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

[Yeager]

The 2.5" thick insulating bricks I got were rated at about 1/2 to 1/3 of the ceramic fireboard I was using, so its not as good as a calsil, but a good combo to it. I think each brick was only a couple of bucks also. They are very light and easy to cut also.

[Origen]

Thanks for all the input. You know Yeager, I was actually thinking about using insulating bricks while I was building the form, and exactly for the reason you mentioned: saving time and getting to the build! I think I am going to be faced with rain tomorrow, so it may give me a little more time to contemplate. I have to imagine insulating bricks are on par with CalSil (and I mean refractory insulating bricks, not the bricks used on the dome). Regarding CalSil: aren't calcium and silica (and alumina for that matter) some of the most abundant elements in existence? You know where I'm going with this...what's with the cost. I'm certainly no chemist, and I have no idea what goes into the process of manufacturing, but it's hard for me to grasp!

JR, I actually have a template for the hemispherical arch (I kind of like to say the word) and I was initially planning on using it. As I have gone through, and continue to go through build threads, I don't see too many of those. I was actually drawing a flattened arch template yesterday, but I didn't cut it as I decided I better focus on the insulation. Which arch is easier to tie into the dome? Intuitively, I would think the hemispherical; but, this is the first masonry sphere (or more accurately, half sphere) that I have ever attempted to construct, so I do not know. I assume this is strictly a build issue: I can't see how performance would be affected by the style of entry arch. Please correct me if I'm wrong.

[Yeager]

Another idea for you that may be simpler is put a layer of insulating brick under your calsil. It will have almost the same insulating properties as your vermiculite and is more tolerable of moisture (and elevates your calsil off the floor to avoid moisture wicking in). That's how I built my oven - 2.5" of insulating brick and 2" of Ceramic Fiber Board. The simulators show it dropping the temperature from a 800 degree oven floor to around 160 degrees under the insulated brick. The bonus is less work and you can continue building right away with the insulating brick vs vermiculite.

-Yeager!

[JRPizza]

I meant to ask - are you going with the flattened arch shown in the picture you posted above, or a hemispherical arch like this one.

[JRPizza]

Vermiculite can soak up and hold quite a bit of water, so you have to put as much water in the mix as would normally be required for the amount of portland you added, plus the amount of water the volume of vermiculite you added wants to absorb. After the reaction is done (the vermicrete has set), you have to give the water absorbed into the vermiculite structure time to exit. If you cover it with the CalSil too soon, it will take much longer for the vermicrete to dry.
Interestingly enough, looking at Wikipedia I see that vermiculite is used in the manufacture of CalSil board:
"Calcium silicate boards: exfoliated vermiculite is added to a calcium silicate slurry, this is then dewatered by pressing or by using one of the Fourdriner/Magnani/Hatschek processes to form a flat board which is then heat cured under pressure (typically 10-15 bar) for periods up to 24 hours."

[RandyJ]

I think it has to do with there being more water in it to help bind everything together. So it has to dry out some first. Not all if it is used up in the chemical reaction with the cement. I hope this helps or if I am someone who knows will chime in. Good luck getting started. If you have some serious time to put in to the build you can make quite a bit of progress. Good luck

Randy

[Origen]

After honoring all the Mothers I know, I decided to pour 4" of vermicrete and put 2" of CalSil on top of that. I just built a form and photo'd it. If it doesn't rain tomorrow, I think I will mix and pour that. So Vermicrete takes a week to dry? That seems unusually long--can you explain that to me? It's not that big a deal, that delay-I can cut the floor bricks and make an arch template and start contemplating the arch I suppose. I have a window over the next 4 or 5 weeks where I will have more time to work on this than would normally be available, so I have to hit it hard. After that, it will be very sporadic!

[david s]

How about a compromise and lay a 1" vermicrete slab with 2" cal sil sitting on top of it. The cal sil will provide a nicer flat surface to lay your floor on to. Give the vermicrete a week to dry out before placing the cal sil on top of it though.

"
One question I would like clarified: for a 36" oven, a 19" opening at around 12" in height would be fine, right? Also, the vent landing: 14" (dome opening to the front of the oven) is that OK? I have seen some info that suggests that a larger landing area might be more desirable."
Not quite sure I understand this question correctly. The inner oven door should have a height approx 65% of internal oven height. Make the width whatever you want, but the wider it is the easier the oven will be to work, but the greater the heat loss will be.The outer decorative arch needs to be both wider and taller so an oven door will fit against the rebate of the inner oven mouth.

[Origen]

I'm debating between pouring 4" of vermiculite concrete or grabbing more 2" CalSil; CalSil is painfully expensive! I also don't want to be stupid cheap so I have not decided what to do. I want the oven to be an engineering marvel--like you guys! I want it holding heat for a loooong time.

Why is a slip sheet recommended between the CalSil and the hearth? I can somewhat understand having an airspace--that would add insulation value in the right circumstance. So what would be used to shim the CalSil off the hearth?

I want to do a brick arch, but I'm not sure it's within the realm of my ability. I know how important this part of the oven is, so I certainly don't want to bollocks it. I started looking at the dome calculator and I started dusting off the part of my brain that learned geometry so many years ago, and I have looked at hundreds of outstanding forum photos...I think I need to get the insulation worked out and get the floor down so I can get my head wrapped around the dome and arch. Unfortunately, I was not blessed with excellent spatial imagination--I have noticed many builders here have that skill--it is a great gift. I am having a little trouble getting started: I know how I am--I don't fully understand this so it's paralyzing me a little!

One question I would like clarified: for a 36" oven, a 19" opening at around 12" in height would be fine, right? Also, the vent landing: 14" (dome opening to the front of the oven) is that OK? I have seen some info that suggests that a larger landing area might be more desirable.

[gastagg]

Origen, I've got 2" of CalSil and have no problem getting up to and holding heat, and after I saw the tech specs, 14 degrees is nothing, especially when you're at 550-700 degree floor temps. If it's going to cause delay and cost a lot more, I wouldn't worry about it. Once you get moisture out of the build, you'll be set.

[JRPizza]

I went with 5 inches - would have been happy with 4, but two cases of 2.5" gave me two layers of board with very little left over. I didn't want to mess with perlcrete, but you can always supplement your board with a layer of insulating concrete - I think many of the builds, especially some of the older ones, were done that way.
Have you decided on what kind of an arch you are going to build yet? If you have not done it yet, you can use your IT (or a cad program) to make sure you have the fore-aft placement of your inner arch in the correct location. It's a good thing to do before you start mortaring.

[RandyJ]

I think that the calsil board is twice as efficient so 2" is at least as good as 4"of vermicreete. . Don't break the bank but you do want to do what you can afford. .

Randy

[Origen]

Actually, I just thought I should test my newly learned photo uploading skills on uploading the original photos! A little slow on the draw there...Anyway, here are the originally incorrectly-posted photos.

[Origen]

Thanks JR. When I previewed the post, I couldn't figure out how to enter the photos properly. Thanks also gastagg; I will check out the dome calculator. I have to think about the insulation--if I want to add more to the floor. It would be a bit of a delay to get more calcium sil., but I might bite the bullet. Vermicrete is not as good right? Do you know how much vermiculite concrete equals 2" of CalSil board? I'm actually going to add a photo to this post to test my newfound photo loading skills! The photo was taken off one of the forums: it's how I want my dome to look!

[JRPizza]

Origen, when you attach pictures, if you use the camera icon in the upper left of the reply box the photo's will show up as thumbnails and make it easier to review your build. I think you probably used the file icon in the upper right, which is what you want to use to upload PDF's, cad files, etc.