32" build in Calgary, AB - pompeii neapolitan

[david s]

Although there have been many successful brick galleries built and traditionally it is the method used, a cast refractory or stainless gallery have more advantages, both in reducing thermal mass, structural integrity and being better to adapt to curves easily.

Brick units are not ideal because they have two big drawbacks. Firstly it adds a lot of thermal mass in an area where you don’t really need or want it. Secondly, brick units introduce instability. because of the many mortar joints, introducing weak points from thermal expansion and contraction.
Also an inverted arch as in the second drawing is inviting expansion rather than compression.
Anchor plates usually call for drilling holes and using fixings, both of which can lead to areas where cracks develop. Using an alternative method to fit or omit one is worth considering.

[IH123]

Although there have been many successful brick galleries built and traditionally it is the method used, a cast refractory or stainless gallery have more advantages, both in reducing thermal mass, structural integrity and being better to adapt to curves easily.

Brick units are not ideal because they have two big drawbacks. Firstly it adds a lot of thermal mass in an area where you don’t really need or want it. Secondly, brick units introduce instability. because of the many mortar joints, introducing weak points from thermal expansion and contraction.
Also an inverted arch as in the second drawing is inviting expansion rather than compression.
Anchor plates usually call for drilling holes and using fixings, both of which can lead to areas where cracks develop. Using an alternative method to fit or omit one is worth considering.

Thanks for the reply. however , I already purchased additional mortar and bricks to build the arch. I am avoiding castable refractory because casting isn't always better. A cast refractory must be allowed to dry and cure properly and I have no experience in that- thermal expansion still has to be accommodated with rigid cast tied tightly to refractory bricks tightly can crack too. I am looking to choose a brick arch. I am going for now, unless someone tells me about a better brick arch design, with the inverted arch because I am planning to create a concrete buttress for the arch (regular concrete not refractory concrete) and separate the arch from the concrete buttress using leftover CaSi and/or Ceramic Fibre boards - I believe having a rebar reinforced concrete pillar buttress will create a very well solid support for the chimney and the full archway especially its not connected to dome , it will allow me to go higher .

[IH123]

I today completed the dome, and the inner arch was already complete. the dome ended up about 13.5" high instead of 14 1/8", I did not use trammel for top courses and likely mortar was thicker than planned and brick cuts might have been not exact. The dome top stone brick wasn't like you expect like a polygon on or anything like it,I jut used regular dome brick cuts and fit them in anyway that reduces mortar thickness to be between 3mm-9mm (my mortar specification/ requirement) - ended up a dump of bricks however they are tapered so they got locked without mortar (however mortar was used). here are the pictures:

[IH123]

and I believe I will proceed with the following for the remaining arches. as originally planned: inverted arch for flue gallery (6-6 1/4" deep) and segmented arch for mouth arch (~3" deep) however will as planned have a buttress as shown below:

[IH123]

The flue arch was built, however the right leg got dislodged - a set back. I built the right leg and the arch in same session and the mortar of the legs had more water than usual so the top brick of the leg (shown in pencil flash marks in picture) was pulled outwards- I did not know it until I finished building the whole arch. I removed the right leg and arch part( as on big piece) and let it cure while sleeping on its side and scrapped the uncured mortar from the single brick faces. I will re-mortar the full right arch and leg half one large piece at the detached brick tomorrow: when I was pressing the bricks on the left part they dislodged the workform causing the over watered mortar on the right arch leg to pull up or the weight of the bricks pushed the soft mortar out and up. pictures before I removed the right part:

[IH123]

I am planning to abandon the fibre glass rope and fill the gap between inner throat arch and the flue arch with crushed perlite+thermobond 915 at 1:3 mix ratios instead of fibre glass or ceramic fibre rope. will aim for about 1.5" thick bead of that paste on the outside. This would bridge the gap between the dome and the archway without heat loss

[david s]

I presume your intention to use an insulating mix to join the gallery to the dome is driven by a desire to thermally isolate a very heavy heat sink that wants to drawi heat from the dome. If so, be aware that adding an insulating material to a mortar will drastically reduce its strength. The thickness of the material also plays a big part to how much it will slow conductive heat transfer. The thicker the material, the greater the effect. Because your mortar is recommended to be only applied very thinly, you may end up with a failed result.
I use blanket sealed at the top with homebrew cut with fine vermiculite as an insulating material to protect and separate gallery and outer decorative arch by an 8mm gap, but the homebrew mix is good for thick joints. Also the end result will not be elastic. The reason some builders use the rope is because it provides elasticity.
If you want to invent a mix, test it for strength first.

Heere's a table on insulating mixes their insulating values and strength that might help you

[IH123]

I presume your intention to use an insulating mix to join the gallery to the dome is driven by a desire to thermally isolate a very heavy heat sink that wants to drawi heat from the dome. If so, be aware that adding an insulating material to a mortar will drastically reduce its strength. The thickness of the material also plays a big part to how much it will slow conductive heat transfer. The thicker the material, the greater the effect. Because your mortar is recommended to be only applied very thinly, you may end up with a failed result.
I use blanket sealed at the top with homebrew cut with fine vermiculite as an insulating material to protect and separate gallery and outer decorative arch by an 8mm gap, but the homebrew mix is good for thick joints. Also the end result will not be elastic. The reason some builders use the rope is because it provides elasticity.
If you want to invent a mix, test it for strength first.

Heere's a table on insulating mixes their insulating values and strength that might help you

Thanks for the tip however Thermobond 915 can go up to 9mm thick on its own. my gap is 1/4" only, well with in the range. Portland cement water bound when mixed with perlite gets destroyed at much lower temperature than Thermobond 915. 500c vs 1400c. the inner throat arch will have flames(> 1000F) that well exceed what Portland cement is designed for(300-500c) and thus will not hold anything for long. Thermobond 915 is rated for 2550F and is the best for it, though more expensive. yes, I am making an insulation and seal mix that is not structural so will not hold any thing more other than brick fast expansion and contraction

[IH123]

I managed to fix the broken right flue arch part, I found that balancing it with certain amount of counter weight will make it set by itself plumb so that allowed me to remove the form and let it cure free standing. I will measure up front all the remaining central weight of chimney (which will be added later) and divide by half and try to add counter weights on each side so that the arch will be self balanced and stable standing on its own, I will still buttress on the outside and have ss rod on the inside however I will not drill into the brick, I rather will carve using an angle grinder a channel between two courses of bricks and lay out ceramic fibre paper nest on which the ss rod will set and then mortar everything to form a rod between the arch opening to prevent it collapsing inwards,outside buttress would be to prevent collapsing outwards, and counter weight will ensure it has no static push to any side such that supports are only for dynamic forces: