DIY Steel and brick WFO

[pyropizza]

Hi, hope this is in the right place.

I'm looking to weld a Mild Steel or Stainless Steel pizza oven.

I want it to be split level where the fire is below, and the pizza shelf above with a gap at the back of the pizza shelf to let heat through and over the pizza to the front. Similar to this...

www.youtube.com/watch?v=Ik6Slb8e_VM

...but steel not brick. The shelves will be tight fitting but height adjustable to adjust the heat. Will experiment with top shelf material when built - steel or stone.

So will basically be a metal box with the front missing (except the top edge), one fire shelf that is full depth and one cooking shelf that is not full depth.

I'm ok making this myself but would like to enclose it with a standard brick built surround to stop dogs and kids melting their faces on the metal that will, no doubt, get red hot.

Would a sand base with fire brick "feet", and surround made with standard bricks and mortar with a slab lid work, and if so what size should the voids be and what should they be filled with? Neat perlite? Would the filler/insulation be ok bottom, sides and top?

I'm not too concerned with the insulation properties adding to the oven temperature (I think), because the fire being below the shelf and height adjustable, I'm more concerned with protecting noses and fingers from 3 sides at least and protecting the bricks and mortar from cracking/exploding.

Any help much appreciated!

[downunderdave]

Apr 17, 2022 11:07:53 GMT pyropizza said:

Hi, hope this is in the right place.

I'm looking to weld a Mild Steel or Stainless Steel pizza oven.

I want it to be split level where the fire is below, and the pizza shelf above with a gap at the back of the pizza shelf to let heat through and over the pizza to the front. Similar to this...

www.youtube.com/watch?v=Ik6Slb8e_VM

...but steel not brick. The shelves will be tight fitting but height adjustable to adjust the heat. Will experiment with top shelf material when built - steel or stone.

So will basically be a metal box with the front missing (except the top edge), one fire shelf that is full depth and one cooking shelf that is not full depth.

I'm ok making this myself but would like to enclose it with a standard brick built surround to stop dogs and kids melting their faces on the metal that will, no doubt, get red hot.

Would a sand base with fire brick "feet", and surround made with standard bricks and mortar with a slab lid work, and if so what size should the voids be and what should they be filled with? Neat perlite? Would the filler/insulation be ok bottom, sides and top?

I'm not too concerned with the insulation properties adding to the oven temperature (I think), because the fire being below the shelf and height adjustable, I'm more concerned with protecting noses and fingers from 3 sides at least and protecting the bricks and mortar from cracking/exploding.

Any help much appreciated!

I’m all for experimenting and trying alternatives, but have learnt from experience after building two different designs, both of which worked ok, but I ended up building the traditional hemisphere with a cross draft front flue is by far the better design. Using refractory or brick gives the best performance as the thermal conductivity is in the best range. Ie once heated it will retain its heat well, while also having the ability to store heat (high thermal mass). By contrast steel, whether mild or stainless has a far higher thermal conductivity which both heats and cools very fast. Unfortunately this leads to great difficulty in keeping the oven at a consistent temperature, as well as not being able to use the oven for retained heat cooking because of its lower (than brick or refractory) thermal mass.
Wood fired ovens have been around for a few thousand years in the current design. There must have been many thousands of attempts to improve the design, yet the current hemisphere with front flue still dominates. I don’t want to stop you from innovating and the best way to learn is to build one, learn from how it performs, then build another. It’s a fascinating topic, full of problems and possible solutions. You must insulate both under and over the oven to achieve any kind of performance. Sand is a poor insulator. A steel cooking surface is non porous leading to soggy pizza bases.

[pyropizza]

Apr 18, 2022 6:35:38 GMT downunderdave said:

Apr 17, 2022 11:07:53 GMT pyropizza said:

Hi, hope this is in the right place.

I'm looking to weld a Mild Steel or Stainless Steel pizza oven.

I want it to be split level where the fire is below, and the pizza shelf above with a gap at the back of the pizza shelf to let heat through and over the pizza to the front. Similar to this...

www.youtube.com/watch?v=Ik6Slb8e_VM

...but steel not brick. The shelves will be tight fitting but height adjustable to adjust the heat. Will experiment with top shelf material when built - steel or stone.

So will basically be a metal box with the front missing (except the top edge), one fire shelf that is full depth and one cooking shelf that is not full depth.

I'm ok making this myself but would like to enclose it with a standard brick built surround to stop dogs and kids melting their faces on the metal that will, no doubt, get red hot.

Would a sand base with fire brick "feet", and surround made with standard bricks and mortar with a slab lid work, and if so what size should the voids be and what should they be filled with? Neat perlite? Would the filler/insulation be ok bottom, sides and top?

I'm not too concerned with the insulation properties adding to the oven temperature (I think), because the fire being below the shelf and height adjustable, I'm more concerned with protecting noses and fingers from 3 sides at least and protecting the bricks and mortar from cracking/exploding.

Any help much appreciated!

I’m all for experimenting and trying alternatives, but have learnt from experience after building two different designs, both of which worked ok, but I ended up building the traditional hemisphere with a cross draft front flue is by far the better design. Using refractory or brick gives the best performance as the thermal conductivity is in the best range. Ie once heated it will retain its heat well, while also having the ability to store heat (high thermal mass). By contrast steel, whether mild or stainless has a far higher thermal conductivity which both heats and cools very fast. Unfortunately this leads to great difficulty in keeping the oven at a consistent temperature, as well as not being able to use the oven for retained heat cooking because of its lower (than brick or refractory) thermal mass.
Wood fired ovens have been around for a few thousand years in the current design. There must have been many thousands of attempts to improve the design, yet the current hemisphere with front flue still dominates. I don’t want to stop you from innovating and the best way to learn is to build one, learn from how it performs, then build another. It’s a fascinating topic, full of problems and possible solutions. You must insulate both under and over the oven to achieve any kind of performance. Sand is a poor insulator. A steel cooking surface is non porous leading to soggy pizza bases.

Thanks Dave, to be honest, the only reason I began going through different ideas to the norm is the fear of fire bricks getting wet and frost damage, and having to rebuild which led me to thinking about steel.

If I could build a more traditional design but which enabled me to replace the fire bricks easily if they got damaged I'd feel much more confident.

Which leads me to plan B (well I'm probably on at least Plan M but plan B for here).

The initial question is, can firebricks be used without mortar/cement/screed and still protect insulation and standard bricks if packed tightly and keep in enough heat for cooking?

I'm thinking steel mesh or steel angle iron to hold the bricks instead of mortar but built in such a way I can cut and reweld or slide bricks out to replace if needed without having to rebuild the standard brick outer layer and insulation.

[downunderdave]

Apr 18, 2022 12:13:59 GMT pyropizza said:

Apr 18, 2022 6:35:38 GMT downunderdave said:

I’m all for experimenting and trying alternatives, but have learnt from experience after building two different designs, both of which worked ok, but I ended up building the traditional hemisphere with a cross draft front flue is by far the better design. Using refractory or brick gives the best performance as the thermal conductivity is in the best range. Ie once heated it will retain its heat well, while also having the ability to store heat (high thermal mass). By contrast steel, whether mild or stainless has a far higher thermal conductivity which both heats and cools very fast. Unfortunately this leads to great difficulty in keeping the oven at a consistent temperature, as well as not being able to use the oven for retained heat cooking because of its lower (than brick or refractory) thermal mass.
Wood fired ovens have been around for a few thousand years in the current design. There must have been many thousands of attempts to improve the design, yet the current hemisphere with front flue still dominates. I don’t want to stop you from innovating and the best way to learn is to build one, learn from how it performs, then build another. It’s a fascinating topic, full of problems and possible solutions. You must insulate both under and over the oven to achieve any kind of performance. Sand is a poor insulator. A steel cooking surface is non porous leading to soggy pizza bases.

Thanks Dave, to be honest, the only reason I began going through different ideas to the norm is the fear of fire bricks getting wet and frost damage, and having to rebuild which led me to thinking about steel.

If I could build a more traditional design but which enabled me to replace the fire bricks easily if they got damaged I'd feel much more confident.

Which leads me to plan B (well I'm probably on at least Plan M but plan B for here).

The initial question is, can firebricks be used without mortar/cement/screed and still protect insulation and standard bricks if packed tightly and keep in enough heat for cooking?

I'm thinking steel mesh or steel angle iron to hold the bricks instead of mortar but built in such a way I can cut and reweld or slide bricks out to replace if needed without having to rebuild the standard brick outer layer and insulation.


Yes, kilns are often built without mortar, in fact it has the advantage of allowing the bricks to expand independently. Any gaps between bricks can increase heat loss and they usually need steel bracing to hold them together.
Building something without mortar allows you to easily alter and rebuild. I suggest you build something to see how it goes, many materials can be obtained free or cheaply. Controlling the fire is fun and addictive, it sounds like you are embarking on a fascinating journey.

[pyropizza]

Apr 18, 2022 23:27:36 GMT downunderdave said:

Apr 18, 2022 12:13:59 GMT pyropizza said:

Thanks Dave, to be honest, the only reason I began going through different ideas to the norm is the fear of fire bricks getting wet and frost damage, and having to rebuild which led me to thinking about steel.

If I could build a more traditional design but which enabled me to replace the fire bricks easily if they got damaged I'd feel much more confident.

Which leads me to plan B (well I'm probably on at least Plan M but plan B for here).

The initial question is, can firebricks be used without mortar/cement/screed and still protect insulation and standard bricks if packed tightly and keep in enough heat for cooking?

I'm thinking steel mesh or steel angle iron to hold the bricks instead of mortar but built in such a way I can cut and reweld or slide bricks out to replace if needed without having to rebuild the standard brick outer layer and insulation.


Yes, kilns are often built without mortar, in fact it has the advantage of allowing the bricks to expand independently. Any gaps between bricks can increase heat loss and they usually need steel bracing to hold them together.
Building something without mortar allows you to easily alter and rebuild. I suggest you build something to see how it goes, many materials can be obtained free or cheaply. Controlling the fire is fun and addictive, it sounds like you are embarking on a fascinating journey.

Thanks again. I might go with that then and have an experiment.

Another idea was a steel drum/fire brick combo. Would a drum on its side part filled with refractory and fire bricks to create a base and then a fire brick arch OUTSIDE the top of the barrel with insulation and a red brick arch over that work or would the fire brick top need to be inside the drum too? Bit concerned with the space if I pack everything inside.

I might make my mind up soon.

Also, if I was going to go with Plan B and not use mortar, I have a rough plan for the steel which I think will work but two questions.

1. Would simply using steel supports, loose fire brick dome, 1-2 inch insulation and then a red brick top be enough or would a refractory cement layer be needed too between the insulation and red brick?

2. What would best be done with the 'open' edge between the layers of fire and red bricks. Difficult to explain what I mean but if I do loose fire bricks with a red brick dome over then at some point I will have an open edge leaving the insulation exposed, would this need to be screeded over in some way or would making the two types of brick taper in and meet towards the front edge be ok without too much heat transfer?

[pyropizza]

To expand on the barrel idea I've created an amazing drawing which begs the question why I got an E in art 20 odd years ago...

ibb.co/SsW9gwG

In step 1,
- I want to use one layer of firebricks for the whole floor not mortared in so I can replace easily if necessary.
- create one arch of fire bricks at the front to create the 62%, these bricks will be on welded angle iron with no mortar again so easy to replace.

In step 2,
- add firebricks to the remaining part of the barrel but on the outside of the barrel. Held in place lightly by steel straps, would not be easily replaceable because of the following layers but able to expand and move.
- maybe replace this section of fire bricks with perlite concrete as won't be seen, will be protected by following layers and food is protected by the steel barrel??
- once done, cover this layer, including the front of the barrel with insulation (ceramic fibre?)

In step 3,
- add red brick to the entire structure to protect from weather.

The idea is the firebricks at the front inside will create the 62%, these and the external firebricks or perlite concrete will create the thermal mass and the ceramic fibre and red bricks will create the insulation and protection. Also the steel drum will protect the food from any debris and stop the dome/arch from failing and all visible firebricks are easily replaced. (And the other part of the drum can be made into a BBQ). I will make a door too and do the chimney in step 1.

Is this looking ok or am I completely off track?

[downunderdave]

Apr 19, 2022 15:07:42 GMT pyropizza said:

To expand on the barrel idea I've created an amazing drawing which begs the question why I got an E in art 20 odd years ago...

ibb.co/SsW9gwG

In step 1,
- I want to use one layer of firebricks for the whole floor not mortared in so I can replace easily if necessary.
- create one arch of fire bricks at the front to create the 62%, these bricks will be on welded angle iron with no mortar again so easy to replace.

In step 2,
- add firebricks to the remaining part of the barrel but on the outside of the barrel. Held in place lightly by steel straps, would not be easily replaceable because of the following layers but able to expand and move.
- maybe replace this section of fire bricks with perlite concrete as won't be seen, will be protected by following layers and food is protected by the steel barrel??
- once done, cover this layer, including the front of the barrel with insulation (ceramic fibre?)

In step 3,
- add red brick to the entire structure to protect from weather.

The idea is the firebricks at the front inside will create the 62%, these and the external firebricks or perlite concrete will create the thermal mass and the ceramic fibre and red bricks will create the insulation and protection. Also the steel drum will protect the food from any debris and stop the dome/arch from failing and all visible firebricks are easily replaced. (And the other part of the drum can be made into a BBQ). I will make a door too and do the chimney in step 1.

Is this looking ok or am I completely off track?


Firstly be careful about sourcing a steel drum. The typical 44 gallon drum is mild steel and prone to rusting. In addition a really common accident around the world results in many deaths every year from people cutting oil drums which can explode if ignited, typically by an angle grinder, or oxy torch. They must be washed out really thoroughly with detergent first. If you can find a stainless one, maybe a large beer keg, it would be worth the search and expense.

As steel is far more conductive than brick or refractory it will expand before the brick or refractory even has a chance to warm up. If you place bricks against the steel curve of the barrel there will only be one contact point for each brick which will reduce conductive heat transfer to a minimum. This is likely to result in slow heat up time of the total oven mass.


Vermicrete produces a lightweight concrete and is unsuitable if you want to increase the thermal mass. (see attached table) It is great for insulation but lousy for increasing strength and thermal mass.


A half barrel oven may appear to be simple to construct, but is an unstable form when subjected to thermal expansion, unlike the hemisphere which is a self supporting structure. Barrel arches usually require either steel bracing, buttressing or both.

[pyropizza]

Apr 19, 2022 21:41:28 GMT downunderdave said:

Apr 19, 2022 15:07:42 GMT pyropizza said:

To expand on the barrel idea I've created an amazing drawing which begs the question why I got an E in art 20 odd years ago...

ibb.co/SsW9gwG

In step 1,
- I want to use one layer of firebricks for the whole floor not mortared in so I can replace easily if necessary.
- create one arch of fire bricks at the front to create the 62%, these bricks will be on welded angle iron with no mortar again so easy to replace.

In step 2,
- add firebricks to the remaining part of the barrel but on the outside of the barrel. Held in place lightly by steel straps, would not be easily replaceable because of the following layers but able to expand and move.
- maybe replace this section of fire bricks with perlite concrete as won't be seen, will be protected by following layers and food is protected by the steel barrel??
- once done, cover this layer, including the front of the barrel with insulation (ceramic fibre?)

In step 3,
- add red brick to the entire structure to protect from weather.

The idea is the firebricks at the front inside will create the 62%, these and the external firebricks or perlite concrete will create the thermal mass and the ceramic fibre and red bricks will create the insulation and protection. Also the steel drum will protect the food from any debris and stop the dome/arch from failing and all visible firebricks are easily replaced. (And the other part of the drum can be made into a BBQ). I will make a door too and do the chimney in step 1.

Is this looking ok or am I completely off track?


Firstly be careful about sourcing a steel drum. The typical 44 gallon drum is mild steel and prone to rusting. In addition a really common accident around the world results in many deaths every year from people cutting oil drums which can explode if ignited, typically by an angle grinder, or oxy torch. They must be washed out really thoroughly with detergent first. If you can find a stainless one, maybe a large beer keg, it would be worth the search and expense.

As steel is far more conductive than brick or refractory it will expand before the brick or refractory even has a chance to warm up. If you place bricks against the steel curve of the barrel there will only be one contact point for each brick which will reduce conductive heat transfer to a minimum. This is likely to result in slow heat up time of the total oven mass.


Vermicrete produces a lightweight concrete and is unsuitable if you want to increase the thermal mass. (see attached table) It is great for insulation but lousy for increasing strength and thermal mass.


A half barrel oven may appear to be simple to construct, but is an unstable form when subjected to thermal expansion, unlike the hemisphere which is a self supporting structure. Barrel arches usually require either steel bracing, buttressing or both.


ok, sounds like plan d or e tomorrow. I'll have to see. thanks for all the help

[pyropizza]

Apr 19, 2022 21:41:28 GMT downunderdave said:

Apr 19, 2022 15:07:42 GMT pyropizza said:

To expand on the barrel idea I've created an amazing drawing which begs the question why I got an E in art 20 odd years ago...

ibb.co/SsW9gwG

In step 1,
- I want to use one layer of firebricks for the whole floor not mortared in so I can replace easily if necessary.
- create one arch of fire bricks at the front to create the 62%, these bricks will be on welded angle iron with no mortar again so easy to replace.

In step 2,
- add firebricks to the remaining part of the barrel but on the outside of the barrel. Held in place lightly by steel straps, would not be easily replaceable because of the following layers but able to expand and move.
- maybe replace this section of fire bricks with perlite concrete as won't be seen, will be protected by following layers and food is protected by the steel barrel??
- once done, cover this layer, including the front of the barrel with insulation (ceramic fibre?)

In step 3,
- add red brick to the entire structure to protect from weather.

The idea is the firebricks at the front inside will create the 62%, these and the external firebricks or perlite concrete will create the thermal mass and the ceramic fibre and red bricks will create the insulation and protection. Also the steel drum will protect the food from any debris and stop the dome/arch from failing and all visible firebricks are easily replaced. (And the other part of the drum can be made into a BBQ). I will make a door too and do the chimney in step 1.

Is this looking ok or am I completely off track?


Firstly be careful about sourcing a steel drum. The typical 44 gallon drum is mild steel and prone to rusting. In addition a really common accident around the world results in many deaths every year from people cutting oil drums which can explode if ignited, typically by an angle grinder, or oxy torch. They must be washed out really thoroughly with detergent first. If you can find a stainless one, maybe a large beer keg, it would be worth the search and expense.

As steel is far more conductive than brick or refractory it will expand before the brick or refractory even has a chance to warm up. If you place bricks against the steel curve of the barrel there will only be one contact point for each brick which will reduce conductive heat transfer to a minimum. This is likely to result in slow heat up time of the total oven mass.


Vermicrete produces a lightweight concrete and is unsuitable if you want to increase the thermal mass. (see attached table) It is great for insulation but lousy for increasing strength and thermal mass.


A half barrel oven may appear to be simple to construct, but is an unstable form when subjected to thermal expansion, unlike the hemisphere which is a self supporting structure. Barrel arches usually require either steel bracing, buttressing or both.


....and just to make sure - is the only thing that creates thermal mass the fire bricks? or can refractory concrete be used too (without perlite/vermiculite)?

[downunderdave]

"....and just to make sure - is the only thing that creates thermal mass the fire bricks? or can refractory concrete be used too (without perlite/vermiculite)?"

No it's not the only thing. An old Italian trick to increase the thermal mass in their ovens was to throw in a couple of truck axles into the oven if they wanted more thermal mass for extended cooking time. A product called dense castable refractory that is widely used in industry, largely replacing firebricks would be the normal choice, high strength and good thermal mass. It is usually gunned in place but can also be troweled. I use it every second day. It does have drawbacks though, it contains calcium aluminate cement which goes off really fast leaving very little working time if troweled into position. It is also really expensive and contains high temperature aggregates that are really not necessary for the temperature range of an oven. Because the chemistry is different (calcium aluminate) it achieves full strength in 24 hrs (I give it at least 48).

A far cheaper alternative which works very well is what we call homebrew. The recipe is 3:1:1:1 9by volume) sand, Portland cement, hydrated lime, powdered clay mixed to ball up consistency. Some very fine polypropylene fibres (as used in the concrete industry, should be added. These melt at 160C and leave behind a network of tiny pipes that moisture can find its way through to the surface. This reduces the likelihood of steam spalling. These fibres are already added to the proprietary castable refractory, but you'd need to add them to a brew you make yourself.

[pyropizza]

Apr 20, 2022 0:42:27 GMT downunderdave said:

"....and just to make sure - is the only thing that creates thermal mass the fire bricks? or can refractory concrete be used too (without perlite/vermiculite)?"

No it's not the only thing. An old Italian trick to increase the thermal mass in their ovens was to throw in a couple of truck axles into the oven if they wanted more thermal mass for extended cooking time. A product called dense castable refractory that is widely used in industry, largely replacing firebricks would be the normal choice, high strength and good thermal mass. It is usually gunned in place but can also be troweled. I use it every second day. It does have drawbacks though, it contains calcium aluminate cement which goes off really fast leaving very little working time if troweled into position. It is also really expensive and contains high temperature aggregates that are really not necessary for the temperature range of an oven. Because the chemistry is different (calcium aluminate) it achieves full strength in 24 hrs (I give it at least 48).

A far cheaper alternative which works very well is what we call homebrew. The recipe is 3:1:1:1 9by volume) sand, Portland cement, hydrated lime, powdered clay mixed to ball up consistency. Some very fine polypropylene fibres (as used in the concrete industry, should be added. These melt at 160C and leave behind a network of tiny pipes that moisture can find its way through to the surface. This reduces the likelihood of steam spalling. These fibres are already added to the proprietary castable refractory, but you'd need to add them to a brew you make yourself.

so would replacing the fire bricks i planned on put on the outside of the barrel with home brew work with stainless steel or would expansion be a problem there too?

[downunderdave]

Yes, expansion will still be a problem. It would be better IMHO to build a sand castle hemisphere covered in wet newspaper with the homebrew troweled over it. That way you'd have a more stable structure, cast in situ with no expanding steel liner causing expansion or corrosion problems.

[pyropizza]

Apr 20, 2022 1:50:56 GMT downunderdave said:

Yes, expansion will still be a problem. It would be better IMHO to build a sand castle hemisphere covered in wet newspaper with the homebrew troweled over it. That way you'd have a more stable structure, cast in situ with no expanding steel liner causing expansion or corrosion problems.

Ok, after going around the houses I'll do it properly

So, is home brew 'non explosive'? so many horror stories of concrete exploding under heat led me to steel and fire bricks.

How thick a home brew layer? and then what goes over that and how thick should those layers be?

Heard lots of contradictions of collapses due to damp/frost so that was another reason of thinking about steel etc.

Should the base be made of the same and again how thick and what layers above/below?

I realise there's YouTube videos etc that go through this but a lot I've seen so far contradict what you're saying because they're cutting corners to get YouTube views and I'd rather get advice from you rather than someone stuffing foil, mud and sand in rusting barrels and it's difficult separating the facts from the corner cutting/dangerous/inefficient malarkey elsewhere

[downunderdave]

Homebrew is not explosive. Steam spalling is possible if the moisture is driven off too fast, particularly if the burnout fibres are not added.
Thickness is generally 50mm
The floor should be firebrick, again 50mm same as wall dome thickness, the homebrew is ok for the dome but not the floor.
The youtube videos are usually made by people who have no experience with wood fired ovens, most of them won't last long.

There are some well documented homebrew builds on this forum , but many more on "other ovens" in

community.fornobravo.com

Plenty of research will save you money and heartache.

[pyropizza]

Apr 20, 2022 5:13:54 GMT downunderdave said:

Homebrew is not explosive. Steam spalling is possible if the moisture is driven off too fast, particularly if the burnout fibres are not added.
Thickness is generally 50mm
The floor should be firebrick, again 50mm same as wall dome thickness, the homebrew is ok for the dome but not the floor.
The youtube videos are usually made by people who have no experience with wood fired ovens, most of them won't last long.

There are some well documented homebrew builds on this forum , but many more on "other ovens" in

community.fornobravo.com

Plenty of research will save you money and heartache.

Ok, thanks for all the help