36'' brick oven in northern Sweden

[johanr]

Hi!
I have started a pompeii brick oven project and thought I would start my own thread to show the progress and ask some questions underway. The planned oven is a 36'' (91 cm) internal diameter on a block stand (150x190 cm) laying on a concrete slab (170x210 cm). Yesterday I poured a 4'' vermiculite-concrete insulation layer on top of 3.5'' structural concrete layer. The vermicrete seems to set so in a few days I guess I can start laying the floor. I am planning to use home brew mortar according to recipe on the site but the only fire clay I have been able to locate is reinforced with iron filings. The lime I can buy is non-hydraulic slaked lime that I guess should be fine.
1. If anyone has some idea whether I can use the fire clay with iron filings or if I should look further, I would be grateful for the advice. I have also located standard clay (intended for tile oven), although not specified as fire clay, and I am not sure of the difference.
2. Should vermicrete be water-cured for 3-5 days as normal concrete would?

I'll post some pictures to show how far I have come.

[johanr]

Continued...

3. I am planning to taper bricks, likely by using Chipsters method. I don't own a brick saw and will rent one. Would it be advisable to cut all wall bricks according to the tilt angle calculated in the "Pompeii dome calculator" that I found on the forum? Or is that not a good idea and better to rent the saw multiple occasions?
4. How long should the vermicrete set before starting laying the floor and walls?

Looking forward to building the oven!

[johanr]

Finished the dome today! It was good fun to build, but some hard work. The homebrew mortar was like a charm to work with and made it possible work without forms. Although, had I used forms it is likely that I would have had a nicer appearance of the top of the dome. I used the dome calculator to calculate the tilt angle but it did not work that well for the higher courses. My IT was totally useless and I decided to go free and just lay out the bricks, and I assume I somehow drifted making the angles inappropriate and the bricks not fit that well.. I hope the function will still be there. I used the homebrew recipe with sand-lime-clay-cement but 5-1-1-1 instead of 3-1-1-1.
Next will be building the vent, flue and insulation (planning 6 inch vermicrete). I read about heat break between opening vault and vent. How could that be designed and could this be the time to apply such a feature?

[Gulf]

Johanr,

I think your oven will be just fine. I'll let some one else chime in on the "home brew" mix. It think that it will cook great for many years! I don't know why your IT let you down but, that is a mighty fine oven, even with an IT. A simple but effective heat break is to just leave a small gap 1/8th" to 3/16th"between the face of the inner arch and the vent arch. Continue that small gap down in the same plane as the face of the inner through the floor and there it is. A run of flat ceramic fiber tape or small rope and some oven safe heat resistant caulk will make it easier to seal. I see that you have 4" of vcrete under the floor. I did not catch what strength the mix was. Just don't get the mix too strong over the dome. 10-1 (vermiculite-portland cement) is good.

[cobblerdave]

G'day
Sounds like you've done a bit of reading on the homebrew reciepes. The 3:1:1:1 was a bit too stiff on the cementious parts. The 5:1:1:1 is softer and will provide the gasget between the brick units.
The mortars not a glue but rather a gasget which keeps the bricks orientated to form the dome shape. The strength is the dome shape itself, it's one of the strongest structures on the planet along with the arch. Gravity keeps the whole thing together rather than acting to bring it down. There in is its strength over other structures.
Don't worry and enjoy your oven
Regards dave

[johanr]

Thanks for your replies! I felt that 3 parts sand was too little sand in proportion to the cement-clay-lime, and I found some threads supporting that idea (likely some written by you Dave : ). The vermicrete for the base was 5 vermiculite to 1 cement and I plan to use 10-1 for the dome.
I am feeling ambivalent over incorporating a heat break. How big difference does it make/what's the practical reward? If I would instead mortar the vent side and vault to the opening equivalents, then that could provide some (if not much) extra stability for the vent. The vent will comprise of 6 stacked 4.5x9x2.5 on either side, the lowest being in level with the vent floor and the two on the top cut to carry the first vault brick. The vault will be ten bricks wide (bricks on narrow end) and the combined weight will be about 7.5 bricks as 4 are cut in half and 2 are angularly cut. The vent opening will be 57 cm (22.5'') leaving a 3.5 cm (1.5'') of reveal on either side of the opening being 50 cm wide (19.5''). I am glad to get any input on this issue of stability and whether to include a heat break or not. And should ceramic fibres in that case also be put between oven and vent floor bricks?

I am planning to leave the vent floor un-mortared as the rest of the floor. The floor bricks were laid on a bed of sand/clay paste and tapped to level. The sides of the vent will likely be decorated with red standard bricks cut in half alongside its length. That could of course improve vent stability.

Johan

[deejayoh]

Clever use of the magnetic door stop for the IT pivot. I like it!

[david s]

I missed your question about how long to wait before building over the vermicrete layer. the answer is that it will still be wet and will take months to dry out completely. You can use the oven but you will find that its performance will keep on improving as the water is slowly driven out. It will just take a long time. See attached experiment.

[johanr]

Thanks for that info, I started the build 4 days after pouring the vcrete. At that time it was still a bit like cork. Now a week later it feels rock solid.
I decided to include a heat break by leaving 3 mm gap in floor and beteende arches. I will fill that later with ceramic paper 2-3 mm thick (ebay UK) and fill the gap with home brew althouh with extra fine sand (0-2mm). Although, the gap in the floor will be left open and later filled with ash.
Right now, I have finished the sides for the vent arch and will wait 1-2 days before building the arch and chimney.

[johanr]

Also, I skipped water curing the vcrete as I found no info on anyone doing that.

[david s]

Also, I skipped water curing the vcrete as I found no info on anyone doing that.

There is no need to cure the vermicrete because it contains so much extra water that will act to cure it without the need to cover it.

[johanr]

I finished the brick laying today by laying the last bits of the chimney base. It felt really good! I will have a round metal chimney manufactured including base and cap, either in stainless or copper. I drilled some holes in the top chimeny bricks (before laying them) to later attach such a chimney base. Which gives rise to the question: how high should the chimney be? According to the FB plan, I should be fine with a 6'' (15 cm) chimney. I prefer not to have it too tall due to esthetics. Perhaps it is better to go for a lower 8'' chimney instead?

In parallell, I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

[david s]

I finished the brick laying today by laying the last bits of the chimney base. It felt really good! I will have a round metal chimney manufactured including base and cap, either in stainless or copper. I drilled some holes in the top chimeny bricks (before laying them) to later attach such a chimney base. Which gives rise to the question: how high should the chimney be? According to the FB plan, I should be fine with a 6'' (15 cm) chimney. I prefer not to have it too tall due to esthetics. Perhaps it is better to go for a lower 8'' chimney instead?

In parallell, I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

Getting rid of the excess water in the vermicrete is difficult, especially if the layer is thick. It's like a pile of sand that will remain wet for months under the surface. I've found the best way to make a thick layer of vermicrete is to do it in layers of about an inch and a half with a week of sun and wind between each layer, weather permitting, and cover it if it looks like rain. Also found the best ratio is 10:3:1, by volume of vermiculite, water, cement and for every 10 litres (two gallons) of vermiculite add a handful of powdered clay. Vermiculte will vary depending where or who makes it so you may need to adjust the water proportion a little. The finer the grade the more water is required. Also I now use 50/50 vermiculite and perlite which makes a better mix than either of them used alone. If you use more cement then you reduce the insulation value,(see attached doc), less than 10:1 is very difficult to apply vertically.

[Gulf]

.......... I'm planning for to cover the oven in 6'' vermicrete aiming for a perfectly round finish. Any good tips on how to acchieve that easily? I thought to just mix the vermicrete a little stiff and then lay thick (6'') loaves of vermicrete starting from the bottom and go around the dome, working in circles and using a large square trowel to shape it. Is that a good idea, or should I do it differently? Using some sort of form/grid/net? Any suggestions appreciated!

First off, I think that it would be to your advantage to have a blanket between the vcrete and the dome. Aside from the insulation factor, I feel that it acts as an expansion joint. Even if it is only a 1" layer. That out of the way, I used a rotating template to get as close to a perfect sphere as I could. On my template, I attached a homemade curve trowel to the arm. It was attached by drywall screws that allowed me to easily remove and raise it up with each pass.

[Gulf]

Russell (UtahBeehiver) used a similar template, but a little more as a guide. He used a larger curved trowell to actually place the vcrete. And if ya'll haven't seen it go check out his copper clad oven. Here is his photo album. He has also added some finished pics of his oven and stand that were never posted over here. It is well worth the visit .