2 questions to start!

[pepe]

Hello wise ones! I am very happy to be joining the forum, if I recall correctly, I have meant to do so since 2016. I have 2 questions to start my 36 inch WFO:

1. I am having a lot of trouble finding if the homebrew is still 3:1:1:1 or 6:1:1:1, I get mixed results with the search function.
2. I have very little money so I am making my oven completely out of 4x10x20 (cm) red-clay bricks (100% clay) for about 70 USD I get 200 bricks. I am planning on having the first row standing up and have some sort of a ball for form for the dome. Given the option I prefer not tapering bricks, is it possible to make the dome without tapering?

Thank you very much for your input!

[Gulf]

Hi Pepe,

Welcome to the forum. I hope one of the "wise ones" will respond. But, I will give my opinions to your questions.

I don't know where you are finding the "6:1:1:1" recommendations? The home brew that we recommend is 3:1:1:1. To be exact, it is 3 parts sand, 1 part portland cement, 1 part hydrated lime, and 1 part clay.

For brick construction, I recommend the IT . You will find many examples of the IT on this site. You mentioned standing the first row upright. That is called a "soldier course." That is kind of old school from the days before the IT. The It makes the laying of a hemispherical dome much easier. Soldier courses require that the sides of the dome to be buttressed.

Yes, you can build the dome without tapering the brick. We like to say "mortar is your friend". If it is home brew, you can use it liberally.

I hope that the 100% red clay bricks are solid with no holes. If not, you need to reconsider.

There is another option that is open for you to consider. That is a home brew castable. Many, who find the firebrick too expensive or not obtainable have chosen this option.

[pepe]

Thank you very much for your response Gulf I was digging for the 3:1:1:1 formula and constantly found users bring up a 6:1:1:1, in one particular thread they talked about adding some sort of hair sized needles of some sort, It is very overwhelming for someone with absolutely no hands on construction experience. Is this mix water proof or outside proof? I would like to leave as an igloo shape for some time before I can save for a ceramic blanket.

I actually devised a metal ring that will enclose the first row of my dome holding them together, and i will form it on the floor with help of a form and when finished I will be able to carry it with help and install it on the soldier course, so maybe the buttressing can be lighter?

They are solid 100% red clay bricks extruded and fired up to 1000 c so I think they are ok.

I have thought of casting but I am so exited to try and have an actual brick oven... But it is a great idea that I know I will someday end up trying as well.

Oh and BTW, looking at your build, I would certainly say that you are definitely one of the wise ones!

[Yokosuka dweller]

Hi Pepe, I'm always reminded by my wife that I'm not a 'wise' one. Also, just a beginner here, but having gone through most of my own build by now I will chime in:

Homebrew is 3:1:1:1, by volume and not by weight, although you're right that there has been discussions on here whether this mix should be different and leaner to retain some plasticity/expansion. I mixed it by volume and some times, if the mix was too rich or too wet I added sand - fine silica sand is good, masons sand should be fine also.

I personally would not to a first course of standing bricks. I don't see the advantage in doing so, better to place bricks laying down on or outside the oven floor. But if you've already devised a metal construction to buttress then maybe okay, but that metal should not rust, or if it expands differently than the bricks in a hot environment you're adding a variable to the mix that may cause cracking later on. Also a course of standing bricks often creates a lot of vertical mortar gaps which then become difficult to bridge on subsequent courses without the mortar gaps lining up-something to keep in mind...

Firebricks draw water, I do not know how red clay bricks work in that regard, but an uninsulated dome open to weather would get wet, unless you cover it up with something. On this forum the opinion is also that if you fire an uninsulated oven the temp difference between internal face and external face of the bricks can be so great that it causes cracking. But read up on it and see.

Instead of the pricey insulation wool, others have used mix of 10:1 perlite/concrete or vermiculite with success, several inches though so that would have to be in your plan and space added to your hearth stand. Even such a insulating layer is not water resistant on its own but would have to gradually dry and then be covered with stucco or another water tight layer/stucco. If you like the bricks look, which I do think looks great, then some people have added an external layer of normal house bricks, even thinner pieces to get to that look after insulation. But that is of course a lot of work to do.

Hope this helps.

[pepe]

Yokosuka dweller thank you for your response, It does not look like you are a noob at all

Thanks for the info that homebrew formula is by volume, that would have been a big miss from my part. For dome insulation I am for sure going 10 parts perlite 1 part concrete, I am just not sure if the perlite I have is the right one, they are small sized white stones that can be crushed to powder (sold in hube potato bags at the nursery). Should you fire the oven first let dry and then add the vermicrete?


For floor insulation I am going HEBEL/AAC because it is so cheap here.

Will search for a nice stucco, or maybe something we call Yesso that in theory does not crack.

Thanks!

[Gulf]

......in one particular thread they talked about adding some sort of hair sized needles of some sort, It is very overwhelming for someone with absolutely no hands on construction experience....

That was most probably a reference to a home brew castable formula. You definately don't want to add the needles to the home brew mortar.

....Is this mix water proof or outside proof? I would like to leave as an igloo shape for some time before I can save for a ceramic blanket.....

No, but In that case (If not a permanent one) I would build a tempoarary shed over the build.

I agree that masonry sand will be ok. But, I would sieve it through an old window screen to remove the larger aggreagate. Some of the larger aggregate in masonry and all purpose sand is small rocks.

[Yokosuka dweller]

Small mistake from my side - perlcrete/vermicrete is not mixed 10:1 with concrete, but 10:1 with normal portland cement. Perlite comes in fine, medium, or rough sizes, I worked with medium size pellets (popcorn glass?), dry mixing by hand, adding a scoop of clay to make it easier to apply. Where I live the perlite from nurseries is in small bags and expensive, but you can get 50L bags at the local home improvement store.

I don't think you should fire the oven before adding insulation, but after - however this is an ongoing discussion and people have done different things. There is an elaborate 'curing process' mentioned elsewhere you can see what steps reduce risk of oven cracking once you're ready to fire it.

[pepe]

Yokosuka dweller I have had a couple of sleepless nights thinking of what you said, I have decided going without the metal forms but i really like the look of having the first set of briks "upright". Would this be safe or is it the same as using a soldier row?

[Yokosuka dweller]

I can't really see the detail of the photo but I guess this is half 'soldiers' as first course? If you do that, the advantage will be that there won't be a horizontal mortar joint right at your floor which a peel can get stuck in. Also, yes the force pushing outwards from the dome will be closer to the floor and thus, seemingly less of an issue. But depending on the shape of your oven entry/internal arch and external arch, and how you tie it in, it would probably still be better with buttressing. Read up on that, I don't know enough, but such buttressing can be done with an extra course of bricks on concrete external to the arch bricks. There are many examples on how this can done. And this will also depend on whether your oven entry arches will be hemispherical or have vertical parts, the former more inherent strength.

I have a friend who did this (half soldiers first course), and he seems to be fine with that - no problems. So you could so it. I guess you would still run into some challenge with avoiding vertical mortar joints lining up between first and second course.

One other thing to consider now is whether you build your dome outside or on the oven floor? Building it outside makes it easier to replace potentially broken bricks later on compared to if you place your dome on top of the oven floor. If you place external to the oven floor, which is what I did, remember to keep a half cm gap between floor and first course to allow for expansion. Just put some cardboard between floor and dome course that will later just burn off to keep the distance gap. Also, do not mortar oven floor to the hearth, let it float on sand or dry clay for level. I didn't put anything, my hearth was already level. Same with first course let it 'float' and mortar only between the bricks, not under them.

That all being said, hope someone else who's built with half soldiers can chime in.

[pepe]

You are correct Yokosuka dweller what I posted is in fact a half soldiers course. I am placing the oven over a metal rigid stand in hopes of lowering the overall weight. I honestly have little masonry skills but I am a fast learner. I was going full soldier because the pompeii oven plans have that as an example, I do not remember buttressing being mentioned near that particular step.

I plan to set either AAC or a 4 inch 5:1 percrete subfloor on top of the metal table, on top of that, two stacks of bricks and sand in between face down as my cooking surface (to have the same 10 cm of depth as the walls), and lay the first half soldier on top of my cooking floor, I know I wont have the skill to cut them into a nice even circle. Do you know if smoothing the exterior with the homebrew mortar and adding a few inches of the 10:1 percrete as insulation work as enough "buttress"?

BTW sorry for my noobness, I know I must sound like an absolute wanker!

[Yokosuka dweller]

You don't sound like a wanker at all. Myself had to try various ways to find the right answers during my build, and still am.... Thing is, many of the questions have been asked here before numerous times, so some of the old timers on here sometimes seem a bit reluctant to repeat the same things. So as relative newbies here I guess we also should carry the info forward but careful not to share wrong info. So no worries at all. Can only say that some times when you don't get the answers you need it's better (but slower) to trawl through past posts yourself, I had to do that and that's how I learned there are many ways to Rome.

My opinions, you know...if metal rigid stand, make sure it's really rigid and strong enough and can withstand over time. These ovens can weigh in excess of 1-3 tonnes (with stand and foundation etc) so it's really not a lightweight operation.

The pompeii oven plans are a good place to start, but honestly, they are also a bit outdated. For example techniques to interlock oven arch with dome by tapering the bricks is the norm to do now, not included in the manual, serpentine arch, and many other innovative improvements over the years. Someone should update the plans/make a 2nd edition. As it is now, the forum is a treasure trove, but gotto dig...

Your oven floor will be two layers of bricks on top of the p-crete (at least 4", more is better) ? That will increase the heat sink and takes longer to heat up the floor but then also retains heat longer I guess. Why two layers? Also consider drilling/forming a couple of meshed 'weep holes' in the floor of the hearth so any water can drain out from under the insulation. I cut oven floor inside dome walls with 10cm regular angle grinder (masonry blade) and a chisel. Once you scribe the diameter on the bricks that wasn't very difficult to cut, just dry run the bricks uncut first to get a pattern you like (herringbone is one option), and where the edge cuts are easy.

About buttressing: P-crete doesn't have much structural strength so would probably not be enough as buttressing. Also, I think buttressing is not the main issue for the dome but for the matching arch later on which will carry weight of flue. But pls try to ask someone with ample experience, such as UtahBeehiver he would know...

[pepe]

Your oven floor will be two layers of bricks on top of the p-crete (at least 4", more is better) ? That will increase the heat sink and takes longer to heat up the floor but then also retains heat longer I guess. Why two layers? Also consider drilling/forming a couple of meshed 'weep holes' in the floor of the hearth so any water can drain out from under the insulation. I cut oven floor inside dome walls with 10cm regular angle grinder (masonry blade) and a chisel. Once you scribe the diameter on the bricks that wasn't very difficult to cut, just dry run the bricks uncut first to get a pattern you like (herringbone is one option), and where the edge cuts are easy. UtahBeehiver he would know...

Thank you for all of your sound advice, I thought of using to rows of bricks for more mass, but maybe I can just use tiles or more sand and fireclay? I am aiming for an even 10 cm thick dome and floor depth. I have been looking for examples of the weep holes with no luck, do you have any pictures of yours? I would like to incorporate that. Right now I am doing my shopping list and am not sure if 135 lb of sand, 45 lb cement, 45 lb lime, 45 lb fireclay is too much material for my mortar. It is sort of an average I have found on threads but it seems to be too excessive, I mean that´s almost half the brick dome weight!

[Yokosuka dweller]

I used maybe around 50-60kg sand, 10-15kg lime and same amount of fireclay for my 31" oven, so you're not far off I guess. I also used quite a bit of fireclay from the powder produced from cutting the bricks, which essentially is fireclay and can be used as long as you remove the small pieces of brick in it. As for cement maybe I used around 20kg for the brick part of the build. Looking at it now, I guess my homebrew was not exactly 3:1:1:1, but I also use a rather aggressive hydraulic lime and a relatively liberal estimate by eye method adding sand if it was too wet etc. It will be alright, cracks or not...In the end of the day I think the amount varies depending on how much mortar you use to glue the bricks. Some people do more cutting to fit the bricks more accurately with smaller mortar gaps on the inside of the oven, and others use more mortar, not worrying too much about gaps. Whatever works best for you. I've also read that due to heat expansion of the oven dome, it's very likely that cracks will form at some point, and you will want to have mortar as the first weakest point of cracking rather than having a brick crack, so a few thicker joints per course with some mortar even in the interior joint may be better than a completely dry jointed oven that has no expansion space between the bricks. If you do that the you can place a thicker joint towards the oven opening as nobody will ever see that once the oven is done. More importantly just make sure to try to avoid stacking the joints between courses as much as possible (gets more difficult as you move up).

For floor, you can use two rows of bricks for more mass under the oven, I think will enable you to hold more heat for longer periods of baking/using the oven if that's what you want. Some people have, as far as I've read on here, laid their floor bricks with 'rowlock' upwards to create more mass. Tiles? Not sure about that, it has to be something that is designed to take a lot of heat.

I was looking through my photos for weephole, but seems I didn't take any photos so just used the advice that's been mentioned on here and interpreted it on my own. I'm not sure if I did it right, but had a 12mm (1/2") concrete drill bit and drilled two holes through the green concrete and then glued some mosquito ned mesh to the top and bottom. I also used angle grinder to grind a slight concave around the weephole so water would not be stopped by the slight edge created by the glued on net.

Making a couple of weepholes were important in my case, since my perlcrete insulation is in a cast pool. If you don't use that method but place the insulation on top of the hearth stand (in stead of in it), then maybe such holes are less important. I guess the purpose is to allow any water that may pool under the oven a way to easily exit, should your oven get wet. It's also more important with weep holes if you insulate your oven floor with p/v-crete than with a ready made dry form of insulation (insblock or something else that's solid), since the p/v-crete takes a whole lot of water to mix and that needs to have an exit route.

[R3CALL]

pepe how did you get on, do you have any pictures on your cast as I am at this stage and need some inspiration?

[pepe]

pepe how did you get on, do you have any pictures on your cast as I am at this stage and need some inspiration?

Hi R3CALL , I will try to post some pictures tomorrow, I went all bricks, I only made a cast for the perlcrete insulation subfloor, I am actually having trouble with the mortar, I cant get it to stick to the second brick (any wetter and the mortar becomes pure liquid lol), I read I shouldnt wet bricks on the forum, but maybe my climate is too dry and so are the bricks. I am still searching and asking around, not sure what to do. If i find nothing I will have to make a few tests and see what happens (it is my first time using anything related to building).