37" Pompeii Build, 2nd Half - forum assistance needed!

[Whackers]

Finally, I am taking the plunge and asking for help in the forum, rather than just absorbing the amazing information here for everyone.

I am hoping that, having got about half way through my build, I can lean on the experience and support of this community to help me avoid any sizeable mistakes, and aware that this is when it gets a bit tricky!

I've got to a stage where it is now, hopefully, all about the build of the dome (and the insulation underneath/around it); each day I seem to come up with more questions, than answers to the previous days' questions so here's where I can share and benefit from your cumulative knowledge.

I need to resize some more photos in order to upload them under this topic (or more likely set up an album) and bring them to life but I will start with a dump of the current situation and questions and a few images of where I am right now.

I've built the concrete base structure on which to build the dome, the intention is that the dome will be 36-37 inches internal diameter...(I am just measuring that out and not worried if it is one or the other, just want top make optimum use of the space available.) I've bought most of the material that I thought I needed from a Kiln company, to save money primarily, and so some of the materials I have bought will not be perfect, but I am hoping that without too much further investment, I will be able to complete the build without compromise and with an oven that functions pretty close to perfect and I can be proud of.

Things I know I need to do fairly soon (please excuse any poor descriptions or using the wrong names for things!):

1. Drill 2 or 3 holes beneath the concrete oven to allow for any water under the insulation to escape and fix mesh on the underside of the hole in the concrete slab
2. Lay mosaic tiles - based on what I have read across the forum - across the footprint of the oven
3. Measure, cut and lay the oven floor fire bricks using a circular template to determine most efficient use of bricks then cut the same dimensions in insulation board to lay under the fire bricks
4. Not lay the first layer of dome bricks in the orientation you see in the photos, but to lay them as soldiers
5. Jigsaw the inner plywood for the oven and fix the IT to the centre of it. (IT is nearly built)
6. Build the forms to support the two arches (below question on dimensions of the two arches will determine that)



Questions I need to answer relatively soon (there will be plenty more):

1. For a 37 inch (94cm) oven, with a likely internal height of 19 inches (48cm) when it is built - what height and width should the oven door and outer door be?
Inner - My initial research suggests inner oven door (*the one effectively built into the dome structure) should be c.62% of dome height so 11 and 3/4 inches (30cm) and the width is less critical but should be about 18 inches wide.
Outer - which I will build out of fire bricks could simply be 2 inches wider (20 inches) and 1 inch taller - this in effect creates the seal for any door I construct to be inserted and pushed up against the inner oven door/arch and rest against a sufficient 1 inch 'lip' of firebrick. The distance between the inner and outer arches is likely to be c.400mm - between one and a half, and two bricks (length-wise) depending on the final room I have to the front of the concrete plinth.

2. After the mosaic tiles, I have Calcium Silicate board (melting point 1345 degrees celcius) 230-290 kg/metre cubed bulk density. Then I was intending on laying the firebricks on top of the Calcium Silicate (with some building sand to enable the best level and fit for the fire brick floor). The board is 50mm deep. My question here is do I need any additional layers between the main Concrete slab (*and mosaic tiles for drainage if water gets underneath the Cal-Sil board) some builds I have seen use the vermiculate concrete mix at this point and add another 50mm on top of the cal-sil board, before then adding the sand and fire brick floor...?

3. I have a choice of using a deeper firebrick for the floor of the oven, should I do so, or use the same slightly shallower fire brick (I probably have enough of both so it is an open choice at the moment)? The depth options are "Firebrick 42GD -230 x 114 x 64mm" (the deeper ones) or "Firebrick 42GD -230 x 114 x 52mm" my preference would be the thicker ones for heat retention but likely a slower heat up time. Is this a correct assumption?

4. For the concrete/mortar to fix the dome half-bricks in place, I have bought two products and I'll be honest, I didn't do my research on suitability so know that they won't be perfect here's what I've got... Firstly, Castable - C1400, Secondly I have 60GD HS Cement. Can I use one or both of these castable and/or cement options to secure the bricks in the dome effectively?
(I am aware there is the conventional and heavily recommended 3-1-1-1 mortar mix which I could have opted for (and may yet have to!) although in the south of London I've not found a local place to buy fire-clay yet so hoping I can use what I have. )


Requests for clarity, and then any help, guidance or corrections-before-the-event all greatly appreciated and taken in the spirit intended! I'll set up a photo album to better tell the story of how I have arrived to this point very shortly.


Tim.

[Neil.B]

Not got any comments to your post but just checking you have calculated your plywood base correctly. You have it cut in to quarters, but have you checked you will be able to get it out once built?
I'm up to the same point as you and was considering cutting the template length ways and tape together, so I could just fold them over to slide out of the entrance.

Looking forward to your build, good luck.
Neil

[Whackers]

At the moment the plywood base is there to enable me to gauge where the soldier bricks will sit and then where the calcium silicate board needs to be. With the markings *(It is marked in quarters, but not cut) I am yet to decide whether to leave it in or secure.my IT to the fire bricks. If I do leave it in, it will eventually burn out so I won't worry about that yet.

[Chach]

Finally, I am taking the plunge and asking for help in the forum, rather than just absorbing the amazing information here for everyone.

I am hoping that, having got about half way through my build, I can lean on the experience and support of this community to help me avoid any sizeable mistakes, and aware that this is when it gets a bit tricky!

I've got to a stage where it is now, hopefully, all about the build of the dome (and the insulation underneath/around it); each day I seem to come up with more questions, than answers to the previous days' questions so here's where I can share and benefit from your cumulative knowledge.

I need to resize some more photos in order to upload them under this topic (or more likely set up an album) and bring them to life but I will start with a dump of the current situation and questions and a few images of where I am right now.

I've built the concrete base structure on which to build the dome, the intention is that the dome will be 36-37 inches internal diameter...(I am just measuring that out and not worried if it is one or the other, just want top make optimum use of the space available.) I've bought most of the material that I thought I needed from a Kiln company, to save money primarily, and so some of the materials I have bought will not be perfect, but I am hoping that without too much further investment, I will be able to complete the build without compromise and with an oven that functions pretty close to perfect and I can be proud of.

Things I know I need to do fairly soon (please excuse any poor descriptions or using the wrong names for things!):

1. Drill 2 or 3 holes beneath the concrete oven to allow for any water under the insulation to escape and fix mesh on the underside of the hole in the concrete slab
2. Lay mosaic tiles - based on what I have read across the forum - across the footprint of the oven
3. Measure, cut and lay the oven floor fire bricks using a circular template to determine most efficient use of bricks then cut the same dimensions in insulation board to lay under the fire bricks
4. Not lay the first layer of dome bricks in the orientation you see in the photos, but to lay them as soldiers
5. Jigsaw the inner plywood for the oven and fix the IT to the centre of it. (IT is nearly built)
6. Build the forms to support the two arches (below question on dimensions of the two arches will determine that)



Questions I need to answer relatively soon (there will be plenty more):

1. For a 37 inch (94cm) oven, with a likely internal height of 19 inches (48cm) when it is built - what height and width should the oven door and outer door be?
Inner - My initial research suggests inner oven door (*the one effectively built into the dome structure) should be c.62% of dome height so 11 and 3/4 inches (30cm) and the width is less critical but should be about 18 inches wide.
Outer - which I will build out of fire bricks could simply be 2 inches wider (20 inches) and 1 inch taller - this in effect creates the seal for any door I construct to be inserted and pushed up against the inner oven door/arch and rest against a sufficient 1 inch 'lip' of firebrick. The distance between the inner and outer arches is likely to be c.400mm - between one and a half, and two bricks (length-wise) depending on the final room I have to the front of the concrete plinth.

2. After the mosaic tiles, I have Calcium Silicate board (melting point 1345 degrees celcius) 230-290 kg/metre cubed bulk density. Then I was intending on laying the firebricks on top of the Calcium Silicate (with some building sand to enable the best level and fit for the fire brick floor). The board is 50mm deep. My question here is do I need any additional layers between the main Concrete slab (*and mosaic tiles for drainage if water gets underneath the Cal-Sil board) some builds I have seen use the vermiculate concrete mix at this point and add another 50mm on top of the cal-sil board, before then adding the sand and fire brick floor...?

3. I have a choice of using a deeper firebrick for the floor of the oven, should I do so, or use the same slightly shallower fire brick (I probably have enough of both so it is an open choice at the moment)? The depth options are "Firebrick 42GD -230 x 114 x 64mm" (the deeper ones) or "Firebrick 42GD -230 x 114 x 52mm" my preference would be the thicker ones for heat retention but likely a slower heat up time. Is this a correct assumption?

4. For the concrete/mortar to fix the dome half-bricks in place, I have bought two products and I'll be honest, I didn't do my research on suitability so know that they won't be perfect here's what I've got... Firstly, Castable - C1400, Secondly I have 60GD HS Cement. Can I use one or both of these castable and/or cement options to secure the bricks in the dome effectively?
(I am aware there is the conventional and heavily recommended 3-1-1-1 mortar mix which I could have opted for (and may yet have to!) although in the south of London I've not found a local place to buy fire-clay yet so hoping I can use what I have. )


Requests for clarity, and then any help, guidance or corrections-before-the-event all greatly appreciated and taken in the spirit intended! I'll set up a photo album to better tell the story of how I have arrived to this point very shortly.


Tim.

Hi...I want to talk about your "mortar" . the castable c1400 is not mortar and is castable refractory concrete that is used with forms to mold something like a dome shaped oven. The 60GD HS Cement Important and in my opinion is not what you want to use for your application because of the following spec that is attached to the product

* The Refractory cement will only set upon seeing approximately 300 degrees Celsius right through the joint. This kiln cement should be used between 2 to 5mm, any thicker and the cement may not set.

The joint can only be 2 to 5mm this is not a big joint.

Here are links to the information on these two products.

https://www.kilnlinings.co.uk/60GDHSCement
https://www.kilnlinings.co.uk/C1400

I would go with the homebrew mortar recipe which is 3:1:1:1 which is 3 parts mason sand and 1 part each of powdered fire clay, portland cement, and Lime. It will allow you to go with the bigger joints and is what most builders use.


Ricky

[Chach]

I would go with the Firebrick 42GD -230 x 114 x 64mm" its a standard size brick. I say ditch the plywood to fasten the IT to you do not need to do it that way. For your IT you can take the center floor brick out and temporary install a piece of wood in its place to fasten your IT to and use the plywood to protect the floor only when your building. Are you planning on enclosing the oven or keeping the dome shape? I would recommend downloading the plans from fornobravo and use this guide as a basis for your build. You are asking the right questions but make sure you use the correct products for your project.

Ricky

[Whackers]

I would go with the Firebrick 42GD -230 x 114 x 64mm" its a standard size brick. I say ditch the plywood to fasten the IT to you do not need to do it that way. For your IT you can take the center floor brick out and temporary install a piece of wood in its place to fasten your IT to and use the plywood to protect the floor only when your building. Are you planning on enclosing the oven or keeping the dome shape? I would recommend downloading the plans from fornobravo and use this guide as a basis for your build. You are asking the right questions but make sure you use the correct products for your project.

Ricky

Thanks, I've gone with the 64mm fire brick for the base and ordered the fire clay from ebay to avoid using the wrong products. I've removed the centre brick and secured a half brick slightly sunken and screwed the IT into it - I've laid the bricks out again this time on top of the Calcium SIlicate board.

The plan is to keep the dome shape, if I understand your question, so it should look like a pompeii oven, complete with the arches at the front incorporating the flue/chimney/landing area.

Here are some addiutional photos of where I am up to. The level is pretty good and I may get away with using only a very minimal layer of sand to 'bed' the firebricks on - is there any specific sand I should use?

Thanks again for responding, massively appreciated,

Tim.

[Whackers]

Hi...I want to talk about your "mortar" . the castable c1400 is not mortar and is castable refractory concrete that is used with forms to mold something like a dome shaped oven. The 60GD HS Cement Important and in my opinion is not what you want to use for your application because of the following spec that is attached to the product

* The Refractory cement will only set upon seeing approximately 300 degrees Celsius right through the joint. This kiln cement should be used between 2 to 5mm, any thicker and the cement may not set.

The joint can only be 2 to 5mm this is not a big joint.

Here are links to the information on these two products.

https://www.kilnlinings.co.uk/60GDHSCement
https://www.kilnlinings.co.uk/C1400

I would go with the homebrew mortar recipe which is 3:1:1:1 which is 3 parts mason sand and 1 part each of powdered fire clay, portland cement, and Lime. It will allow you to go with the bigger joints and is what most builders use.


Ricky

Thanks, yes will probably only use a small amount of the 60GD HS Cement to secure the first level of dome firebricks to the oven floor level as it will not need to be more than 5mm and will provide a solid basis for the rest of the dome. The rest of the dome I will be constructed with the home-brew you suggest, (as mentioned I've got the fire clay on it's way from ebay now and the rest I can easily get from the local builders merchants.) I'm not sure if I should use silica sand rather than builders/masons sand - which some advice suggests.

The castable....may be a lost sunk cost in this project entirely - lesson learned.


Tim.

[Whackers]

So, my current plan - please shout if anything is wrong/stupid/ill-thought through:

• Cut the floor bricks now they are all marked out for the dome and entry/floor front area.
• Cut the Calcium Silicate board to dimensions required under the fire brick floor.
• Lay the Calcium silicate on mosaic tiles and drill two or three hols through the concrete to enable any future damp to escape (use mesh to stop creatures from travelling in the opposite direction and making a home.)
• Cover the top of the Calcium Silicate with Aluminium Foil
• Lightly sprinkle sand on the aluminium covered calcium silicate board to enable fire brick floor to be laid level.
• Lay the floor fire bricks level on the above structure and ensure no raised edges or lips and no gaps between bricks.

That's the current plan, I'm going to work with an angle grinder and diamond blade for the cutting of the bricks, and see how I get on, it worked fine for cutting the half bricks, but will see whether it works ok for curves...if not I may need to go down the Mitre saw route, which I think I will need later in the dome build when it comes to shaping bricks to reduce the amount of home-brew fire clay mortar that I need - and improve the thermal qualities of the dome overall (a marginal considerations I think probably!)

[UtahBeehiver]

A couple comments, the pivot point of the IT is offset from the center of the dome. You may need to make some rod length adjustments as you go along, just something to be aware of.
Bullet 2 - If the dome is on the floor is okay if the the dome is outside the floor make sure CaSi is under dome.
Bullet 4 - Why the alum. foil? If for water issues, foil goes both ways, it will also keep in water that gets in.

Not sure what you mean by reducing the home brew and improve the thermal qualities.

[Whackers]

A couple comments, the pivot point of the IT is offset from the center of the dome. You may need to make some rod length adjustments as you go along, just something to be aware of.
Bullet 2 - If the dome is on the floor is okay if the the dome is outside the floor make sure CaSi is under dome.
Bullet 4 - Why the alum. foil? If for water issues, foil goes both ways, it will also keep in water that gets in.

Not sure what you mean by reducing the home brew and improve the thermal qualities.

Thanks, the IT was as good as I could do - will keep a close eye on the way it evolves though, thanks for the heads-up.

Bullet 2 - CaSi is under the floor and the dome will sit on the floor, so there should be no heat sinking possible. then the insulation blanket will come all the way down the dome later on to provide complete insulation all the way back to the CaSi.

Bullet 4 - yes it was to keep the water away - point taken - I think water/damp will likely approach from the perimeter if at all, so perhaps I could leave it entirely, or only employ it around the edges of the CaSi as an insurance policy. Could be overkill, but will buy me some peace of mind!

Reducing the amount of mortar required was what I meant, as I intend to shape the bricks (*not just use Half Bricks or square-cut bricks all the way up the dome) so I meant that they will sit closer to each other and therefore need less mortar to fill smaller gaps. Just badly described earlier!

[UtahBeehiver]

Mortar is your friend, I would not waste the time resource to cut the bricks to achieve a smaller joint. I did this and although it looks nice if I were to do this again I would only do a bevel near the top front interior to eliminate the Inverted V in the upper courses. Personally, I would skip the foil, raise the CaSi off the hearth surface with some cheap ceramic tile with spacing that leads to the weep holes..

[Chach]

Yes I agree not worth spending the time to make all the fancy cuts. The structure will be just as strong as it would otherwise and the thermal mass will not be compromised at all by using the homemade mortar.

Ricky

[Chach]

You also want to make sure you get that pivit point as close to the floor as possible. The center of the wheel should be the even with the floor line. You can use a piece of wood to secre it to which would make it lower than you have now. This will not fix what Russell said about your center point being offset due to the caster having an offset in it.

Ricky

[Baza]

Whackers enjoying both the pics of your progress and the honest questions you are asking as you go - helps others new to the process (like me!).
Both Utah and Chach have been great supports for me as well - they mentioned the same re: the cutting when I posited it ... and to be definitive - do you both advocate just straight 1/2 brick cuts with lots of mortar until the last few courses? Just 1/2 brick it up the dome?

[Chach]

Whackers enjoying both the pics of your progress and the honest questions you are asking as you go - helps others new to the process (like me!).
Both Utah and Chach have been great supports for me as well - they mentioned the same re: the cutting when I posited it ... and to be definitive - do you both advocate just straight 1/2 brick cuts with lots of mortar until the last few courses? Just 1/2 brick it up the dome?

I would..just 1/2 bricks and sometime 1/3 bricks as you get higher and just bevel the front edge as Russell said thats what I did and I was very happy with the way it came out.

Ricky