How I built my pizza oven

[Ultram4]

Thank you!

It was simple. The stones did not stick to each other. A call to the supplier also clarified that refractory mortar should only be used when stones are to be joined horizontally on top of each other and with mortar in the vertical joints. Attempting to build an arch with refractory mortar is therefore not a good idea. It burns extremely slowly and results in weak joints or none at all.

I would claim that there is still no one who knows for sure what the right mortar is, as there aren't many ovens in our country that have been used outdoors for many seasons with large temperature variations (from -20 to +400).

But there is a mixture called "homebrew" that Americans have used and which seems to work well. There are a few variants of it, and the one I chose to use was:

4-5 parts sandbox sand (Byggmax/Jula)
1 part slaked lime (Granngården)
1 part cement (Byggmax)
1 part stove clay (Sunda byggvaror)

In parentheses, I have listed the suppliers where I found the lowest price. Difficult to even find stove clay.

There are also some suppliers who claim to have ready-made mixtures that should work. But I called around quite a bit and talked to the companies' "experts" who all seemed very unsure precisely because there is too little experience.

The good thing about "homebrew" is that it actually worked excellently for masonry and it was much cheaper (one-fifth the cost) than the ready-made special mixes that might not even work. Now we will see how it handles firing and cold winters.

Fantastic oven!

After a visit to Pompeii last month, my partner suddenly became very interested in an outdoor kitchen in the Pompeii style, and after eating some Neapolitan pizzas, a wood-fired oven is a natural feature of this kitchen! 😁

I have also found and seen the Artisan Made pizza oven series, but I have some questions for you.

How has the homebrew mortar held up after a few years?
If you rebuilt it, what would you do differently or adapt?
What did you insulate with?
What are the dimensions of the dome, chimney, and opening?

Very nice build!

 

[zingo]

Thank you!

I haven't had the chance to use the oven more than five times because I immediately started new projects like building a barn 😆

However, I have looked at and "felt" the build quite a bit and haven't seen any issues. Last winter we had 15-18 degrees below freezing for a couple of weeks. It has rained on the dome at times and it's been exposed to high temperatures. But it looks like when I built it.

I bought silicate paint at Hornbach. You were supposed to mix it with some expensive liquid. But I took a chance to skip that. And it has stayed put and hasn't shown any algae growth or come off anywhere despite the weather. So the reviews you see on Hornbach's website seem odd.

I've insulated with about 10 cm vermikulit on the dome and 15 cm vermikulit under the slab.

The only thing I would have done differently is the slope of the slab. I didn't think about the rainwater possibly running into the oven when it rains sideways. So I should have sloped the slab a couple of degrees outward. Now, I did build a weather protection that catches 99% of all the water. And it does dry up quickly when you fire it up a bit.

I can measure the dome and other things tonight.
Will get back to you.

 

[Vardagsrum]

This might be one of the finest things I've seen here on Byggahus. And maybe even on YouTube!

Thank you for sharing your first-class project and with such great documentation too! I liked that the pictures you took were from a "fixed-mounted" camera.

Do you have any detail or close-up pictures of the chimney? How has it worked, does it evacuate smoke well?

I like that you made such a large "manlucka" for easy access during inspection and possible repairs.

How do you measure the temperature?

Maybe not traditional, but would some form of reflector result in shorter heating/cooking time?

Again, great to see, well done!

 

[zingo]

This might be one of the finest things I've seen here on Byggahus. And maybe even on YouTube!

Thank you for sharing your first-class project and with such good documentation too! I liked that the pictures you took came from a "fixed-mounted" camera.

Do you have any detailed or close-up pictures of the chimney? How has it worked, does it evacuate the smoke well?

I like that you've made such a large "manhole," for easy access during inspections and potential repairs.

How do you measure the temperature?

Maybe not traditional, but could some form of reflector shorten the heating/cooking time?

Again, fun to see, great job!

Thank you! Kind words 😃

I think the chimney works quite well, but as mentioned, I haven't tried it enough times yet.
I treated myself to a BOSCH IR-thermometer. It's available at Jula: https://www.jula.se/catalog/verktyg...nstrument/ir-termometrar/ir-termometer-026399

I don't have any close-ups right now, but I can take some tonight 😊 The joints have started to weather, probably because I used regular mortar. I didn't have any homebrew left and took a chance. Or maybe I mixed it poorly.

Perhaps a reflector could work well. Interesting thought.

 

[Vardagsrum]

Did you use regular B or C-grade mortar for the chimney?

I can't see why your joints would crumble, assuming you've done a good job, which it really looks like you have!

Apart from burning oak that hasn't dried for long enough (2-3 summers), mortar (unintentional pun) doesn't usually crumble significantly.

In my humble opinion, the crumbling of mortar over time is mainly due to three factors:

1: Aggressive and stressed chimney sweeper with too large tools and too heavy weights that are thrown down, making a racket throughout the flue. Eventually, both the mortar and any plaster will come loose.

2: Condensation from flue gases with too low a temperature. This problem worsens the wetter the wood is and the colder the chimney the smoke has to pass through. If you put in 15kg of wood with a moisture content of, say, 30%, then it's 4.5 liters of "water" that needs to pass through the chimney. If you put in wood at 18%, then it's 2.7 liters that need to be released.

If the top of the chimney is too cold, the water vapor condenses and runs down the inside.

The condensate also contains many unpleasant substances, including sulfur-containing ones that are directly corrosive to the mortar.

3: Intruding moisture from above in the form of rain/snow. If you don't use your chimney particularly often, it won't have time to dry out sufficiently. This can cause crumbling from frost damage. It's usually not a problem for those who regularly burn wood/pellets, though.

I'm talking about "regular" chimneys for solid fuel boilers, to be clear, but I can't see that there would be any principal difference.

Number 1 won't be relevant for you because you will sweep it yourself 😊

Number 2 won't be relevant for you, because you understand to burn only dry wood, and the flue gases in your very short chimney will be very warm.

Number 3 won't be relevant for you either, because you understood to make a cover for the chimney.

The only potential problem I could see in the future is just the temperature of your flue gases. It feels like they can be very high, depending on the wood and the amount of wood used?

An "embedded" flue gas thermometer would mar the oven, but it would be good to make sure what temperature you're actually sending through the chimney. You could try hanging a meat thermometer a bit down the chimney while running the oven sometime and see where you land.

Chimneys can handle a lot, but over 350° I don't think you should go in terms of flue gas temperature.

But as long as you have a good oxygen supply (never smolder), dry wood, good draft without too high flue gas temperature, I think it will work fine. Just take it easy during the oven's warm-up phase!

With such a fine oven as yours, I would heat it up slowly, start with fine sticks and wait for a bed of coals, then add slightly thicker ones, wait, then add even thicker ones, etc. In winter, I would start it up very gently.

I wouldn't be afraid of burning pine or fir in it; where did you get the information that these would contain any significant amount of acid?

However, they do spark, of course, and you might not want more ash or wood chips in your pizza than necessary 🙂 But I wouldn't be shy to start with them. It depends on the frequency of use, of course!

Aspen and alder wood can also be nice to burn, I recommend you try them. They don't give as much heat as birch per kg, but they burn steadily and evenly and leave very little soot/tar. Some say that aspen even burns away soot.

Well, I won't go on about wood or chimneys any longer, but I wanted to share some of my beliefs, hoping you and your fine oven can benefit from one of them.

One question though, is it the temperature of the actual bottom plate that you want to measure when starting to bake these delicacies, or does the air temperature also play a role?

And the last and most important question:

Do the pizzas turn out delicious? 😉

 

[zingo]

Did you use regular B, or C-mortar to the chimney do you mean?

I can't see why your joints would crumble.. Assuming you did a good job and it really looks like you did!

Apart from burning oak that hasn't dried long enough (2-3 summers), mortar (unintentional pun) doesn't usually crumble significantly.

In my humble opinion, the crumbling over time is mainly due to three different factors:

1: An aggressive and stressed chimney sweep with too large a tool and too heavy a weight, which is thrown down so it just rings through the entire flue. Eventually, both plaster and any mortar will come off.

2: Condensation of flue gases with too low a temperature. The problem worsens the wetter the wood is and the colder the chimney the smoke must pass through. If you put in 15kg of wood with a moisture content of, for example, 30%, that's 4.5 liters of "water" that needs to pass through the chimney. If you use wood at 18%, then 2.7 liters need to come out.

If the top of the chimney is too cold, the water vapor will condense and run downwards inside.

The condensate also contains many unpleasant substances, including sulfurous ones that are directly corrosive to mortar.

3: Penetrating moisture from above in the form of rain/snow. If you don't use your chimney very often, it doesn't get a chance to dry out sufficiently. Then it can crumble due to frost shattering. Often no problem for those who regularly burn wood/pellets though.

Now I'm talking about “standard” chimneys for solid fuel boilers, I should add, but I don't see why there would be any fundamental difference.

Number 1 doesn't apply to you because you will clean the chimney yourself 😊

Number 2 doesn't apply to you either because you understand to only burn dry wood and also the flue gases in your very short chimney will be very hot.

Number 3 doesn't apply to you either because you understood to make a roof over the chimney.

The only thing I could foresee potentially becoming an issue in the future is just the temperature of your flue gases. It seems that depending on the wood and the amount of wood, they could be very high?

Now, an “integrated” flue gas thermometer would spoil the look of the oven, but it would be good to ensure what temperature you’re actually sending out through the chimney. You could try hanging a meat thermometer a bit down the chimney when you run the oven sometime and see where you end up.

Chimneys can handle a lot, but over 350°C, I don't think you should go in flue gas temperature.

But as long as you have good oxygen supply (never smolder), dry wood, good draw without having too high flue gas temperature, I think it will work fine. As long as you take it easy during the heating phase of the oven!

With such a beautiful oven as yours, I would fire it up slowly, start with fine kindling and wait for embers, then add slightly thicker wood, wait, add even thicker, and so on. In the winter, I would start it really gently.

And I wouldn't be afraid to burn spruce or pine in it, where did you get the information that these would contain any significant amount of acid?

However, it's true that these types might spark, and you might not want more ash or wood splinters in your pizza than necessary 🙂 But I wouldn't hesitate to use them to light a fire. However, this also depends on the frequency of use!

Aspen and alder wood can also be nice to burn with, I recommend you try them. They don’t give as much heat as birch per kg, but they burn calmly and evenly and leave very little soot/tar. Some even say aspen burns away soot.

Well, let me not go on about wood or chimneys any longer, but I wanted to add some of my beliefs, hoping that you and your fine oven can benefit from one of them.

A question though, is it the temperature on the actual bottom plate you want to measure when you start baking these delicacies, or does the air temperature also matter?

And the last and most important question:

Do the pizzas turn out great? 😉

I mixed my own with cement and sand, pretty much the last I had left in the bags to get any sort of chimney at all. It was the last step. So I had planned from the start to redo it.

I don’t know anywhere near as much as you do about flue gases, chimneys and mortar. I've pieced together the facts I’ve found and been forced upon over the years.

And I’ve fired exactly as you describe. First thin kindling, then a bit thicker until the fire sustains itself. Then I gradually add thicker wood until it’s really going.

Yes, it’s the bottom plate I measure before putting in the pizzas because apparently that’s how you get crispy, quickly heated bottoms. Then I move the hearth to the other side and fire even more so that the warm air is thrown down onto the pizza’s surface and heats it just as intensely.

The pizzas turn out very well. But I haven’t had time to experiment with the dough/rising, so that the dough turns out good. It's just as important as having a good oven 🤓

 

[Ultram4]

Thank you!

I haven't had the chance to use the oven more than five times because I immediately started new projects, like building a barn 😆

However, I've looked at and "felt" the build quite a lot and haven't seen any issues. Last winter we had temperatures of 15-18 degrees below zero for a couple of weeks. It's rained on the dome at times and it has been exposed to high temperatures. But it looks the same as when I built it.

I bought silicate paint at Hornbach. You were supposed to mix it with some expensive liquid. But I took a chance on avoiding that. And it has held like rock and hasn't had any algae growth or peeled anywhere despite weather and wind. So the reviews you see on Hornbach's website feel odd.

I've insulated with about 10 cm of vermiculite on the dome and 15 cm of vermiculite under the slab.

The only thing I would have done differently is the slope of the slab. I didn't think about rainwater possibly running into the oven when it's raining sideways. So I should have tilted the slab a couple of degrees outward. Now, I built a weather protection that takes care of 99% of all water. And it dries quickly when you fire it up a bit.

Can measure the dome and other parts this evening.
Will get back to you.

Thanks for the response!

It makes sense to tilt the slab slightly for drainage. Here in Skåne, winter is mostly rain and wind, so I'll keep that functionality in mind.

Were you ever considering using ceramic fiber as insulation, and if so, why did you opt against it?

Looking forward to your measurements! 😁

 

[zingo]

Thanks for the reply!

It makes sense to tilt the slab slightly for drainage. Here in Skåne, winter is mostly rain and wind, so I'll take that feature with me.

Did you ever consider using ceramic blanket as insulation and if so, what was the reason you decided against it?

Looking forward to your dimensions! 😁

Opening 54 wide, 32 high
Dome 130 outer diameter, 97 inner.
Chimney 40 wide, 30 high, but I plan to extend it to 50-60 eventually.