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

[nlinva]

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).

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.

[Toiletman]

A small update:

In between the rainstorms today I've managed to cut the diagonal topping bricks of the gallery. It was quite some intricate cutting, trying to stagger in the buttress as well. I also found out that the walls have become slightly too high, so I'll have to chop a bit off the already laid bricks... otherwise the arch won't close off the dome arch. Ah well, you live and learn... I hope I'll be able to put in some decent cuts and not ruin the nice look of the gallery so far.

[Toiletman]

Toiletman the build is coming along very nicely. It won't be long and you will be cooking too. My son wanted pizza to celebrate the last day of summer before he went back to school. So I made pizza again and now have mad 46 pizza in this oven. Hopefully I can hammer out the rest of my pavilion now that I am not working 60hrs a week and very stressed out.

Randy

Wow man, you've been baking! I'm working on the diagonally cut bricks for the sides of the gallery... then it's time for the arch. Hope to finish it before it really starts getting wet and cold. Curing fires and baking is probably going to be next season.

[RandyJ]

Toiletman the build is coming along very nicely. It won't be long and you will be cooking too. My son wanted pizza to celebrate the last day of summer before he went back to school. So I made pizza again and now have mad 46 pizza in this oven. Hopefully I can hammer out the rest of my pavilion now that I am not working 60hrs a week and very stressed out.

Randy

[Toiletman]

Your granite front landing looks great! I have something similar planned for my oven, but in slate (and also with a simpler right angle joint -- I don't think I can do 45 degrees accurately enough :-)

As for the high temp silicon, Permatex's own website suggest that for even higher temperatures than the Permatex Ultra, you can use Permatex Optimum Red. Maybe worth a look.

For the rope, are you planning to put it right in the corner, or on the face of the arch, or on the side/top? I'm trying to think through what the pluses/minuses are of those options. On the face seems most straightforward, but on the side/top might make it less likely to get rope fraying accidentally enter the landing space, even if the silicon gasket fails. Not sure it would make a real difference, though.

Thx for the compliments and tips. I had the copper variant already on order, so I'll have to do with it.

I'm planning on having the rope on the side/top and the gasket on the face. Like you said: sealing on the sensitive side, and having the risky part the furthest away as possible, close to where the other nasty fibres are going to be (insulation blanket).

[david s]

Your granite front landing looks great! I have something similar planned for my oven, but in slate (and also with a simpler right angle joint -- I don't think I can do 45 degrees accurately enough :-)

As for the high temp silicon, Permatex's own website suggest that for even higher temperatures than the Permatex Ultra, you can use Permatex Optimum Red. Maybe worth a look.

For the rope, are you planning to put it right in the corner, or on the face of the arch, or on the side/top? I'm trying to think through what the pluses/minuses are of those options. On the face seems most straightforward, but on the side/top might make it less likely to get rope fraying accidentally enter the landing space, even if the silicon gasket fails. Not sure it would make a real difference, though.

You are right, the Permatex Optimum red is higher rated than the Ultra Copper. I've not seen it before, it must be a relatively newer developed product, as the Ultra Copper used to be their highest rated silicone. Thanks for posting. I think I'll switch to it.
Regarding the slate vs granite, I think you've made a wise choice given granites dislike for temperature, but coat the slate with a good quality sealer, to prevent fat and oil stains.

[nlinva]

Your granite front landing looks great! I have something similar planned for my oven, but in slate (and also with a simpler right angle joint -- I don't think I can do 45 degrees accurately enough :-)

As for the high temp silicon, Permatex's own website suggest that for even higher temperatures than the Permatex Ultra, you can use Permatex Optimum Red. Maybe worth a look.

For the rope, are you planning to put it right in the corner, or on the face of the arch, or on the side/top? I'm trying to think through what the pluses/minuses are of those options. On the face seems most straightforward, but on the side/top might make it less likely to get rope fraying accidentally enter the landing space, even if the silicon gasket fails. Not sure it would make a real difference, though.

[Toiletman]

Another tiny update: the first two rows of chimney are in, pointed and cleaned up to accept the BBQ griddle. Of course precision masonry remains an illusion. Even with a gap-tool I didn't manage to have the joints large enough to accept the aluminium 'rail' that I had planned on using to prevent wear by the griddle on the stones. Alas, the griddle itself fits and there's ample space for expension differences to be accommodated.

The search for a high temperature sealant posed quite a challenge. I found a black, fire proof elastic kit that I used to put in the granite slab. Turns out 'fireproof' was not actually fireproof, but a safety feature to delay fires... the kit starts swelling above 120C/250F . All the 'oven' kits that I do find say they're resistant up to 1200C/2200F, but non of them remains elastic. It seems this is the kind of product used to glue the 'fire rope' in place, with the rope offering the flexibility at high temperatures. So in the end I'll go with david s 's recommendation of Permatex Ultra for the high temperature flexible seal. Then I'll use the HT glue to glue in the fire rope around the back of the chimney. Similarly to mongota 's design, but with only one fire rope. See picture to clarify.

Cutting more bricks for the next rows will have to wait until the weekend, as it's hitting high temperatures around here again (30C/86F+).

[Toiletman]

Thanks for the tips david s, I'll have a look at the Permatex ultra. Not much progress on the pizza-oven here. Spend most free time last week on Ikea furniture for my daughter... but next to a new bedroom I did manage to almost finish the landing and cut the first stones for the chimney. Cutting the granite, and especially fitting it was quite challenging, but I'm pretty happy with how it came out. I decided to cut away the strange overlapping chimney stones and that looks much nicer. Loadbearing wise I don't think it's significant to loose a little footprint.
I'm still on the fence on the final design on top of the chimney arch: a brick chimney adds a lot of weight fast as well as producing the 'heat in your face' problem that I've been hearing about. I might end up going to make a cast, but let's first focus on getting the arch in. Looking forward to building up again

[david s]

On pressure on the arch remember that the thermal expansion and contraction cycling can compromise mortar joints so weight on top of the arch becomes more of an issue. This then requires either bracing or buttressing of the side walls that support the arch. The simpler solution most ovens employ is to reduce weight on the arch by using a thin lightweight stainless flue. Care should be taken and solutions found, to accomodate the expansion of the stainless that can stress the refractory or brick that surrounds it, as the conductive stainless expands before the brick or refractory.

On high temperature silicone the best I could find is Permatex Ulta Copper.

on brick sludge it could be used as an alternative for powdered clay because the saw creates such fine dust. However it contains some larger brick chips that would need to be removed as well as the sludge would need to be dried and sieved before ready for use, hardly worth the trouble.

[Toiletman]

Thanks Giovanni Rossi that will make it easier. Any answers to my other questions? david s you seem to be the chimney expert?

I decided to brave the heat and get a little bit more work in.... first to improvise an extension to the sawing table such that I could cut the granite windowsill... praying that I would't ruin it on the first cut I managed to get the cut in. Only to find out afterwards that the old 'measure twice, cut once' went up again... I didn't take into account that I should still slice 5cm/2" of width from the granite, so I cut the piece a little bit too large. Luckily it wasn't a problem as the standard window sill was half as cheap as getting the granite cut to size. The standard size leaves me with enough excess for this little mistake. Cutting the sides that will be covered in mortar to size was easily done.
To not risk chipping the front corner I have to flip the 'improvised support' to the other side and that didn't fit into the rest of the night anymore... so hopefully finish cutting the rest of the granite tomorrow evening and have it set in mortar before the weekend.

[Giovanni Rossi]

- What kind of mortar do you use for the granite landing? Just normal portland based mortar, or some type of tile glue?

My granite landing is 3 pieces. I used a bed of standard mortar mix on the brick base. It's held up just fine. Not much heat to worry about there.

[Toiletman]

With the last few holiday days I managed to put a little bit more work in. The design of my gallery is such that I first need to put the landing in, as it partially rests on it. I bought a black granite window sill that I should be able to cut to size, and have cut a lot of 'standard' bricks to lower height such that they will fit below the granite neatly. It was some puzzling to get neat joint spacing as well as and interlocking buttress and gallery wall.
With the current heat here I had to wait until evening to do the actual mortaring, but the bricks are now in. The mortar was past its 'best before date' so I was slightly worried it wouldn't set properly. Tonight I cleaned up the joints and they seemed to have hardened perfectly, so great result. I might do some actual pointing work before putting the granite in. Cutting it is also going to be quite exciting. Below some pictures, but first a bunch of questions:

- What kind of mortar do you use for the granite landing? Just normal portland based mortar, or some type of tile glue?

- Any recommendations on brands of high temperature silicone? I'm able to find several types, but am reading quite mixed reviews by people (ie. flushed out with the first rain, dries up hard, etc.). Especially some European brand recommendations would be very helpful.

- Still some time away, but for the Chimney I'll go for a double walled steel system. There's an anchor plate for sale for this as well, it contains a 'condensate' tap connection and is IMHO quite expensive. I'm wondering if such an anchor plate is needed, or if a homemade solution would be better. I do think the chimney to oven connection is quite a critical one for moisture ingress, like also demonstrated in several posts on the forum. Does anyone have recommendations/explanations of where exactly the condensation risk is, and how they have dealt with it?

[tmoskos]

To address your concerns, consider reinforcing the chimney arch with extra bricks or buttresses for added support. Your idea for a thermal break is solid.

[nlinva]

I think you're right that you'll probably need some buttressing. Your proposed set-up looks good to me. One possible alternative might be to make the side walls in the shape of an L, or a T on its side (when you're looking straight down at it from above). The part sticking out would add extra stability, which might be enough to counter the sideways pressure from the arched part of the opening.