Looking for affirmation!

[lventi]

Thank you in advance! I've been attempting to follow the DIY Tuscan plan; so far, we have foundation, concrete blocks, cement hearth with major rebar, 4" of vermiculite/Portland mix. Our plan is to mix the sand/fireclay/water paste then lay fire bricks on the entire hearth (overkill but we like the look). Then we'd mark the bricks for an ~40" interior diameter, put some newspaper down, then build a sand dome so the middle is 21" high. The dome-building should be a real challenge, but hopefully the sand will help. Anyway - firebricks and high heat mortar...I guess we'd keep building up and eventually in theory make the bricks smaller and angled, ending with a keystone piece and mortaring all in place. It sounds like it doesn't have to be beautiful, since it will all be coated in mortar plus vermicrete. (How thick should the outside mortar be?) We'd add a regular (not fire) brick vent 20" wide and 12/5" high with a 1-2' chimney, near the oven door, also made of regular brick. (Does the chimney need to be lined with anything or just regular brick?) On the outside of the dome (not the vent, right?) we'd apply 6" of vermicrete (is this correct? I've also read that 4" is enough). On top of that would be the wire stucco lathe, rough stucco, then waterproof stucco. My impression is that we do not need vermicrete on the vent - is this correct? Then we think we'd be ready to start curing...200 degrees, 300 degrees, etc. (Do we need to let it sit or keep it moist at all or is it ok to just start lighting fires as long as we start low? Somehow we'd make a door, also, and a chimney cap. Wow - it's a little overwhelming.

I'd love confirmation or rejection!! Thank you for your help,
Another Struggling Portlander

[JRPizza]

Have you considered building an IT in lieu of using the sand dome? Using one makes it relatively easy to keep the dome bricks in proper orientation and allows cleaning and inspecting the inside of the dome as you build. Some of the ovens I have seen built using internal structure (sand/balls) seem to not be as tight/clean as ovens built using an IT.
I'd also suggest doing a little reading of other builds (if you have not already). Below I have two links - the first is a collection of links to good oven builds, the second to a topic about what builders would do differently a second time. Both are good reads!


https://community.fornobravo.com/for...n-the-archives

https://community.fornobravo.com/for...change?t=12453

[lventi]

I read about the ITs...I was a little intimidated by the sound of it but will take another, more in-depth look! The sand IS worrying me a bit. Thank you so much - I'll read the 2 links!
ASP

[mongota]

The use of an IT does simplify things.

Some of the ITs that have been built have been on the intricate side. Simple works as well. For a first timer building a dome, the most basic of ITs will give you a better dome than most any other technique, especially where the dome starts to intersect and cover the dome arch. You don't have to think. You just mortar it up and place the brick, The IT does all the thinking for you, it'll keep your layout true.

Also, heed what JR wrote regarding being able to inspect, clean, detail the mortar joints on the inside of the dome as you go. Doing it as you go is so much faster and easier than trying to do it afterwards.

I just found my IT a couple of days ago. My build is next to my pool pergola. I stood on my hearth slab while building my dome, when I removed the IT I just reached over and placed it on the roof of the pool pergola. And there is sat for the past year or so!

[lventi]

Oh my gosh I just started reading about your build...crazy! A little depressing really, for those of us who are TRUE newbies in every sense of the word when related to building. You're a true artist and clearly a builder. We're simply hoping that this thing stands in the end and fires up hot - forget the beauty. I'm mostly concerned about the foundation b/c there's no rebar in it, but it's too late to do anything about that. Our thinnest side is on hard clay/ground and is 4", then gets thicker as the ground is a little sloped. My other concern is the building of the dome! Since I have you "on the line," do you mind checking this over? Our current plan (changes every day) is to use a makeshift IT - basically just a 20-21" stick or dowel or something that we can put in the middle of our dome to check for distance all the way up. We were going to mock-lay the dome to approximate shim or amount of mortar needed to angle up the outsides of the bricks to form the dome. Then I thought we'd use some chipped fire brick as the outside "shim" - any issue with this? Or maybe find some glass that can get to at least 1200 degrees.
Our plan is to make the sand mix to put on our 4" of vermicrete floor, then set the fire bricks in a herringbone pattern (well, and some other tricky pattern for the vent). Then we'll set 1/2-bricks upright directly on the brick floor (no mortar, rt?). Then we'll start laying 1/2 bricks on their sides, fat side down, directly on the upright layer...no high heat mortar on the inside where the bricks touch, only on the outside that's being held up by our makeshift brick shim. Then we'll mortar around the brick shim and keep at the right distance from the center by measuring with our makeshift IT stick. not sure how this will work when we get 2/3 of the way up, but we'll find something (ie a person) to go inside and hold up the pieces until they set maybe. Once the keystone is in, they're supposed to stay put in theory...right? How quickly does the mortar set? If our shims are a little off that's ok - function over beauty in our case. We figured we'd wing a vent of regular brick and mortar with an 8-9" pipe as the chimney. Lots of builders are saying that they wish they had a larger vent...they're talking about the tunnel as the vent right? Are they meaning a longer tunnel or a larger opening to the oven? I'm assuming a larger opening to the oven. For my ~42" interior, I'm planning 21" high with vent opening to oven of 13 1/2" and width of 20". (I think that's where the plan says to go with 12.5" high but the magical percentage seems to be about 62-66% of the 21" height?) Final question for now: do I put mortar down on the oven floor but under the first course of dome, or do they just sit on the bricks and are mortared between them only? Follow up to my last and related question: do I mortar between courses, or the mortar only goes between the bricks per course? Thanks a zillion,
ASP

[lventi]

Uh oh I have more:
Do I put any Heatstop on the outside of the dome once built, or just use it between the lifted part of the bricks? Can I put the 6" of vermicrete on the dome as soon as the dome is built (ie no curing)? And then I can put on the wire stucco lathe, rough stucco, and waterproof finishing stucco as soon as the vermicrete is primarily dry? Ie all of this in a day if it's possible so we can start the low heat fire/curing process or is it supposed to sit between steps?

[lventi]

And if I AM supposed to put mortar between layers of bricks, how much?

[UtahBeehiver]

A IT, stick, string, etc accomplishes two things, first, consistent diameter of the oven. second, the correct tilt of the brick so it is perpendicular to the center point of the oven.

[lventi]

Ah makes sense - pretty darn logical. Thank you -

[JRPizza]

Iventi, take a look at my build - my oven was the first masonry project I ever attempted other than laying some wall blocks in the yard to make a garden. If you can get a functioning IT built your concerns about shimming and filling gaps will kind of take of themselves. You would lay your first ring of bricks flat, then as you build the dome the IT allows you to work without shims. You can just "butter" the underside of the brick with mortar, then position it in place with the IT and push it down to squeeze out the excess mortar. Clean up what extrudes out and move on to the next brick. I would end up with gaps on the sides of the brick that I just troweled mortar into. My build is very far from the most artistic but I tried to get in enough pictures to show what the process was.

[lventi]

Whew - exactly what I was looking for - thank you!

[david s]

Uh oh I have more:
Do I put any Heatstop on the outside of the dome once built, or just use it between the lifted part of the bricks? Can I put the 6" of vermicrete on the dome as soon as the dome is built (ie no curing)? And then I can put on the wire stucco lathe, rough stucco, and waterproof finishing stucco as soon as the vermicrete is primarily dry? Ie all of this in a day if it's possible so we can start the low heat fire/curing process or is it supposed to sit between steps?

I’ve not used Heatstop but it is recommended for thin mortar joints only. It may be better to fill the larger gaps on the outside with homebrew. Some brick chip off cuts can also be used to fill them as well as the mortar.
Regarding your vermicrete over the wet dome issue, it would be a better idea to allow sun and wind dry the dome, weather permitting, before adding a vermicrete layer over it. The reason is that wet vermicrete directly over the dome, particularly if there’s no blanket layer separating them, can remain wet long after it appears to be dry. Once fire is applied to the interior dome the water in the vermicrete layer can make it swell and crack. To avoid this it is best to add the vermicrete in layers of around 35 mm with a weeks drying in between. A cheap garden moisture meter can be used to monitor the moisture level deep in the vermicrete layer during the curing fires. It is better to drive out the water before rendering the outer shell. You can hurry things along, but risk damage, but going slow is safer. You can always use the heat from the drying fires to do some roasting and baking. There’s no better way to roast chickens. Hope this makes sense and is useful to you.

[mongota]

"Our current plan (changes every day) is to use a makeshift IT - basically just a 20-21" stick or dowel or something that we can put in the middle of our dome to check for distance all the way up. "
You can do that. Just do your best to maintain the proper inward tilt of the brick so the inside face of the brick is perpendicular to your IT. That way the inside of the dome will have a relatively smooth face...the top and bottom edges of each brick will align with the course of brick above and below it for a smooth surface on the dome.

"We were going to mock-lay the dome to approximate shim or amount of mortar needed to angle up the outsides of the bricks to form the dome. Then I thought we'd use some chipped fire brick as the outside "shim" - any issue with this? "
Excellent plan. Uses up your cutoffs and saves on mortar. See me previous answer. Shim them so the inside face of the brick is perpendicular to a line coming from the center of your dome floor (essentially, your IT.

"Our plan is to make the sand mix to put on our 4" of vermicrete floor, then set the fire bricks in a herringbone pattern (well, and some other tricky pattern for the vent). Then we'll set 1/2-bricks upright directly on the brick floor (no mortar, rt?). Then we'll start laying 1/2 bricks on their sides, fat side down, directly on the upright layer...no high heat mortar on the inside where the bricks touch, only on the outside that's being held up by our makeshift brick shim. Then we'll mortar around the brick shim and keep at the right distance from the center by measuring with our makeshift IT stick. "
I'd recommend using some mortar when you set your bricks, even if it's just to seal the inside face edges to one another. If you simply dry set them with shims and come back later try to force mortar into the joint from the outside, it might be tough to get the joint full. It would also be easy to accidentally displace a brick since they are loose set. I'd at a minimum shmear the inside half of the brick with mortar, hopefully mortaring the brick shim on place while at it. That'll prevent the shim from moving from an accidental nudge.

"not sure how this will work when we get 2/3 of the way up, but we'll find something (ie a person) to go inside and hold up the pieces until they set maybe."
Use sticks. I had very thin pieces of stick that were somewhat flexible. They're not really carrying any weight. They're just preventing movement.

"How quickly does the mortar set?"
Mix small batches. I also soaked my bricks in a bucket of water, then a few minutes before I was going to set them, I'd pull them out of the water and set them aside. By the time I set them, the bricks were moist enough so they didn't suck the moisture out of the mortar, but not so wet that they slid off of one another. You'll develop a feel. And a sense of timing. The mortar sets or stiffens up pretty quickly, well enough to hold it's place on the dome. But you could still pop it off if you wanted to. It'll be set up hard the next day.

If our shims are a little off that's ok - function over beauty in our case.
Not to belittle that remark, but do try to build well, try to build accurately. Even with the best of intentions your bricks may wander off here and there. But errors due to apathy in your first few courses of brick will be magnified as your dome builds upward. This was my first build. I'm not a builder by trade, but I do a lot of DIY stuff. I do make mistakes, some can slide, some need to be remedied. You'll develop a feel for cosmetic errors versus structural ones.

We figured we'd wing a vent of regular brick and mortar with an 8-9" pipe as the chimney.
I have an 8" round chimney pipe. A standard size. So I made my vent 8" square, that way it could accept the 8" round protrusion on the bottom of my chimney anchor plate. My 42" oven draws well with the 8" pipe. I radiused the bottom edges of the brick that make up the 8" square vent opening, I hoped that would give a smoother, more laminar flow to encourage the smoke up the vents versus come out out the face of the vent arch. Can't say that it helps, but the chimney does draw well. So I have a 64sqin vent feeding a 50insq chimney pipe. Again, it works well in my build.

Gotta run...hope this helps. And...it's all my opinion. Listen to the smarter guys if they reply.

[mongota]

Here's a pic of the support sticks I used. Maybe 3/16" square. I ripped them from a piece of scrap lumber.

[shanxk8]

Hi Iventi,
I'll chime in as i did use heatstop (heatstop 50 dry; not the premixed stuff) to construct my oven dome. The post linked below from my build thread is the point where i started making really good with my dome. I tried to keep my mortar joints tight, but was less successful than I'd hoped for. The gaps probably got up to 1/4" at the outside edge of the vertical joints and was closer to 1/2" for the outside edge of the horizontal joints between each brick course (pictures in thread should explain better). I did not use any brick wedges to fill the joint gaps and the dome turned out fine (so far; curing fires +4 or 5 cooking fires). After it was cured i'd even stood on the dome and it is still standing.

I didn't do a final exterior coat of the entire dome, but did fill the outside joint gaps with homebrew mortar to bring them mostly even with the outside face of each brick. (I used homebrew mortar on my vent arch as i did not have enough heatstop and didn't figure it made sense to buy another expensive bag that I would not use even one half.)

https://community.fornobravo.com/for...049#post405049