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Post by stefanvh on May 29, 2019 3:02:43 GMT -8
A question with regards to laying the firebricks and the mortar: Is it advised to wet or soak the firebricks before connecting them with fireclay/sand mortar? I've read somewhere that the absorption of the water/clay mixture creates the strong bond (and thus the bricks should be dry)? For cement the quick absorption won't work but I can't really find any other info on fireclay/sand mortar.
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Post by josephcrawley on May 30, 2019 7:33:02 GMT -8
I have never soaked my brick unless it was stored outside and had recently rained.
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Post by stefanvh on Jun 4, 2019 5:52:35 GMT -8
So I tried soaking, more sand, more clay, a thick layer, a thin layer but nothing seems to really stick two bricks together. It sticks initially, but the bricks are easily separated even after the mortar has dried... Any tips, or is this expected (someone mentioned that it is to keep the bricks apart and fill up the gaps and not keeping the bricks together), and if so, how do you build a sturdy construction? Just a dry stacked wall is easily tipped over.
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Post by martyn on Jun 4, 2019 8:08:48 GMT -8
Using a clay slip (liquid clay) is a standard way to seal or bed bricks together but it won’t make a strong bond.. even less so when super heated. I can’t think of anyway to permanently bond fire brick in a high heat situation. The clay slip will work for most rocket stove builds, if you are very concerned then consider using refactory casting cement and make a mould. There Is another way of bonding the bricks by using “home brew refactory cement” this is the standard mix for building brick pizza ovens domes. It is a formula of Portland cement, clay and lime but it is designed to fill the back of the bricks and not actually exposed to flames . Home brew will give a strong bond but it will release on one side of a brick due to the bricks expanding and contracting with the heat.
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Post by patamos on Jun 4, 2019 8:34:37 GMT -8
portland cement with added alumina powder can work in a pinch. Otherwise store-bought 'furnace cement' which is basically sodium silicate with talc powder.
There is also something to be said for 'non-setting' mortars. IN other words, rely on the structure to keep the bricks in place rather than the glue. They are going to want to keep moving over time any way...
my 2c
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Post by stefanvh on Jun 4, 2019 9:58:54 GMT -8
Thanks. I've read before that the mortar should have some flexibility to cope with expansion during high temperatures, but I expected to at least have some bonding strength. I glued some red clay bricks together with some dug up soil and that seemed to work fine (i.e. I glued two of them on top of each other and could pick up the top one without the lower one coming loose, similar to this: www.youtube.com/watch?v=EFnWnlCLsEw). With some force they can probably be separated but it was good enough. The fireclay and firebricks however didn't seem to stick at all. I think I found the culprit. This is a ball made directly from the bag of pure fireclay: www.dropbox.com/s/dbo8bomypdi5xr5/20190604_192934.jpg?dl=0I'm no soil expert, but I am pretty sure there is (quite some) sand in it. Anyway, we decided to use refractory mortar. The 'fireclay' for sure didn't work at all, and the rest here is convinced it should be able to withstand throwing large logs of wood in it, so the mortar should provide that strength. Probably not the best solution to prevent cracks/leaks, but not much other choices at the moment. A collapsed firebox wall inside the bell would be a bigger problem.
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Post by wiscojames on Jun 4, 2019 10:37:08 GMT -8
If you end up using a clay based mortar, try adding some fine wood ash. I've found that it makes the mortar stickier.
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Post by patamos on Jun 4, 2019 14:59:17 GMT -8
ya wood ash for sure.
I've also had a terrible time using lincoln fireclay to bond common firebrick. The bricks are so porous they suck the joint dry too fast. If you put one in a bucket of water you can hear it sucking in moisture for a loooooong time. Total sponge...
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Post by stefanvh on Jun 14, 2019 5:19:12 GMT -8
I also tried dipping the sides in pure clay slip, but after it dried the clay just flakes off. The edges of the bricks feel as if they have been polished. I think soaking might help as the dry brick may immediately form a dry layer of clay when dipping. I'll try that later.
Building is finished (with refractory mortar). I'll create a thread in the finished subforum later after everything is complete.
Edit: Soaking didn't help either, at all. I think the water is actually keeping the bricks together. When dry, there seems to be zero adherence of the clay to the brick. The bricks probably need to be somewhat porous to the clay.
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