36" build in heart of Europe, Czech Republic

[mrotter]

I was fortunate in that my bricks were flat and had parallel tops and bottoms, so all I had to do was sort for similar thickness and laid them on my CF board without needing anything to level them out. If I were in your situation, I would do a similar sort to get enough uniform/similar bricks to build the floor. Set those bricks with the best face down on a flat surface and knock off any irregularities with an angle grinder or similar tool to get a relatively flat smooth underside surface. Flip them over and lay your floor - use a leveling mix if you still need it - lots of posts on how to mix and level a floor.

Despite my firebricks are reclaimed, they basically are of uniform size which is standard in our country - 25*12.5*6.5 cm. Some of bricks are scratched or their corners broken off etc. which makes building process quite slower. I believe if I had brand new nice bricks, things would go and especially look nicer.

That said I so far spent very little money even when I bought professional aluminate mortar, CaSi board etc.

I believe that so far I've spent less than 400 USD and will very likely spend less then 500 USD in total:

- bricks (150 pcs, reclaimed) - 80 USD
- CaSi - like 120 USD
- mortar - 80 USD
- base red bricks - basically free (reclaimed)
- insulfrax insulation to cover dome - 10 USD (four large boxes, much of it will left) - I bought it as "leftovers" from big local company which builds large furnaces
- some minor material like 50 USD so far
- hearth concrete - like 70 USD maybe

Things to buy at this point:
- some concrete bagged mix to cover dome insulation (I already have vermiculate which I will add)
- bag of fireclay (part will be used under floor bricks, part will I add to dome enclosing concrete layer)
- bag of silicone (or acrylic) final render (will be bought from neighbor who builds houses for living, some leftovers almost for free)
- fire-resistant rope

Yesterday I was talking to my father-in-law who is professional structural engineer. He does exactly calculations of the structural stuff used in ovens basically - arches, horizontal/vertical forces etc. He did some basic calculations and found out that basic axe-like arch of my dimensions, only standing on bricks in their 12.5 cm side with NO buttressing should carry HUGE chimney/vent constructions without any problems.

Here are some pics from weekend's work. I was little unsure about my dome-arch transition so had to backfill some space with pieces of bricks but I realized how it should look/connect - you either cut arch bricks and create surface on which dome bricks sit, or you cut dome brick to make it sit to arch brick or combine both approaches - which I will partly do to "interlock" those two structures well. I will complete 5th (basically) course intersection likely today. I also started to observe inverted V-shape in dome bricks, so decided to "bevel" their corners a bit with angle grinder to redice the V. Also, I backfilled all big mortar sections with firebrick scraps.

So far so good. My work is far from looking nice and tidy and clean like builds of masters from this forum, but things are going forward nicely. I do not rush anywhere.

[mrotter]

More photos.

[mrotter]

I imagine you can, but I'd give some thought to a courser sand, which may stay in place better and maybe mix it w/some fireclay. I'd also use as little as you have to, as I'd have concerns w/it shifting over time. If it's not too much, it's probably not a real issue. Hopefully, your bricks will allow you to still have a nice flat floor. Nice progress!

Thanks, OK. I would likely need to buy fireclay 25 kg bag, sadly it seems they do not sell smaller amounts here.

[david s]

Structural engineers are unlikely to take into consideration the considerable thermal expansion (around 5mm) and subsequent contraction on cooling. If this is experienced day in day out it is likely to test the structural integrity of an unsupported large radius arch, particularly if a large mass, like a brick chimney is sitting on top of it. This is one of the reasons oven designers opt for a far lighter stainless flue pipe.

[mrotter]

Structural engineers are unlikely to take into consideration the considerable thermal expansion (around 5mm) and subsequent contraction on cooling. If this is experienced day in day out it is likely to test the structural integrity of an unsupported large radius arch, particularly if a large mass, like a brick chimney is sitting on top of it. This is one of the reasons oven designers opt for a far lighter stainless flue pipe.

You might be partially right. Definitely not saying you are wrong.

Once I get to that stage of building oven vent, I will have to make a decision. We will see.

edit: I definitely plan to use relatively lighter chimney solution.

[mrotter]

Some photos.

Still struggling a bit with angles/dimensions of inner arch, but decided to cut lower angle/curve as it is defined clearly by ID of the dome and IT helped with it.

[mrotter]

I am but puzzled about "top side" of arch bricks - the side on which relevant dome brick will sit. How can I determine how "deep" inside the arch brick should the cut be?

See pic: https://imgur.com/a/OFnppcx

Which line? How do I know?

JRPizza
UtahBeehiver

[NCMan]

It may be just different terminology, but you do not want to use bagged concrete mixed w/vermiculite over the dome. You want to use Portland cement w/it. Also, there would be no use in using fireclay outside the dome. You may want to discuss all your planned layers.

[Gulf]

I am but puzzled about "top side" of arch bricks - the side on which relevant dome brick will sit. How can I determine how "deep" inside the arch brick should the cut be?

I hope that this link helps. Your arch is more hemispherical but, it is the same concept.

[JRPizza]

In addition to Joe's link above, UtahBeehiver showed a picture in post 61 of this thread and I use the attached picture to kind of show what the TDC brick can look like. If I moved my brick further away from the center of the oven the intersection of the ID and the top angle would move downward with the extreme being only the rear lower point of the brick touching the ID. I tried to go for the intersection being somewhere in the middle of the TDC brick, if that makes sense.

[mrotter]

It may be just different terminology, but you do not want to use bagged concrete mixed w/vermiculite over the dome. You want to use Portland cement w/it. Also, there would be no use in using fireclay outside the dome. You may want to discuss all your planned layers.

Terminilogy things.

I believe that in all countries "concrete" is basically - portland cement + sand + (potentially gravel) + water.

What I want to you to enclose dome insulation is - portland cement + touch of sand + perlite + water + touch of fireclay + touch of hydrated lime. I have quite a bit of experience with concreteing. The above mix as kind if similar to "homebrew" except amounts of fireclay and lime are much smaller in my mix. It is basically concrete with bit of extra elasticity (thanks to fireclay) and bit more heat resistant (thanks to combination of fireclay and lime). I understand that temperatures outside of insulation will not be high, but just to be sure.

Thanks.

[mrotter]

I hope that this link helps. Your arch is more hemispherical but, it is the same concept.

That helped massively. I also am now assured that ID line on my arch bricks is sort of correct.

Thanks. I will try to scribe OD line with assistence of my tool to have better understanding on the angle of the cut.

[mrotter]

JRPizza Thanks, helped too.

[david s]

This table may help you. You can make it as strong or as weak as you like, but as the table shows, if you make it stronger you reduce its insulation value. For over the dome to restore the hemisphere form i like to also get a decent insulation value out of that layer so I make it pretty lean (10:1), which is about the same insulation value as blanket, but much cheaper and also firm enough as a substrate for a cement render.

If adding perlite to a cement render you will reduce its strength (as the table shows) as well as adding permeability. My own view is to make the outer shell thin, but strong so I don't use a mix with either perlite or vermiculite and I do also add random reinforcing fibres. Some builders prefer a thicker outer shell that does contain perlite or vermiculite. There are different approaches.

[mrotter]

This table may help you. You can make it as strong or as weak as you like, but as the table shows, if you make it stronger you reduce its insulation value. For over the dome to restore the hemisphere form i like to also get a decent insulation value out of that layer so I make it pretty lean (10:1), which is about the same insulation value as blanket, but much cheaper and also firm enough as a substrate for a cement render.

If adding perlite to a cement render you will reduce its strength (as the table shows) as well as adding permeability. My own view is to make the outer shell thin, but strong so I don't use a mix with either perlite or vermiculite and I do also add random reinforcing fibres. Some builders prefer a thicker outer shell that does contain perlite or vermiculite. There are different approaches.

This is amazing, thanks.