Tweet
Hi all, I've found this forum invaluable in researching for my upcoming Pompeii oven build. I'm looking at using (from the bottom up 100 reinforced concrete slab, ceramic ties (to aid airflow to weep holes), 75 Hebel panel, 25mm Cal Si board with 75mm refractory bricks as my cooking surface. Does anybody see any issues with that? Secondly, and the main reason for my query, is about the front gallery and arch section. I would like to build my side gallery bricks on a slight angle, increasing space and visibility into the oven as per my picture attached. I know this will make building the gallery arch more difficult. I would like to insulate between the cooking dome and the gallery arch section with FB and Cal Si board (as per photo). I expect that this would reduce radiant heat around the work area whilst reducing the heat sink affect the front arch may have. I am also considering building a custom manifold to attach the flue too. The manifold would be the full width of the arch and approx 180mm deep transitioning to a 150mm flue approx 1400mm tall. I'm expecting this will reduce the possibility of smoke travel out under the front arch and discolouring the facade.
I'm looking at pouring my suspended slab within the next month and am happy to upload my progress pictures for you all to critique.
Thank you in advance.
Dragan
Hi Dragan,
what size internal diameter are you planning?
Also, is it to be a brick build or cast?
Dave
Hi David,
I'm planning on having an internal diameter of 900mm and will be using refractory bricks for the dome. Originally I was thinking about cutting every brick to minimize internal and external gaps but after much research it seems the effort to do that may not be of great benefit so I will simply concentrate on making the internal joins small.
Decisions on the amount of cutting to do can often depend on whether you buy a wet saw or rent one. If you buy you can cut bricks at your leisure, making the required angles as the build progresses, but if you rent you’ll probably cut all your bricks in half and adjust the mortar gaps as you build.
Contrary to most builders here who aim for tight and precise joints, the famous kiln builder Daniel Rhodes, the author of Kilns, generally regarded as the kiln builders bible, he states,
"In kiln building it is much better to have a loose structure than a tight one. For this reason the amateur may have a slight advantage over the professional mason. Because his bricklaying is apt to be somewhat loose and not tightly locked together I have seen kilns made by professional bricklayers which in use suffered severe cracking and swelling due to the overly tight and precise workmanship and lack of expansion joints."
We're not building kilns here and our ovens only experience about half the thermal expansion of a kiln, however the same principles apply.
Interesting! I think I'll cut my side angles and fill under the back of each row with the proper mortar, thank you. What are your thoughts regarding the 25mm CalSil board placed between the dome and the gallery arch?
Here is a photo of what I have built so far. I precast my own 50mm concrete top which are still to be polished a little. Under top storage for wood, charcoal etc. I might end up putting a couple of doors to close in one section in the future. The pizza oven will go in the corner section once I've poured my slab.
I'm not sure what you mean by "proper mortar", but most of the proprietary refractory mortars recommend very thin mortar joints, which would be contrary to filling the outside gaps, as well as going through a lot of expensive mortar.
Your set up looks great, I'm doing a polished concrete table beside my oven at the moment, it's messy and painstaking work and hard to know when to stop.
Putting doors on the wood storage area will make things look pretty, but has the unfortunate result in keeping the wood damp, especially in an uncovered outdoor area.
Regarding the calsil between the dome and flue gallery, there are two reasons for doing this. Firstly to isolate the gallery from the dome thereby reducing heat loss by conduction to a heavy flue gallery heat sink and secondly (IMO more importantly) it can act as a thermal expansion joint reducing the tendency for the hotter inner oven parts expanding and placing stress on the cooler gallery. However calcium silicate board is not particularly flexible so it won't perform this function particularly well. Some builders use ceramic blanket, sealed off with some high temperature flexible sealant. In my own build my design has a lightweight and therefore low thermal mass castable refractory gallery, insulated on the outside, with the expansion joint between it and the uninsulated outer decorative arch. I fill this gap 8-10mm with some vermicrete which is somewhat elastic.
I was looking at purchasing my materials from Consolidated Refractories in Greensborough. Research tells me to use fondue(proper mortar) (type of refractory mortar for joins bigger than 5mm). The section i put doors on wouldn't be for wood storage but rather cooking tools etc. I also plan on building a narrow roof to protect the entire cooking area including the new pizza oven.
I appreciate the tip re the CalSil board. Using the ceramic blanket to separate and insulate the dome from the gallery brings up the issue of how wide should it be and how wide a gap will the high temp silicone be able to bridge? I can rebate the first gallery brick to reduce the gap were silicone is needed but will this then effect the insulative effect? This would allow up to 40mm of blanket and a 10mm silicone section at the face of the same brick.
Funny you mention you are building a concrete table. Here is a photo of one I built last year. It has 4 sections which bolt together and weighs about 400kg in total. I just need to find some chairs to suit.
Fondu is the product name for Ciment Fondu which is a brand of calcium aluminate cement. It is not (to my knowledge) a mortar. I'm pretty sure you will need to add either sand or if you're really keen, a fine high temperature aggregate to it to make a refractory mortar. It will have a higher tolerance for heat than the mix most on this site have used which we refer to as "Homebrew". I use calcium aluminate cement for my ovens, but apart from being around 10x the price of portland cement it also comes with some problems. It has a very short working time so making up small batches is essential Depending on your weather conditions you may need to use chilled water because it is extremely temperature dependant. I live in the tropics and always have to use chilled water in the hotter (1/2 the year) months. Once it begins to harden it cannot be rewetted like portland cement mortars, it must be discarded. The benefit of this accelerated reaction is that because it achieves full strength so fast, castings can be de-moulded in 24 hrs and do not require extended damp curing, I give them 48hrs. Another disadvantage is that it picks up moisture from the atmosphere more easily than Portland and creates lumpy spoilage, again it should be discarded. bags should not be left open or stored on a concrete floor. Also if you use a super plasticiser in an effort to reduce water content or increase slump, be very careful because it is far more sensitive. ie about twice the normal effect it has on portland concretes or mortars. So use it very sparingly. I believe the manufacturers of refractory mortars recommend thin joints because they don't want warranty issues if steam spalling occurs. For thick joints, whether portland based mortars or calcium aluminate cement based, a fair measure of protection can be achieved by the addition of burn out fibres as already added to bagged premixed proprietary castable refractory products.
By contrast the Homebrew 3:1:1:1 mix has proved adequate as a mortar for ovens as well as a castable refractory for a cast dome, but not up to it for an oven floor which sees higher temperatures an much faster heat up times. Apart from being far cheaper, is much more user friendly, but does require extended damp curing to enhance strength.
Beautiful table.
Gecko245 I really like your table, especially the voids in the side supports! How did you make those?
Good to know about the different mortar options and their pro's and con's, thank you. How short is the working time for the Cal Al Cement? 10, 30 or 60 minutes?
For the table I made a 50mm thick form for each of the sections. I found some 50mm polystyrene and broke it up into rough shapes. I then placed the reo in position to mark where it sat on the polystyrene. Next I removed the reo and used a soldering iron to channel out lines for the reo to sit in the middle of the polystyrene and form. I used silicone to build over the reo, stopping the concrete from filling the void I had made. The reo was placed in position which held the polystyrene in place during the concrete pour. Once the concrete was set it was just a matter of knocking out the polystyrene, blowing out the remaining bits with my air compressor and peeling out the silicone.
As I mentioned it is highly temperature dependant, far more so than Portland cement mortars. As an example some folk I was advising here about its use found it had gone off before they could even place it. They gave up and went with the homebrew mortar. We live in the tropics and our air temp is regularly in the mid 30s C and tap water around 30C. During our hot months (1/2 the year) I always use chilled water which gives me enough working time to place around 12L of wet material comfortably at a time.Citric acid works as a retarder, but I've not tried it.
Seems like the calcium aluminate cement is the better option although being harder to work with. I think I'll try it first, safe in the knowledge there is a second, easier option which also seems to work quite well. I'll have a bit of a chat to the guys at Consolidated Refractories also.
I appreciate you sharing some of your wisdom.
Thank you.
I've made a start on my oven and will post all the photos and info in the brick oven photo gallery section.
I'm looking at pouring my suspended slab within the next month and am happy to upload my progress pictures for you all to critique.
Thank you in advance.
Dragan
Hi Dragan,
what size internal diameter are you planning?
Also, is it to be a brick build or cast?
Dave
Hi David,
I'm planning on having an internal diameter of 900mm and will be using refractory bricks for the dome. Originally I was thinking about cutting every brick to minimize internal and external gaps but after much research it seems the effort to do that may not be of great benefit so I will simply concentrate on making the internal joins small.
Decisions on the amount of cutting to do can often depend on whether you buy a wet saw or rent one. If you buy you can cut bricks at your leisure, making the required angles as the build progresses, but if you rent you’ll probably cut all your bricks in half and adjust the mortar gaps as you build.
Contrary to most builders here who aim for tight and precise joints, the famous kiln builder Daniel Rhodes, the author of Kilns, generally regarded as the kiln builders bible, he states,
"In kiln building it is much better to have a loose structure than a tight one. For this reason the amateur may have a slight advantage over the professional mason. Because his bricklaying is apt to be somewhat loose and not tightly locked together I have seen kilns made by professional bricklayers which in use suffered severe cracking and swelling due to the overly tight and precise workmanship and lack of expansion joints."
We're not building kilns here and our ovens only experience about half the thermal expansion of a kiln, however the same principles apply.
Interesting! I think I'll cut my side angles and fill under the back of each row with the proper mortar, thank you. What are your thoughts regarding the 25mm CalSil board placed between the dome and the gallery arch?
Here is a photo of what I have built so far. I precast my own 50mm concrete top which are still to be polished a little. Under top storage for wood, charcoal etc. I might end up putting a couple of doors to close in one section in the future. The pizza oven will go in the corner section once I've poured my slab.
I'm not sure what you mean by "proper mortar", but most of the proprietary refractory mortars recommend very thin mortar joints, which would be contrary to filling the outside gaps, as well as going through a lot of expensive mortar.
Your set up looks great, I'm doing a polished concrete table beside my oven at the moment, it's messy and painstaking work and hard to know when to stop.
Putting doors on the wood storage area will make things look pretty, but has the unfortunate result in keeping the wood damp, especially in an uncovered outdoor area.
Regarding the calsil between the dome and flue gallery, there are two reasons for doing this. Firstly to isolate the gallery from the dome thereby reducing heat loss by conduction to a heavy flue gallery heat sink and secondly (IMO more importantly) it can act as a thermal expansion joint reducing the tendency for the hotter inner oven parts expanding and placing stress on the cooler gallery. However calcium silicate board is not particularly flexible so it won't perform this function particularly well. Some builders use ceramic blanket, sealed off with some high temperature flexible sealant. In my own build my design has a lightweight and therefore low thermal mass castable refractory gallery, insulated on the outside, with the expansion joint between it and the uninsulated outer decorative arch. I fill this gap 8-10mm with some vermicrete which is somewhat elastic.
I was looking at purchasing my materials from Consolidated Refractories in Greensborough. Research tells me to use fondue(proper mortar) (type of refractory mortar for joins bigger than 5mm). The section i put doors on wouldn't be for wood storage but rather cooking tools etc. I also plan on building a narrow roof to protect the entire cooking area including the new pizza oven.
I appreciate the tip re the CalSil board. Using the ceramic blanket to separate and insulate the dome from the gallery brings up the issue of how wide should it be and how wide a gap will the high temp silicone be able to bridge? I can rebate the first gallery brick to reduce the gap were silicone is needed but will this then effect the insulative effect? This would allow up to 40mm of blanket and a 10mm silicone section at the face of the same brick.
Funny you mention you are building a concrete table. Here is a photo of one I built last year. It has 4 sections which bolt together and weighs about 400kg in total. I just need to find some chairs to suit.
Fondu is the product name for Ciment Fondu which is a brand of calcium aluminate cement. It is not (to my knowledge) a mortar. I'm pretty sure you will need to add either sand or if you're really keen, a fine high temperature aggregate to it to make a refractory mortar. It will have a higher tolerance for heat than the mix most on this site have used which we refer to as "Homebrew". I use calcium aluminate cement for my ovens, but apart from being around 10x the price of portland cement it also comes with some problems. It has a very short working time so making up small batches is essential Depending on your weather conditions you may need to use chilled water because it is extremely temperature dependant. I live in the tropics and always have to use chilled water in the hotter (1/2 the year) months. Once it begins to harden it cannot be rewetted like portland cement mortars, it must be discarded. The benefit of this accelerated reaction is that because it achieves full strength so fast, castings can be de-moulded in 24 hrs and do not require extended damp curing, I give them 48hrs. Another disadvantage is that it picks up moisture from the atmosphere more easily than Portland and creates lumpy spoilage, again it should be discarded. bags should not be left open or stored on a concrete floor. Also if you use a super plasticiser in an effort to reduce water content or increase slump, be very careful because it is far more sensitive. ie about twice the normal effect it has on portland concretes or mortars. So use it very sparingly. I believe the manufacturers of refractory mortars recommend thin joints because they don't want warranty issues if steam spalling occurs. For thick joints, whether portland based mortars or calcium aluminate cement based, a fair measure of protection can be achieved by the addition of burn out fibres as already added to bagged premixed proprietary castable refractory products.
By contrast the Homebrew 3:1:1:1 mix has proved adequate as a mortar for ovens as well as a castable refractory for a cast dome, but not up to it for an oven floor which sees higher temperatures an much faster heat up times. Apart from being far cheaper, is much more user friendly, but does require extended damp curing to enhance strength.
Beautiful table.
Gecko245 I really like your table, especially the voids in the side supports! How did you make those?
Good to know about the different mortar options and their pro's and con's, thank you. How short is the working time for the Cal Al Cement? 10, 30 or 60 minutes?
For the table I made a 50mm thick form for each of the sections. I found some 50mm polystyrene and broke it up into rough shapes. I then placed the reo in position to mark where it sat on the polystyrene. Next I removed the reo and used a soldering iron to channel out lines for the reo to sit in the middle of the polystyrene and form. I used silicone to build over the reo, stopping the concrete from filling the void I had made. The reo was placed in position which held the polystyrene in place during the concrete pour. Once the concrete was set it was just a matter of knocking out the polystyrene, blowing out the remaining bits with my air compressor and peeling out the silicone.
Originally posted by Gecko245
Seems like the calcium aluminate cement is the better option although being harder to work with. I think I'll try it first, safe in the knowledge there is a second, easier option which also seems to work quite well. I'll have a bit of a chat to the guys at Consolidated Refractories also.
I appreciate you sharing some of your wisdom.
Thank you.
I've made a start on my oven and will post all the photos and info in the brick oven photo gallery section.
Attached Files