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

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  • JRPizza
    replied
    Great advice! Bricks being too wet gave me some adhesion problems early in my build. I learned to just hit the edges with a damp sponge enough to wipe of any residue from cutting and to see the moisture suck in about a quarter inch or so. With the right consistence of mortar the dry(ish) bricks will really "grab" onto it.

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  • wotavidone
    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?
    Aaand......here goes the great wet/dry debate.
    Are they firebricks? Are they clean? Are they wet or dry?
    Did you use proper hydrated lime - NOT agricultural lime from the garden shop?
    I belong to the clean and dry school, I think. Until next week when I might change my mind.
    My thinking is that a clean, dry, hopefully slightly porous brick will suck some of your lime loaded water from the mortar into the brick and help greatly with adhesion.
    I washed my bricks and let them dry out for a while. Of course in summer, on a hot day a completely dry brick might suck too much water out of your mortar and screw it up so ypu might want your brick damp rather than completely dry.

    The lime must be slaked lime or hydrated lime. i.e calcium hydroxide.
    This stuff will combine with carbon dioxide from the air to form calcium carbonate (lime stone) in situ, thus binding your aggregates together and taking the place of the mix of calcium silicates in the Portland cement that may eventually decompose from the heat.

    Lime from the garden shop is probably crushed limestone, calcium carbonate. Won't undergo the carbonation reaction, because it already has, so won't contribute any set/adhesion/strength to the mortar.
    Last edited by wotavidone; 06-08-2018, 07:16 PM.

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  • shanxk8
    replied
    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?

    Leave a comment:


  • Campmaki
    replied
    Hello from frosty Wisconsin, I had very good luck with using a home brew mortar. My quantities were, 3 parts silica sand, 1 part lime, 1 part cement, 1 part fireclay. I used a paddle on a electric drill to mix. Mix only the amount you will use in a short time, as it sets fast. I dry mixed before adding water. My posts/ pictures are under Campmaki, hope this helps.

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  • Brad Low
    replied
    Hi
    Looking for some advice. We've found a product at Bunnings in Oz which is a premix of sand, cement and hydrated lime https://dingocement.com.au/product/m...ix-handy-pack/ We called Dingo and they let us know the ratio is 3-4 parts sand: 1 part cement: 1 part lime. We're adding 1 part fireclay to this for our mortar. Can anyone see any issues with using this product that we haven't realised? Or has anyone used this product?
    Cheers
    Brad

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  • karl
    replied
    Re: High Heat Mortar Primer

    CaMaHa7

    Is it correct that you plan to cast your dome and not use bricks with high heat mortar in between?

    I have no experience in casting a pizza oven dome. But I would be very hesitant in doing so without a structural reinforced concrete dome. Dense high heat castablel concrete may good (I do not now), but you should consider reinforcement by using iron reinforcement. Refractory cast needs to cure and sinter at the right temperature to obtain strength and I am not used to think of such a concrete as a structural layer. But I am not an expert here.

    I guess the dome diameter and diameter/height ratio comes in as a parameter. Unless this is a very small build I would consult someone who has done this before.

    Karl

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  • CaMaHa7
    replied
    Re: High Heat Mortar Primer

    Hi there,

    I am building my pizza oven at present and just planning the Dome structure.

    I purchased Dense Castable (up to 1400c temp), which the supplier advised to simply mix with water to a peanut butter consistency (3 x 25kg bags).

    He advised to cover my sand formed dome with wet paper and then to cover this with the castable mix.

    I am then going to create layers of fireclay mortar, then fireclay with wood shavings and an outer layer of fireclay mortar with perlite added.

    For the mortar, I will follow the 1:3:1:1 ratios.

    My question is, will the castable mix hold the weight of the clay which will be create the walls of 20cm thickness?

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  • cobblerdave
    replied
    Re: High Heat Mortar Primer

    G'day
    If at all possible use firebrick for the hearth, they'll handle the heat better. If not commons ar'nt twice there width to there length to allow for a mortar gape. Don't use herringbone pattern the gapes will be too big. Lay the floor at 45 degrees to the entrance and you'll be right
    Regards dave

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  • FrankHawkins
    replied
    Re: High Heat Mortar Primer

    Also interested to hear what time scale your referring to. I can't afford firebricks so had to use the old red clays that I have. I've read in many places that they are a fine alternative to fire bricks. Seems to be mixed views about them. The cost has mounted up so much more than I thoughf when I started this project I have no option other the the old red clays so really hoping that they hold up to the job! Lol

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  • Volongo
    replied
    Re: High Heat Mortar Primer

    Originally posted by Campmaki View Post
    for an oven that lasts use firebrick.
    Campmaki, What do you mean for an oven that lasts? What time frame are you referring?

    Leave a comment:


  • GianniFocaccia
    replied
    Re: High Heat Mortar Primer

    Don't waste your money on high temp mortar
    +1

    Homebrew all the way.

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  • Campmaki
    replied
    Re: High Heat Mortar Primer

    Originally posted by FrankHawkins View Post
    Hi guys. I have a query on what people have found best to work with.
    I have found a ready mixed high temp cement from a wood burning oven specialist. He also sells dry cement to just be mixed with water. Both rated to 1600.
    However it says that it should be applied between 2-5mm.
    What have people found best to use?
    The lime, fireclay, cement and sand mix or these specialist high temp cements?
    I'm in really split minds and am very unsure which way to go?
    I'm building my dome with old red clay bricks.
    Interested to hear people's reaponses and how you guys have done it?
    Don't waste your money on high temp mortar if you are using red clay brick. You should be using medium grade firebrick, not a clay brick. You can but for an oven that lasts use firebrick. Do some research on the proper materials to use.

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  • Tscarborough
    replied
    Re: High Heat Mortar Primer

    This question has been answered dozens of times, several in this thread. Search around a bit.

    Leave a comment:


  • FrankHawkins
    replied
    Re: High Heat Mortar Primer

    Hi guys. I have a query on what people have found best to work with.
    I have found a ready mixed high temp cement from a wood burning oven specialist. He also sells dry cement to just be mixed with water. Both rated to 1600.
    However it says that it should be applied between 2-5mm.
    What have people found best to use?
    The lime, fireclay, cement and sand mix or these specialist high temp cements?
    I'm in really split minds and am very unsure which way to go?
    I'm building my dome with old red clay bricks.
    Interested to hear people's reaponses and how you guys have done it?

    Leave a comment:


  • LiamK
    replied
    Re: High Heat Mortar Primer

    On "oldie but goodie" topic.

    1) I'm curious if the order of mixing the ingredients matters, and if so why? (I just want to learn a little more about the chemistry or physics or practicalities of it.)

    I would have thought to mix the finest-grain ingredients together first (Portland cement, fireclay, and lime), and only after they are mixed then mix in sand. Sort of like sieving together the flour and baking-powder first, in a cake mix. But the list of ingredients (1:3:1:1, as in 1 part Portland cement, 3 parts sand, 1 part lime, 1 part fire clay) and what I've read elsewhere suggests mixing the sand and cement together first, and then adding the lime, and the fireclay last.

    2) Sand: how "fine" is fine-grain? Let's talk mesh (size of grains). Is #50 fine enough? Is #80 better, or is it too fine? #120? The latter seems like powder, to me. It is available where I live down to #400 mesh, which is a very fine dust like kaolin powder; even finer particles are available for specialized purposes. ("Mesh" refers to the size of the opening the grains will fit through, when sieving.)

    3) Also, how much water to add? This seems to be left out of the recipe mixes. Perhaps the various videos or pics tell this better than words, to get the right consistency. I used to think that the less water the better (within reason) for strength, as this is what I learned using Quikrete in driveways (non-refractory application, of course!) -- too much water weakens it. But some experimentation quickly revealed that too little water is also a problem in making refractory mortar, the mix never really adheres to itself, doesn't hydrate/cure enough or right, and is very weak and crumbly. (Even if one could form a ball that held together after pressing it in your hands, that wasn't wet enough -- it needed more water.) Like Goldilocks and porridge, I guess it has to be "just right": well-mixed, not to dry and not to wet.

    If the order of mixing isn't important, would it help to mix the cement/lime/fireclay first, then (separately) add water to the sand and then mix the wet sand with the dry ingredients, to help spread the moisture around?

    Just brainstorming, to learn from the pros on here. :-) Many thanks to those who really know, for sharing your insights here!)

    Leave a comment:

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