar Primer

    It is not really the mortar which keeps the bricks from falling in. It is the lining up of the bricks in a certain diameter. If all bricks keep their position and there are contact points between each bricks and it's neighbour bricks (in 2D) the rings should not collapse. But often there are certain areas (in particular in the transition between the oven and the opening) where there are voids which have been filled with mortar. If such mortar disintegrate the ring of bricks may collapse.

    karl

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  • Mierkmike
    replied
    Re: High Heat Mortar Primer

    I made up my refractory morter using the 1113 mix. I was later told by another oven builder that the Portland cement will disenagrate at 600 degrees and the bricks will get loose and fall in. Has anybody experienced this?

    Leave a comment:


  • Lars
    replied
    Re: High Heat Mortar Primer

    Timo,

    Yes, I have posted many times about my ( I am pretty sure) success with my wonderful mortar recipe -- 3:2:1:1/2 ( Fine Sand, Fire Clay, Portland, Lime) I have started my first curing fires and do not have anything more to report at this time. So far I still REALLY like the mortar I used, but I haven't gotten anywhere near totally up to temperature. It's so hot, it may be a week before I continue with the curing/insulation.

    I suspect that the high dollar mortar manufacturers pushed through regulations to force people to buy their stuff. ( just conjecture with no basis in fact that I am aware of)

    Great price on that fire clay, by the way. I think I paid $25 for a 90lb. bag, but someone had brought it up special from another state. I am finished and won't be needing much of the 50lb. bag I have left. I have been mixing it into my (regular) brick mortar for a little light brown color.

    Lars.
    Last edited by Lars; 06-23-2009, 09:41 AM.

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  • timo
    replied
    Re: High Heat Mortar Primer

    I just picked up 4 50# bags of fireclay from Clay Products in Spring Grove, Illinois. They were $11.40 a bag. I plan on using the mix your own method.

    I have found many brick yards want to sell you the Heatstop for $74 instead of the 100% fireclay. Could be due to newer construction rules? Anyway, are there any more reports out there from home brewers and their results?

    Thanks,

    Timo

    Leave a comment:


  • RTflorida
    replied
    Re: High Heat Mortar Primer

    Fire clay is a specific type of clay with the same refractory characteristics as firebricks.
    It has an unusually high content of alumina (24% - 40%) and an overal alumina/silica content of 55%-60%.
    Although naturally occuring and found all over the world, there is no way for any of us to judge whether the soil around your home contains fireclay. You may simply have "pain in the ass, I can't dig a whole" clay. If you are serious about using materials found around your home, I would research exactly what the characteristics of fireclay are in nature.
    The cheapest and easiest solution is to go to a pottery, refractory, or brick supplier. Fireclay is cheap around here, it is $5 for 15 lbs or $15 for 40 lbs, depending on the supplier.

    RT

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  • Abear
    replied
    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?

    Leave a comment:


  • Lars
    replied
    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.

    Leave a comment:


  • Dutchoven
    replied
    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

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  • tdibratt
    replied
    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.

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  • david s
    replied
    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.

    Leave a comment:


  • tdibratt
    replied
    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

    Leave a comment:


  • david s
    replied
    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.

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  • brokencookie
    replied
    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

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  • karl
    replied
    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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