28" Oven in Seattle

[JBA]

Since the oven was functionally finished in late July, it has been fired up about a dozen times when the weather has been dry. Apart from cooking the mandatory pizzas, I've also tried my hand at pita bread, ratatouille, fish, roasting various vegetables and chicken, and even things like lentil soup using retained heat. Speaking of retained heat... the generous insulation and extra floor thickness really holds in the heat for a long period of time!

It's been exciting to cook various foods in the oven and understanding the dynamics of it. Hopefully the oven does well sitting under a tarp through the wet season in Seattle. Next spring I plan on adding the remaining cosmetic touches such as pouring a concrete countertop around the oven, rendering the dome and stand, and adding a few coats of paint.

Here's a few pictures of foods cooked in the oven:

[david s]

Curing/Drying cracks after the final fire that cleared the dome:



None of the cracks exceeded 2mm.
They occurred at the very top, around the gallery, and at the back of the dome.

Apart from raising the temperature too fast, cracks are more likely if the drying fires are done with the the oven uninsulated. This is because there is a much greater difference between the inside and outside temperature of the bricks. This leads to uneven thermal expansion and a greater propensity for cracks to develop. If the dome is insulated the temperature is much more even. Nothing you can do now, but maybe keep this in mind for the next oven you build.

[MarkJerling]

Looking good. And you even got in the newspaper with it! Well done!

[JBA]

Oven door. Built using sheet metal and stainless steel rivets. Temporary for now until I can have someone build something nicer for me.

[JBA]

Insulation: 3" of ceramic fiber blanket, and about 1.5" of vermicrete.





I also got a feature in the Seattle Times!

[JBA]

Curing/Drying cracks after the final fire that cleared the dome:




Also note the use of an anchor plate attached with tapcon screws, sealed with high temp silicone. Double wall 3ft and 6in diameter chimney attached to anchor plate.





None of the cracks exceeded 2mm.
They occurred at the very top, around the gallery, and at the back of the dome.

[JBA]

Wide angle shot from the inside (after drying).



The top doesn't look great as mentioned in previous post.
I also didn't mortar and tuck the gaps smooth between the bricks on the inside. I don't imagine it makes much of a difference to the performance of the oven, but I'll take any advice on it into account for a future build.

[JBA]

Next up: Brickwork.

Building the dome tier by tier. I mixed a homebrew refractory mortar. Lots of wedges between the bricks. Flue gallery and chimney base with carefully angled cuts.

For the last tier and capstone impatience got the better of me and the fit and finish on the inside suffered a bit. Still very much functional though.

The build videos on the YouTube channel 'Artisan Made' really helped me.

[JBA]

It's been a while since I last posted on the progress of my oven build. While the oven is nearly finished and has already been used to cook pizza, I will dedicate the next few posts to documenting the build process, hoping that it might help someone in the future.

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After the hearth was poured, I drilled several holes in it and laid out ceramic tiles to elevate the 4" calcium silicate board. In hindsight, I've learned that I should have laid the ceramic tiles bottom facing up, but it should still be better than nothing.

The calsil board was cut to shape with a jigsaw and covered with aluminum foil to protect from moisture.

The firebrick was laid on a thin bed of fire clay and sand mixture. I think I was able to get the floor pretty even. Note that I placed the floor brick on their side for extra heat retention. The floor thickness is 4.5 inches.

For cutting the bricks, I used a 10" sliding composite saw from Harbor Freight that I fitted with a diamond blade. Bricks were always soaked before cutting but there was still an incredible amount of dust. A mask was a must-have.

[david s]

If cost is a major issue the use of either perlite or vermiculite mixed with portland cement to create what we call vermicrete, is an alternative. The underfloor mix should not be leaner than a 5:1 mix and the over the dome mix should be around 10:1. There drawback is that because water is added to the mix it requires considerable drying after it has been placed before building over it. See the attached table for strengths and insulation values for different strength mixes.

Note: The thermal insulation value is a function of bulk density and particle size; generally the lighter the mix the greater the thermal insulation will be. When the same volume of different grades of exfoliated vermiculite are incorporated into a standard mix, the final density (and therefore, the thermal insulation) will be influenced by the fact that the finer grade of the vermiculite used the denser the product will be. Conversely, a mix based on coarse and mid-sized exfoliated vermiculite will generally have the same thermal insulation value at ambient temperatures, but, at elevated temperatures the finer particle size aggregate concrete will be more insulating due to a lower thermal diffusion.

For vermicrete mixes I use a 50/50 (by volume) mix mixture of fine vermiculite and medium perlite for the above reason. It also makes up a more workable mix to apply, particularly useful in the leaner mix proportions.

[JBA]

I've never heard of them but I bet if you ask them for densities and compressive strength data they could probably send you some. I'm attaching the spec sheets for the board and blanket I used just to give you something to compare to if they do send you some data. I've seen recommended minimums for both here on the forum (I think from Russell or Joe) but can't remember what they are.
Did you check with the folks in Kent I had recommended in an earlier post?
Just noticed the Simond folks are showing free shipping! That could really be a deal maker depending on specs.

Thanks for the spec sheets! I will make sure that the ones I found are up to par before I order.

Unfortunately it looks like the store/business in Kent is no longer there. There used to be a Harbison-Walker in Kent from what I've gathered but the closest one now is near Portland. A little too far for me. I may search for other local businesses in Seattle that carry ceramic fiber board, but the options I've seen so far are very expensive and probably of much higher spec than what I need.

[JRPizza]

I've never heard of them but I bet if you ask them for densities and compressive strength data they could probably send you some. I'm attaching the spec sheets for the board and blanket I used just to give you something to compare to if they do send you some data. I've seen recommended minimums for both here on the forum (I think from Russell or Joe) but can't remember what they are.
Did you check with the folks in Kent I had recommended in an earlier post?
Just noticed the Simond folks are showing free shipping! That could really be a deal maker depending on specs.

[fox]

No I dont have any experience but it looks and sounds just like any other ceramic board however they do not quote the Density, the one that I use is 300kg/m³.
On a side note it seems to me that ceramic fibre is very expensive in America, I pay about half of that in the UK so I dont know if the one you have linked is good value?

[JBA]

Does anyone in here have experience with ceramic fiber board from Simond Store?

I'm looking at this

It's much cheaper than other alternatives that I've found online and locally, but it really makes me wonder if the quality is up to par.

[JBA]

Thank you all for the helpful replies!

JRPizza: I called Mutual Materials and they had fireclay! Thanks for the tip.

Latest progress includes the hearth being finished. Came out pretty good I think considering this is the first project I've worked on that includes pouring concrete. Next up I will revisit my oven design with a few minor updates and prep for building the dome starting second half of June I hope.