31"/800mm in Eindhoven, the Netherlands: Design critique and build topic

[nlinva]

Yes, that Permatex stuff is quite sticky and hard to get on smoothly, especially in a narrow, hard-to-reach crack. I had the same problems you did, and mine looks quite messy; I might try to clean it up a bit, but as you say, it's really not going to matter much. I did learn my lesson and use tape for the silicone gasket between the front landing and the arch landing inside the vent arch. That worked very nicely.

I did actually try to tape where I put the Permatex Red, but the masking tape I had was not sticking to the firebrick surface. If I had to do it again (if I ever build another oven), I would make sure to get tape that sticks well.

[Toiletman]

Forgot the pictures

[Toiletman]

After enjoying a small holiday I did manage to do a little work on the oven: I've added the fire-rope + kit on the back of the gallery and the permatex kit on the inside. The latter was challenging: the small gap doesn't allow the 'spout' to go into it deeply, so the process was rather messy. I should've taped it off beforehand to prevent the mess, as with the granite, but I found out while I had the kit open already, so I figured it might dry out and that I should clean up mechanically afterwards.
This turned out to be only partially possible, but in the end, as already mentioned it's all going to be mostly covered in soot, so I decided not to be too perfectionistic on it .
I took some final measurements of the chimney connection and covered the oven for winter. Although the weather has been really nice the last days I will only be able to do significant work after having the chimney connection on, and I don't think it's realistic I finish that before the weather will turn worse.

You do have a pretty wide opening in the vent. Since the bricks on the left and right edge are not quite vertical, it looks like it becomes even wider beyond the initial opening. I think that's common, but am not sure how it affects air flow. It could be a plus, as a place for smoke to collect rather than coming out the front, but it could also mean that air slows down before speeding up again, which might affect the draw. Or maybe these thoughts just show my complete ignorance in these matters :-)

You are right about this, although I'm not sure how much pressure loss will result from it. It might be in the similar order of magnitude as the improvement by rounding the corners. Anyway, by the time I'm making smoke it might be a fun area to investigate to see if the smoke indeed does 'recirculate' in the expansion chamber.

[nlinva]

Ha, the "before cleaning" picture of the vent arch does make me feel a little better about my brickwork, though sadly my "after cleaning" is still closer to your "before cleaning" :-).

You do have a pretty wide opening in the vent. Since the bricks on the left and right edge are not quite vertical, it looks like it becomes even wider beyond the initial opening. I think that's common, but am not sure how it affects air flow. It could be a plus, as a place for smoke to collect rather than coming out the front, but it could also mean that air slows down before speeding up again, which might affect the draw. Or maybe these thoughts just show my complete ignorance in these matters :-)

[UtahBeehiver]

You are correct on the vent cross sectional should be larger than the chimney cross sectional area. FYI, a rectangular opening is not as efficient as a circular cross section so it is good you vent cross section is larger in area than the chimney.

[Toiletman]

Thanks for the support gents!

RandyJ The curing fires are going to be in spring. It's getting pretty wet here now in Autumn and I don't see much sense in trying to keep half-fitting blankets dry in that weather. I'll use the winter to cast a gallery-->chimney connection and then be ready to fit it and insulate the oven in spring... and then finally pizza time hopefully!

Looking good!! And glad to hear it remains standing! Your brickwork continues to be so impeccably clean, I'm kind of embarrassed to upload pictures of mine :-)

I built my vent arch last weekend, but have kept the form under it until I add some buttressing. That should happen this weekend at the latest. The flue hole in my arch is a lot smaller than yours (starting opening is about 10" x 7"), but should still be plenty large for its purpose, I hope.

You're only seeing the 'after cleaning' pictures now. I've attached some for during the building process and after removal of the form. Much less clean! With the dome arch I waited 24h before removing the form, after which it was much harder to clean the inside. This time it went a lot easier with more fresh mortar after 6-8hrs. I hope yours is going to be fine too!
In the end UtahBeehiver is right of course: it's all going to get black, so no one is going to notice anyway

With respect to the vent opening: as long as it's larger than the chimney cross sectional area it should be OK. Mine might actually be too big, but I wanted to capture also a significant width of the barbecue area to ensure the smoke will also go in. Now I'll have to make a bigger/higher transition piece not to get the angles too flat.

[UtahBeehiver]

Nice and clean, don't be disappointed when you start curing your oven that it will load up with carbon, it is just part of the process.

[nlinva]

Looking good!! And glad to hear it remains standing! Your brickwork continues to be so impeccably clean, I'm kind of embarrassed to upload pictures of mine :-)

I built my vent arch last weekend, but have kept the form under it until I add some buttressing. That should happen this weekend at the latest. The flue hole in my arch is a lot smaller than yours (starting opening is about 10" x 7"), but should still be plenty large for its purpose, I hope.

[RandyJ]

Hey Toiletman congratulations on getting the entry arch finished. That is a big achievement. It is looking great. How log till you can start your curring fire's.

Randy

[Toiletman]

Took the form out and .... it stands! (sorry for the crappy picture quality, my phone doesn't do dark very well).

The rear stones around the keystones seem a little too lean, but so far it's self supporting and I cleaned it up. Might add a little bit more mortar tomorrow to those lean stones or save it for after the holiday.

[Toiletman]

The diagonal cuts in the sleeve provide secure adhesion to the gallery, not for any venting purpose. I surround the sleeve with some dense castable about 100m highto cover them the sleeve not being a full circle allows for it to have some expansion relief.

I just catered for a function last night. Here are some pics with flue in and out before lighting. We affectionately call him Augustus Gloop.

Thanks for the further clarification david s . Great design: both technically as well as a fun aesthetic!

I've been again moving at a glacial pace, but today was a great milestone: the chimney arch is in! It's still supported by the form, so I'll take it out tonight to clean-up the inside (it's a mess) and hopefully will still have a standing arch after that.

See the pictures and below explanation for some further details:

• It was necessary to cut another brick in the sidewall diagonally so properly support the arch and accomodate the height of the sidewalls due to the extra high joints. This became quite ugly and will probably become a very thick joint as the actual arch became once again higher.
• I worked with quite wet mortar again, like with the dome arch, but this time my form was not closed, but open. This led to quite some mortar droop. I hope some of the vertical joints didn't loose their complete mortar, because then of course I'll have a collapse on my hands tonight.
• Getting the bricks and joints to look nice was quite some work, but with a lot of wedges and proper marking it went in quite well today
• The thermal gap will need its cord and kit still. This should be fine, but it was quite some work to get it cut correctly and hopefully I managed to keep it clean of mortar. For the people that fitted these cords and kit while mortaring in the bricks: how did you do that? doesn't it become a crazy mess with all the mortar joints?

[david s]

The diagonal cuts in the sleeve provide secure adhesion to the gallery, not for any venting purpose. I surround the sleeve with some dense castable about 100m highto cover them the sleeve not being a full circle allows for it to have some expansion relief.

I just catered for a function last night. Here are some pics with flue in and out before lighting. We affectionately call him Augustus Gloop.

[Toiletman]

Your assumptions about my drawing are all correct. Not totally sure about your drawing, but I think you get the idea. You do have a rather sharp angle for the smoke to make into the gallery, but I'm sure it will work ok as shown. Because vermicrete is relatively weak, I use about a 6:1 mix there which provides enough stability for the base of the flue pipe at the same time as providing enough give. Yes I do allow a slightly loose fit between the pipe and the flue gallery collar.

Thanks for your input and pics david s , that's extremely helpful. It also seems that you have got the cost optimization down to an art .

Since today is a rainy day I can't continue on the arch form, so instead I'm exploring the possible flume mold a little bit more. You were spot on with your judgement of the angles: I've attached a pic of the smoke channel (the actual casted material will go around), and it shows the angle is about 30 degrees. I'll try raising the chimney to make it 45 and see how that looks.

Regarding a sleeve for removable flue which I have done for all mobile ovens as well as a number of fully completed builds that require long travel distances, I/ve added some pics which should tell the story of how I do it. The little tags on the end of the sleeve prevent the pipe from going too deep into the sleeve.

The first pic of the sleeve is of course upside down.Second pic shows some plasti wrapped around the pipe to prevent the castable from sticking to the pipe and makes removal easier. Of course it is then discarded allowing a nice smooth fit.

Having done this many times it is not as laborious as it looks and it's now not too much more trouble than doing it the usual non-removable way.

Regarding punching holes in the pipe, I’d strongly suggest you don’t try that. Although the stainless is thin (0.5 mm) it’s very strong and you’ll distort the pipe way too much, especially as you intend making it slide nicely in a sleeve. Far better to drill holes. But be sure to use slow speed lots of pressure. Start with about 3.5 mm the enlarge to 6mm. About 6 should be enough to allow some stem to pass to relieve pressure but not enough to distort the pipe

Trying to make sense of your picture, so please bear with me with some additional questions: you have used a thin sheet metal sheet to form the collar to connect the removeable pipe to the oven. That collar will stay permanently attached to the oven?
In this collar you manufactured tabs for the pipe to rest in, and with the initial plastic you ensure a nice snug fit. I'm assuming the diagonal cuts you made are the 'vent holes' to allow steam to escape from the insulation into the chimney?

Good tips to for drilling holes, for some other stainless work I spent some time until I found the right type of drills, but I now have 'em. With the adapter I had in mind the pipe would be far above the holes, but your solution seems much more cost effective, and also uses materials that can be sourced right around the corner.
Do you have any experience with condensation rolling down the chimney finding its way into the vermicrete? I was thinking it could be solved by adding some beads of high temperature kit on the outside (see picture).

[david s]

Your assumptions about my drawing are all correct. Not totally sure about your drawing, but I think you get the idea. You do have a rather sharp angle for the smoke to make into the gallery, but I'm sure it will work ok as shown. Because vermicrete is relatively weak, I use about a 6:1 mix there which provides enough stability for the base of the flue pipe at the same time as providing enough give. Yes I do allow a slightly loose fit between the pipe and the flue gallery collar.

Regarding a sleeve for removable flue which I have done for all mobile ovens as well as a number of fully completed builds that require long travel distances, I/ve added some pics which should tell the story of how I do it. The little tags on the end of the sleeve prevent the pipe from going too deep into the sleeve.

The first pic of the sleeve is of course upside down.Second pic shows some plasti wrapped around the pipe to prevent the castable from sticking to the pipe and makes removal easier. Of course it is then discarded allowing a nice smooth fit.

Having done this many times it is not as laborious as it looks and it's now not too much more trouble than doing it the usual non-removable way.

Regarding punching holes in the pipe, I’d strongly suggest you don’t try that. Although the stainless is thin (0.5 mm) it’s very strong and you’ll distort the pipe way too much, especially as you intend making it slide nicely in a sleeve. Far better to drill holes. But be sure to use slow speed lots of pressure. Start with about 3.5 mm the enlarge to 6mm. About 6 should be enough to allow some stem to pass to relieve pressure but not enough to distort the pipe

[Toiletman]

A very belated response to your question about the chimney anchor plate (post #39). I'm now also at the stage of working with that too. I went ahead and bought the (indeed quite expensive) anchor plate for the vent system I am using. It is much too large, so I'm cutting it down a bit. Moreover, in retrospect perhaps I didn't even really need it.
david s offered some ideas about how to go without a plate altogether at post #75 on my build; the link he provided is https://community.fornobravo.com/for...ery#post446435 (hope that works).

That's an interesting suggestion. I think he posted it already here also, but I didn't fully grasp it at the time. Let me reproduce the sketch below, together with the proposed version for my oven. Some questions on the design david s :

• I'm assuming there's a gap in diameter between the gallery and the bottom of the flue, but the vermicrete is tight up to it? The slightly flexible vermicrete/blanket allows thermal expansion? Do you use a coarse type of vermiculite there? Mine is pretty fine, I would expect it to be expanded to dust after a while?
• You seem to add blanket and vermicrete in the cross section of the flue, do you do that full-round? basically adding a 'bump' around the flue? From your pictures that seems to be the case.
• Have you made any designs with removable chimneys?

As the oven should live under a tarp during the wet winters I plan on using a removable chimney. Due to possibly building a pergola I bought double walled chimney pipe. The adaptor to fit that is also double walled so the outer diameter of it will probably expand significantly less. Even so I'll apply the permatex around it, to make a good elastic seal against moisture ingress.

See attached sketch for the rough idea. I'm also considering punching holes in the inner pipe, such that steam inside of the vermicrete can escape. However, see below for some further thoughts on this.

As for condensation -- I think in general the problem is that rain & damp can enter unless you apply some kind of flexible silicone gasket connecting the outer cover of the oven to the chimney pipe. Normal stucco or render might not be flexible enough to handle the pipe's tendency to expand. My current plan is to take a terracotta flowerpot and saw off the bottom to make a collar, and connect the collar to the chimney pipe with high temp silicone. The flowerpot will sit on insulation (so its bottom will not directly touch either brick or anchor plate), and can also be filled with insulation to reduce possible temperature shocks it might be exposed to.

From the documentation that I've seen on the 'condensation' connections on chimney pipes, their story is mainly about the moisture in the fumes condensing. Either due to cold pipes, or after firing. This then drips down into any dead-ends, which you typically have when connecting a stove/furnace type of apparatus. As we don't have dead ends and fire at quite high temperatures I'm not too worried about this problem. Worst case you have some drops falling onto the floor tiles in your gallery, but that's not a place where you should be too worried about a little bit of moisture (assumption).
The only worry I have is in punching some holes in the inner pipe to allow steam to escape from the vermicrete/blanket: this would also be a great way in for any drops of condensation rolling down the inner pipe.
As to rain or moisture rolling down the outer pipe and creeping into the gap I plan on using a similar approach as you and others are doing with terracotta disks and flexible seals. This should prevent any direct ingress.

PS: status update on the oven:

• Gallery arch stones have been cut to size, cutouts for the gap between inner and outer arch still to be cut by grinder
• Cleaned out the wet saw and put it inside to prepare for the 'wet and cold' season. The cuttings had some nice layerings due to cutting light firebrick, red brick and granite :-D
• Currently building the gallery arch mold. Hope to finish it on wednesday and maybe put in the arch in the weekend
• Seriously considering casting the arch to chimney connection: would allow me to do this inside during the winter, make a much nicer shape to increase draw and save a lot of weight on top of the arch. As you also mention nlinva I was a little bit too proactive in ordering materials and now find out that I missed some chimney parts and might end up paying double shipping costs in the end anyway...