Origen: 36" Pompeii Oven Build: Just getting started and have some questions....

[RandyJ]

Looks like you were busy today. I also see you came to the same conclusion that I did. It is just way easier to use the calsil than do the vermicreete. There is nothing wrong with it. Just a lot of work, and if you don't have the money it will do the job just fine. I think it cost me about $100 more to do 2 layers on my oven. I used 3 boxes for under the floor so $300. So for me it was worth the $100 to speed up the process.

I could be wrong but the dens glass that you are taking about I Think is like a exterior grade sheet rock. I don't think it would be suitable for what I think you are taking about. There have been a few people on the forum that have used it for there enclosure. That part is up to you. Cement board works great too.

Randy

[Gulf]

Origen,

Great form work. Vcrete has great compression strength, but very little tensil strength. The weight of your floor and dome brick will be easily supported by the vcrete. It takes about seven days for the portland in the mix to set. It will take about 28 days for it to cure. It will take much longer for it to dry. No matter how long you wait, the corners of the pour will chip very easily. While laying the flloor brick and building the dome, you will come into contact with those corners many times. Leaving the forms in place will protect those corners.

Gypsum products are great for heat sheilding and protecting flammable materials like wooden framing. However, they do that by absorbing heat. Eventually, the gypsum will be heat saturated, and the heat will eventually spread to what ever it is touching. I think that I remember that two 5/8ths thickness of sheet rock ( on each side of wall) gave about 30 minutes of burn time for a fire to spread from one apartment to another. If it is absorbing heat, it is also robbing heat from where you want it to stay. You want as much heat as possible to stay in the oven.

[Origen]

Thanks very much for the information. Do you know if vermiculite concrete can take a screw? Either concrete or wood? I think I am going to have to move the forms: I don't think I can get a proper visual with them in place. That's just me. I was thinking of wet forming a 3/8" strip of plywood the height of the vermcrete and screwing it into the vermicrete; you know, to give the perimeter integrity during the build.

[Gulf]

My vcrete held 3" deck screws fairly well. I used the deck srews to fasten my chicken wire at the bottom. They were into the floor vcrete about 2". It was several months between pouring the floor insulation and installing the wire over the dome insulation. I'm not sure that the screws would have held within a week or two of the pour.

I removed my forms before I placed the CalSil. I rembember regretting it, but I was able to stay off of the dome floor insulation fairly well. For me, the area that took the most abuse was the entry floor insulation. You should be ok to remove most of your form after a week imo. However, I don't see where the entry form would be in your way until after the dome is built. If it is, I've seen some apply their excess mortar on those edges.

[Toomulla]

Origen,

Great form work. Vcrete has great compression strength, but very little tensil strength. The weight of your floor and dome brick will be easily supported by the vcrete. It takes about seven days for the portland in the mix to set. It will take about 28 days for it to cure. It will take much longer for it to dry. No matter how long you wait, the corners of the pour will chip very easily. While laying the flloor brick and building the dome, you will come into contact with those corners many times. Leaving the forms in place will protect those corners.

Gypsum products are great for heat sheilding and protecting flammable materials like wooden framing. However, they do that by absorbing heat. Eventually, the gypsum will be heat saturated, and the heat will eventually spread to what ever it is touching. I think that I remember that two 5/8ths thickness of sheet rock ( on each side of wall) gave about 30 minutes of burn time for a fire to spread from one apartment to another. If it is absorbing heat, it is also robbing heat from where you want it to stay. You want as much heat as possible to stay in the oven.

Gypsum board resists fire by evaporating the moisture in the gypsum, boiling off the water uses the energy of the fire thus making the board fire resistant it only works once. I.e no moisture left no insulating value

[RandyJ]

I removed my forms before I placed the CalSil. I rembember regretting it, but I was able to stay off of the dome floor insulation fairly well. For me, the area that took the most abuse was the entry floor insulation. You should be ok to remove most of your form after a week imo. However, I don't see where the entry form would be in your way until after the dome is built. If it is, I've seen some apply their excess mortar on those edges.[/QUOTE] I smeared all my excess mortar on my oven as a cladding you could just start at the bottom and work your way up as you go. Just a idea. Randy

[Origen]

Thanks very much for the feedback regarding the vermiculite concrete--very helpful. I was also wondering if chicken wire/lathe could be screwed to it, so that is good to know. I think I will keep the form on the landing, and I have a couple of ideas to protect the dome perimeter.

Thanks also for the gypsum feedback: that hair-brained idea was filed away--it was born of self-irritation caused by making a poor decision!


While I'm waiting for the vermicrete to evacuate moisture, I will cut the floor/landing and try to figure out the arch. I certainly will have some questions. I did find a photo with notations here that went a long way to helping me get that concept; I will post that photo soon.

I had a question about the chimney: I'm planning on using clay flue pipe, and due to adjacent structures, I'm thinking that chimney will be maybe six feet off the top of the arch. I think a 6" round flue is correct for a 36" oven. That's OK, right? I'm a little bit familiar with fireplace design and draw, but these aren't fireplaces. I would think if the flue chamber (above the arch) has good volume, a 6' chimney would draw fine. But...I would like to know from someone who knows!

[Gulf]

6" is ok for a 36" or smaller pompeii. That is sort of at the border line. But, with 6' of height that should be fine. Though, one draw back to that is the weight that you should consider when building your outer arch.

[Origen]

Thanks, if I increase the chimney to 8" will that improve performance? At this point, I have no problem upsizing. If 6" is borderline, that concerns me. With most things, you want to be in the middle range not the edges, right? If (and this is a big "if", especially for a rank amateur arch builder) the arch is constructed properly, it should be able to hold an enormous weight, shouldn't it? Think Colosseum. I don't think my shrinker/stretcher can bend 1/4" angle iron, so I can't sneak structural steel in there! I will also consider a stainless chimney, but I do like the aesthetics of clay.

Rain and moist vermicrete are seriously depressing me...and any progress.

[RandyJ]

I would think that the 8" chimney will help it breath better so you will get less smoke staining on the entry. Also you are right if you build the arch right it will hold a lot of weight.

One question I was just wondering where in the world you are at?

Randy

[Origen]

My vermiculite concrete took a long time to dry! What a waste of time! It took so long that to quell my impatience I moved indoors and painted a few rooms. We did have a ton of rain for numerous days, so maybe it was the humidity--I had it double-tarped, so I don't think it got wet. I attached some pictures of the vermicrete--I don't know if you can tell from the photos how moist it was. I left it exposed to air and partial sun for 3 days after the tarps were removed, and it still seemed wet. I pulled the forms to give it as much exposure to drying air as possible. I made a "test brick" of vermicrete to put through the paces: test strength, screw holding power, heat and moisture resistance, etc.).

I ran into a bit of a problem. I cut my CalSil and placed it on the vermicrete. It "rocked" a bit, and in the interest of it being dead level for the bricks of the floor, I figured I would use the fireclay, sand, water mixture. I mixed that blend and tried applying it with a 1/4" trowel. The plan was to bed the CalSil in the fireclay sand "mortar". I don't know if the fireclay makes that setup quick or what, but I couldn't get that to trowel well at all. So, what should I do: screed over the vermicrete with some portland/sand mix to get dead level and then just float the CalSil on that once it dries? I do like the idea of the CalSil being somehow adhered. I know it's not necessary, but what's the best route to do that. I also like the idea of the oven floor (the bricks) somewhat adhered as well--not an unbreakable bond, but something to prevent them shifting. What's the trick for mixing sand and fireclay to get it trowelable. Also, I assume the sand fireclay can be re-tempered since there is no portland in the mix--that is, I can re-use that, right? I have the CalSil and floor bricks cut, and I'm really anxious to get going.

While I was waiting for things to dry, I was debating if I should use homebrew mortar or HeatStop (or comparable). It sounds like homebrew is less likely to crack, so that is the route I'm going. I have dry mixed two 5g buckets ready to go! I am curious though: why would the premix be more likely to crack? They are both basically made from the same raw material--right? I would really like to know the reason for this.

[Origen]

Today...I plug the Dome and depart the NIne Circles of the Inferno (quite literally as courses 4-12 inclusive challenged me greatly). On to Purgatorio...





I did try to post photos, but I was persistently rejected!

[UtahBeehiver]

There is a limit of 5 photos per post and size of each photo limited.to I believe just of a meg.

[Origen]

Strange...the last post I made with photos was effortless. So were all the other posts I made with photos! I was going to post 3 photos. I just tried again and again received an error message (Image thumbnail creation failed from JPEG). This oven was not destined for glory! Either way, I'm going to finish the vent and then post some advice (based on my experience) for those contemplating a build.

[Origen]

This was a very good feeling...