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  • james
    started a topic High Heat Mortar Primer

    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
    __________________

  • UtahBeehiver
    replied
    Any brick mason supply store will have dry powdered clay. It is inexpensive, something similar to HC Muddox will work.

    Leave a comment:


  • Pizzahorse
    replied
    Originally posted by Gulf View Post
    Natural clay would be just fine to use in the home brew. I can find some very clean layers of it where I live. Some streaks of clay will have rocks and organic matter in it. Clay such as that will need a little processing. That can be a little time consuming but, it can be done.
    Thanks, all,

    I have a source for clean clay, Sheffield Pottery in MA.

    So would I just be losing out on the extra refractory qualities then, do we think?

    Leave a comment:


  • Gulf
    replied
    Mk e,

    It is so much easier to make the home brew and not have to "point" an entire dome imo. Also, I'm going to add part of my reply from the oither thread.

    The made from scratch formula (Portland/lime/sand) for general purpose mortar is inadeqate for temps that our ovens reach. It will degrade. But, there is an even worse problem with using premixed masonry cement or premixed mortar. The lime is added for workability in general pupose mortar, not as a refractory. So, here in the states, manufactureres are allowed to substitute part of the lime in the recipe with what the industry calls "or the equivalent". The "equivalent" will usually be crushed limestone and other proprietary additives. This allows the manufactuer to make the product more economically and produce a mortar that is not as caustic. Crushed limestone expands more so than lime when heated. In a fireplace fire box that results in damaged firebrick.

    Leave a comment:


  • mk e
    replied
    Originally posted by Pizzahorse View Post
    Right, so if I just use general purpose mortar, will my structure fall down, or will I just lose some of the refractory quality and not get as hot a cook?
    That's how mine is built, plain $7/bag mortar, but the inside is pointed with the high heat stuff.

    My bother told me that's how he always builds them, it's way easier......but...but.....and after some digging I found this paper that says under 600C it doesn't matter what you use:
    https://info.ornl.gov/sites/publicat...es/Pub1043.pdf

    only the very surface should ever cross 600C, so normal mortar pointed with heat temp it is.

    Leave a comment:


  • Gulf
    replied
    Natural clay would be just fine to use in the home brew. I can find some very clean layers of it where I live. Some streaks of clay will have rocks and organic matter in it. Clay such as that will need a little processing. That can be a little time consuming but, it can be done.

    Leave a comment:


  • mongota
    replied
    Originally posted by Pizzahorse View Post
    Right, so if I just use general purpose mortar, will my structure fall down, or will I just lose some of the refractory quality and not get as hot a cook?
    If you use a portland cement/sand/lime mixture - which is "mortar" - the portland cement can lose some of its structural integrity at the high temperatures seen in a WFO. You could be left with less binder in the mix, and what is left in the firebrick joints can powder away over time.

    Will your structure collapse? Not likely. The dome is built in compression. You could end up with partial gaps between bricks if the mortar does decay, but the dome should maintain its shape. I could see potential issues regarding the structural integrity of a vent arch with compromised mortar, as the arch shape, depending on its geometry and whether is is buttressed or not, may not inherently be a "strong" as a dome. However - the vent arch typically sees lower temperatures than the brick inside the cooking dome.

    Might you occasionally end up with grit in your food from the decaying mortar? It's possible.

    In the end, you can build a dome with basic mortar, but it may not be the best way to build.
    Last edited by mongota; 09-18-2018, 05:14 AM. Reason: spelling

    Leave a comment:


  • Pizzahorse
    replied
    Or what if I use regular clay instead of fireclay?

    Am I being nuts here? Why does nobody else

    Leave a comment:


  • Pizzahorse
    replied
    Right, so if I just use general purpose mortar, will my structure fall down, or will I just lose some of the refractory quality and not get as hot a cook?

    Leave a comment:


  • Gulf
    replied
    Depending on the ratios, just general purpose mortar.

    Leave a comment:


  • Pizzahorse
    replied
    What would happen if I mix Portland cement with sand and lime, but skip the fireclay?

    Leave a comment:


  • Pizzahorse
    replied
    Hi,

    I picked up a bag of heat stop 50, and got super scared by the carcinogen warnings (I think it said to throw out your clothes if they got contaminated).

    What dust precautions should we be taking? Are any of the other high heat mortar methods easier or safer in this regard?

    Leave a comment:


  • shanxk8
    replied
    Maybe I will try dry bricks with just a sponge wipe today .
    and yes, I am using type s lime . Returned the type n the other day and got proper kind .

    Leave a comment:


  • shanxk8
    replied
    Here's an example, they are fire bricks, clean and wetted with a dunk then wipe with sponge. I am using jointing sand.

    It could be that tapping of subsequent bricks in the arch has dislodged earlier bricks. Guess I will have to slow down, the heat stop didn't have the same problem.

    Leave a comment:


  • agrasyuk
    replied
    Originally posted by shanxk8 View Post
    Hi all, I've been trying the 1:3:1:1 home brew mortar with my outer arch today (after using heat stop 50 for my dome). but I am finding that the bricks are not sticking together very well with the home brew. It seems to be setting, just not adhering to the bricks

    Any suggestions?
    Another vote to make sure bricks are clean. While I don't wet the bricks for purpose of them being damp I do wash them throughout - both my angle grinder and radial arm saw leave heavy coat of dust.

    You saying an arch this means you building on some sort of support. Is it completely stationary? Do you have situation where you dislodge fresh already set bricks wile tapping the new ones in?

    Im having a hunch that type of sand may also play a role . Built my oven with "playsand" , was a joy to work with. Now that I'm using masons sand , from a very respected manufacturer I notice mortar behaves worlds apart different as it is sharper.

    In your situation I would probably try and increase water content for bit more sloppy mortar (had to do it for my sharper sand otherwise it lumped).

    Leave a comment:

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