36" Pompeii in Indiana, US

[GreenViews]

Proud moment: Setting the dome keystone

Question: When should I insulate? Should I let it start curing and drying first or add insulation right away? I'll begin working on entrance and flue for now, thinking that insulation can wait a bit for better breath-ability as it cures, but I'm very interested in anyone's experience. FB guide v 2.0 seems to be silent on this question unless I missed it.

[UtahBeehiver]

Current school of thought is the dome is insulated but not the final coating, ie stucco, etc. The insulation helps temper the temperature differential between the inside of the oven and the outside,, thus reducing the potential of cracking. Caveat emptor, this stage of the build is where we really see a lot of excited builders hurry and fire too fast too quickly and damage/crack their ovens. Start with some charcoal briquettes that will get you around 200 F, then could a dutch oven while your at it. when you go to wood, one extra piece of wood can really spike the temp quickly. If you see any steam then you going too hot. The turtle wins the race here.

[Mongo]

Well done!
I thought I was the oddball in regards to the IT use. I never once used a clamp and placed my bricks 'by feel' as you said.
Exact art and subtle science.

I'm with Russell. There is no downside to a long and slow cure.

[GreenViews]

Planning entrance, flue, and finish:

1. Flue and entrance idea and dimensions: I'm considering the following: Flue area idea: full 9"x20" for 2-3" height, then at angle iron, abruptly narrow to 4"x 20", then smoothly taper (not shown) over 4 to 6" into 2- 4" clay flue liners (which I surround with colored p-crete for insulation) - see mock up in photos
2. Thermal break: I bought some insulating firebrick as thermal barrier, thiniking of cutting into 3 and 6" sections then building the 9" flue area up always with insulating brick against oven.
3. Entrance ledge down?: I'm considering keeping entrance ledge down 1/4" (with thermal break also) for ease of ash removal (by putting your scoop below ledge and pulling ashes onto it).
4. from arch to square with angle iron: for ease and stability and maximizing flue area, I'm thinking of using angle iron (brick not mortared to it and space for expansion/contraction of iron. My nice arch would still be quite visible from the entrance. I would the have my outer opening a little higher than by inner door, but lower than the rectangular flue area. This would allow me the option of making a rectangular door shape and even putting it on a hinge if I extend some angle iron down on at least one side. Hmmm.
5. I had an idea with a found item... I found a roll of woven fiberglass. Very flexible but strong, maybe used in boat building locally. I was considering wrapping the half soldier area of my dome with it, then making 6 distinct p-crete butresses up to top of my half soldier heights and behind the straight area of my inner arch. This way, with the buttresses just in spots and the thermal blanket covering the rest of the base of the oven, I get support behind my half soldiers all around, but maximize insulation by having most of it covered with fiber blanket. I see that glass fabrics retain 50% of room temp tensile strength at 700F and 25% at 900F. This stuff is strong at room temp, so I think that is sufficient! I honestly don't think I need support behind my half soldiers, but this would be a cautious approach without going too far overboard I think.
6. Materials and look: I found a buried piece of soft marble. Most likely going to shape that for the center outside of my entrance. Everything in entrance sits on p-crete on a sand/fireclay layer. I have brick that somewhat match my house, for the outside of my oven enclosure, but not enough for the whole thing and I find it kinda boring for the full surface area, but I have some river stone with fossils (shells and the like) in them that I got from my Father's house and I was thinking 2 matching panels of them on the front of the oven (surrounded by brick). I also found on my property some limestone and was considering making a mantle (after cleaning up), but the more I think about it, using some of the river stone as a mantle just might be even more unique and beautiful. Last photo shows some of the materials I'me looking at... Wondering if anyone particularly likes something. Not going to use all the different materials, but still deciding.

[BeanAnimal]

Don't care for the precut tile squares - too unnatural for something hand made. They grey brick go with the marble well.

[GreenViews]

Started entrance today. poured subfloor of entrance yesterday. I didn't want to wait to complete the flue area, so I put a couple firebricks in the p-crete under where the entance brick column. Most of this supporting brick was below the thermal mass area anyway and I kept it out with 3/4" p-crete between as well. In this build I used insulating fire brick cut to 3" and 6" alternately against oven with a cutout for my angle iron to later mount the door to. I also spaced so I can put thermal rope between the angle iron and oven. Tomorrow I plan to cut the angle iron and make extra large holes to join loosly with bolts to one of the chimney support angle irons... to allow for thermal expansion without causing stress on the brick.

[GreenViews]

Impatient entrance build: need to get the clock ticking on curing of flue area so I placed a couple firebrick on edge under where the walls will be and poured p-crete around these and between these and the dome. Any heat loss through this path will need to travel through 3/4" to 1" of p-crete over a 4 square inch area total and low in the sub-floor, so I think will be quite minimal. So today after setting up overnight I placed the entrance brick, tomorrow I'll prepare and set the angle iron (with room for expansion so doesn't stress the brick) and hopefully build up the flue. Oh I did set the entrance brick on top of sand/clay mix and used that for the small area where the insulating firebrick touches the inner arch. Did I do that right?

Thermal breaks: I added 2 which was just my best idea how to get the angle iron into the entrance for the door without turning it into a large heat sync. I have thermal rope which I will glue between the angle iron and the inner arch. On the other side of the angle iron, I have insulating fire brick (very light and insulates very well). Tonight I need to look up the thermal expansion properties of the angle iron to see how much slack I need to allow for movement.

[UtahBeehiver]

Suggest you seal off the fiber rope on the inside of the vent chamber with some high temp caulk, ie Kwool caulk, vcrete or equiv so the fiber that come off the rope do not contaminate the food area.

[BeanAnimal]

My wood burning insert has fiber rope - it is very soft and does not appear to be (at all) friable. I would be afraid that the caulk would prevent the rope from expanding an contracting to keep the gap sealed. Maybe just a thin coating of the super wool flexible caulk rubbed over the exposed leading edge to stay any loose fibers?

[GreenViews]

The fiber rope I have has stainless braid around it. I was going to tuck it way back in. Have people had problems with fibers getting into food? I tried looking for high temp flexible sealant other than rope and cannot find any available that takes up to 800 F and is food safe. I can keep an eye on it and leave it as an air gap if it starts fraying???

[GreenViews]

• Expansion calculation: found source stating over 1000 F rise in temp steel will expand 9 1/2" per 100 feet. I calculated from this I needed less than 1/8" expansion space vertically and 3/16" space horizontally, so I drilled out holes to bolt my 3 angle irons together that were 1/16" too large for the bolts and cut the uprights a bit too short, then verified I had in reality at least the expansion play needed before I tightened the bolts.
• Loose fitting angle iron around bricks: I cut notches for the bricks so the angle iron doesn't bind in any way.
• Thermal break: I had enough insulating firebrick for directly above each of the angle iron except for the ends of the flue for which I then used regular firebrick, notched for the angle iron.
• transition to 2 of 4" clay flue liners I had available. The transition will be over 2.5" widths of flat firebrick placed across the top of the insulating brick above the angle iron. Marked the top 4" circle, started to cut the taper and ran out of time for the day. My youngest graduated and I finished hooking up garden sprinkler system, so short day. Feeling happy about it.
• Bonus: we ordered take out from an expensive high temp pizza restaurant which is my daughter's fav place. Looking forward to being able to make equivalent (or better) pizza with her at home before she goes off to college in fall... and whenever she comes home.

[UtahBeehiver]

The ceramic rope is the same material as the ceramic blanket and PPE should be worn when working with these materials but once enclosed it should be good. So up to you on whether you seal the rope or not,, it just near the entry point of where food goes in and out. I used a HT caulk called Uni-Extreme(hard to find) that contained no hazardous materials, there is also Kaowool caulk but I am uncure on the MSDS on this one.

[BeanAnimal]

I looked up the kaowool caulk - it appears to have ceramic fiber in it. I did not check the MSDS, but assume it would be at least more encapsulated than the rope. FWIW - one of their caulks is listed as "hard" and the other "flexible". Whatever that means in terms of hardness.

[GreenViews]

Thanks for the info. I looked on ebay and amazon and cannot find the Uni-extreme product. I can locally get a (non-intumescent) fire blocker I have used in construction called White Lightning Flame Buster. Looking on it's MSDS, I'm not sure it would be safer than risk of exposure to the ceramic rope and I'm not sure if it is even flexible enough when cured or heated to be of use. I did find this link discussing the ceramic rope hazards (posted below). It focused more on workplace exposure and suggested a few increased disease risk areas. I'll wear protective equipment when installing! I'll also revisit my use of this product if I notice any rope fraying or disintegration at all. But I'm hoping In will be able to set it (with sodium silicate based cement) and forget it. I'll keep an eye on it now though. Gosh, now I'm wondering what people use for door seal. I was thinking of using some of the same. Thoughts?

[UtahBeehiver]

Don't know, I personally never used, but several builders have and not sure how flexible flexible is. The Uni Extreme I used set up hard though so placing on an highly expanding metal angle may or may not be an issue for Greenville.

As far as the door seal, mine is just a dry fit between the ss steel and the fire brick, is it a 100% seal, no but is does what I need it to do. More important is the have an "insulated" door. Carbon steel has a much higher K value than SS and thinner the gauge better.