2024 Neapolitan oven build

[daidensacha]

If your slab is level and CaSil board is true, unless your bricks aren't uniform, you should be fine. If needed, sort through the bricks to get the best match. You may just need to knock off any high points with a cup grinding wheel and an angle grinder...just use a low speed and go slow.

True, you'll not want to introduce moisture to your CaSil board. I know david s has green-lighted sand only before but cautions making sure the sand is very fine. I've had to sift sand at times for other projects. I just sneak the sieves out of the kitchen when no one is looking.

Thanks Giovanni, I laughed when I read you sneak the sieves out of the kitchen. Mums the word, I did the same yesterday with a bottle brush to clean out some drill holes in my concrete so I could fill them with epoxy.

I did play around with the bricks today when laying them out, and the surface is mostly very flat, luckily, apart from a few small areas that where it is like 1mm higher. I might use a little fine sand there when I lay them in place after cutting tomorrow. Alternatively I do have a concrete grinding cup for my 125mm grinder. I will be using it tomorrow to get the sides on the bricks rounded to shape once cut, so I can get a feel how it works on the refractory bricks. It will only need minimal taken of the joins in a few places.

I still need to make up a wooden block to fit in place of the center brick where I will mount the indispensable tool. Will do that tomorrow as well, once I have the side cuts done.

[Toiletman]

You were going to build your dome directly onto the floor bricks right?

After finishing the dome, I replaced some ugly cut bricks in my gallery floor. To do that I had to take em all out, so I also re-leveled them (all my floor tiles have a (dry) clay/sand mix underneath them). In doing that I noticed that there's quite a jump from the stainless steel heat break to the floor tiles. This seemed to be significantly higher in the middle (1mm) as to closer to the dome walls (~0mm).
So it seems that my floor tiles were seriously pushed down by the weight of the dome. So if you put sand underneath: ensure you put some heavy load on all of them (ie. your jumping? ) and/or hammer all of them in place. I did this, but apparently not hard enough. In the end however, all of this is fixable with the grinder .

[daidensacha]

You were going to build your dome directly onto the floor bricks right?

I made the template for marking the flooor brick cuts so they lay within the oven dome and arch. The dome and arch will sit directly on the calcium silicate sheets.

I allowed for 3mm gap between oven floor and dome wall. A 2mm gap between gallery floor and arch wall. I’m still undecided if I will include my heat break in the gallery floor.

Once my floor is cut to shape, I’ll repurpose my ply floor template by cutting it in half, and lay it over my floor during the dome build for protection. It should also allow for more even weight distribution should I need to stand of the floor. It will also catch any mortar spill, keeping the floor nice and clean. Just need to cut it so I can get the pieces out through the arch when the dome is up.

[daidensacha]

Heat break filling

Toiletman last post made me aware I need to work out some issues around my heat break. I need to consider and plan now to save limiting my options when I come to integrating it.

I planned for a 12mm/ 1/2“ heat break directly after the inner arch. Illustrated in the image with blue.



What I didn‘t fully nail down yet was if I also include it in the floor, what to use to fill the gap, and how to seal it at the floor level.

I‘m curious what other have used, and recommend.

I have ample vermiculite and perlite for over the oven, so I could make up a brew to fill the space.
I could also get some 13mm ceramic fibre blanket to insert in the space when building the outer arch.
I saw mention of using stainless steel, but i‘m not sure how that is used, and implemented. Is it worth considering?

With regard to sealing the gap, I was thinking that using fireclay mortar to cover the inserted insulation, maybe the last 10mm of the gap.

I would definitely be simpler and save me extra work to cut the break in the floor bricks now while laying the floor.

[rsandler]

You should have a gap at the floor (your floor bricks will conduct heat too). 1/2" is pretty wide, but you can just fill with cardboard or something similarly flammable to keep the space, which will in due course be replaced by ash, which is a reasonable insulator. Or you can leave an air gap, which will again end up filled with ash in due course. I think on my first oven I did cardboard, and on the second did 3-6mm of Nomex felt, which didn't come all the way up to the floor level, so the rest filled with ash.

[Giovanni Rossi]

daidensacha I seem to recall someone wanting to us a lean vermiculite or perlite mix to fill the gap and there was a recommendation to use a refractory concrete mix (heatstop?) instead of portland cement.

Obviously you'll want to isolate from your cooking space any kind of ceramic fiber product if you use one.

I know you're asking about a floor gap, but I assume you'll also be using a heat break at your arch. Take a look at Mongo's build. His break is my favorite. Had I decided to build my oven from scratch, I was going to emulate his technique.

Back to the floor. I'm not sure I've seen it, but Mongo's arch concept could be applied there using a gapped half lap joint with an insulator or just leaving an air space.

[daidensacha]

You should have a gap at the floor (your floor bricks will conduct heat too). 1/2" is pretty wide, but you can just fill with cardboard or something similarly flammable to keep the space, which will in due course be replaced by ash, which is a reasonable insulator. Or you can leave an air gap, which will again end up filled with ash in due course. I think on my first oven I did cardboard, and on the second did 3-6mm of Nomex felt, which didn't come all the way up to the floor level, so the rest filled with ash.

Thanks, yes I decided on adding the heat break in the floor. 12mm is a lot if I was to leave it to fill with ash, but I wanted to add insulation. My first thought was rope insulation, and I was considering vermiculite/ perlite homebrew, but I bought some ceramic fiber mat today. I was relatively cheap for a 2000 x 600 x 13mm sheet. I can cut it down to leave space inside the arch to fill with firebrick mortar.

I will go with my 12mm gap between the inner and outer arch, filled with ceramic fibre blanket, covered over with firebrick mortar. I will reduce heat conduction between the inner arch and the gallery outer arch. I can use the excess blanket around my flue above the vent.

[daidensacha]

Giovanni Rossi

Thanks Giovanni. My first idea was to just fill the gap with rope. I checked out Mongo‘s solution, and it looks interesting. Today I bought some ceramic fibre blanket, 13mm thick which I will cut to fill the gap. I can add rope along the inside of the arch, with firebrick mortar over it, or same without the rope. I will put the 12mm gap in the floor as well.

This was the ceramic fibre blanket. Left over will be used and not wasted.

[Toiletman]

Giovanni Rossi

Thanks Giovanni. My first idea was to just fill the gap with rope. I checked out Mongo‘s solution, and it looks interesting. Today I bought some ceramic fibre blanket, 13mm thick which I will cut to fill the gap. I can add rope along the inside of the arch, with firebrick mortar over it, or same without the rope. I will put the 12mm gap in the floor as well.

This was the ceramic fibre blanket. Left over will be used and not wasted.

Instead of using mortar you can consider putting high temperature silicone: it will flex with the expansion differential between chimney and dome, instead of the mortar which will probably crack. I've been trying to find a recommendation for a European brand, but haven't found one yet. You do want to make sure to have sth in between ceramic fires and your food area.

PS: my gap is 1", fitted with a 1" stainless steel square tube. Stainless steel: low thermal conductivity, doesn't rust in the rain/moisture that it will inevitably see. Aluminium conducts heat very well, so I didn't consider it for a heat break material. As my bricks are around 2", the other 1" was nicely fit with a piece of calcium silicate (1" thick). Thinking about it now I should've filled the tube with vermiculite, as it's large enough to allow circulation to exist inside... but alas...I'm not going to drill a hole in it now to try to get it to flow in.

PS: it would have probably been just fine to put loose vermiculite under your heat break tube, if you close it in from the sides with some tape or cardboard until your bricks are in.

[daidensacha]

Marking the floor bricks the right way.

Yesterday I used a ply template I made to mark the cuts for the floor bricks. Then this morning I removed the center floor brick, did some calculations to work out the height I wanted the indispensable tool to be mounted. I cut a 20mm piece of water resistent ply to replace the center fire brick and mounted the indispensable tool. After I place it in the middle of the oven floor, I checked the cut lines with the IT, and discovered they didn‘t line up exactly. Oops.

I erased the incorrect lines, and remarked the correct floor diameter with the IT. Then I cut the bricks using the wet cutting saw. At the end of the day I cleaned the saw, and I was surprised at the firebrick sludge that had settled in the bottom of the saw water reserve. Can I use this sludge perhaps under the floor bricks to level them? I would just need to sieve out the pieces of firebrick so I can have the fine sludge, but it seems to settle and takes work to break it up.

h

[daidensacha]

Instead of using mortar you can consider putting high temperature silicone: it will flex with the expansion differential between chimney and dome, instead of the mortar which will probably crack. I've been trying to find a recommendation for a European brand, but haven't found one yet. You do want to make sure to have sth in between ceramic fires and your food area.

PS: my gap is 1", fitted with a 1" stainless steel square tube. Stainless steel: low thermal conductivity, doesn't rust in the rain/moisture that it will inevitably see. Aluminium conducts heat very well, so I didn't consider it for a heat break material. As my bricks are around 2", the other 1" was nicely fit with a piece of calcium silicate (1" thick). Thinking about it now I should've filled the tube with vermiculite, as it's large enough to allow circulation to exist inside... but alas...I'm not going to drill a hole in it now to try to get it to flow in.

PS: it would have probably been just fine to put loose vermiculite under your heat break tube, if you close it in from the sides with some tape or cardboard until your bricks are in.

Thank you, that’s really helpful info for my application. I was curious how you used stainless steel. Could also use stainless U-profile with ceramic fibre board under it. Then the ceramic fibre board could also fit inside the U-profile. That sounds like a good solution to me.

[Toiletman]

Marking the floor bricks the right way.

Yesterday I used a ply template I made to mark the cuts for the floor bricks. Then this morning I removed the center floor brick, did some calculations to work out the height I wanted the indispensable tool to be mounted. I cut a 20mm piece of water resistent ply to replace the center fire brick and mounted the indispensable tool. After I place it in the middle of the oven floor, I checked the cut lines with the IT, and discovered they didn‘t line up exactly. Oops.

I erased the incorrect lines, and remarked the correct floor diameter with the IT. Then I cut the bricks using the wet cutting saw. At the end of the day I cleaned the saw, and I was surprised at the firebrick sludge that had settled in the bottom of the saw water reserve. Can I use this sludge perhaps under the floor bricks to level them?

On the marking: good job on the check twice before cutting... I also made a measuring oops today and also cut it... luckily I made the cut too large, instead of too small

For the sludge: I think this is what could then be sold/used as fireclay if I understand the comments here correctly (after sieving very finely, and drying). I wouldn't use it wet on calciumsilicate due to its dislike for water (the calciumsilicate becomes 'pulpy'). If you have some kind of waterproof layer or the waterproof insulation material you might consider using it wet.
After the layer became too large I took it out with a bucket, I'm up to two buckets by now, but they take ages to dry... not sure if I'll do anything with it or in the end it will just go to the construction trash section of the recycling center.

[david s]

Thank you, that’s really helpful info for my application. I was curious how you used stainless steel. Could also use stainless U-profile with ceramic fibre board under it. Then the ceramic fibre board could also fit inside the U-profile. That sounds like a good solution to me.

The stainless might look pretty, but it is a poor solution as an insulator. The thicker the wall thickness of the tube, the more heat it will conduct and transfer across the gap. While stainless is less conductive than mild steel, it is still many times more conductive than firebrick. So if you want to replace firebrick with a material that insulates then a highly conductive material is not particularly effective. As the gap’s primary function is to act as an expansion joint. Filling it with a square tube will not provide any flexibility. Perhaps a thin (0.5mm) u shaped tube might have sufficient flex to accomodate the expansion. Filling it with blanket would be better than just air.

My solution is to fill the gap with blanket to within 5mm from the top and fill that last bit with 5:1 vermicrete which is somewhat flexible and seals away any ceramic fibres. In my design it’s too hot for high temperature silicone to work there. Other fireproof caulks I’ve tried just go hard and fall out.

[daidensacha]

Soldier course and inner arch

I laid out the soldier course full bricks to see how they fit, and how many were needed. 40 bricks in total. I was actually surprised how they sit on the insulation layer, very sturdy and not as slippery as I had feared. It was my major concern with the weight of the dome sitting on top that they would slip and blow out.

I decided on using the full bricks for the soldier course, confident that with the bond of the cement joining them, and the stainless steel strap that will go around them to reinforce the lower course will be sufficient. Additionally, with layers of insulation outside the dome (ceramic fiber blanket, and 20cm of vermiculite/perlite homebrew) I‘m pretty confident it will hold.

I cut a 12mm heat break in the floor between the outside of the inner arch and the vent gallery. I cut a 12 mm ply profile to keep the gap correct until I fill it with 13mm ceramic fibre blanket topped off with 5/1 vermicrete.

To the brick laying. It was 30 degrees, and I soaked the bricks for a good 40 minutes until they stopped bubbling before taking them out of the water for the surface to dry off a bit before laying. Man, it was not easy, and definitely have a new found respect for those who build their own oven. It took me a good 5 hours, laying, relaying, relaying, relaying until I was happy with the positioning of the bricks, and that the mortar bond was good with the bricks.

I read a lot about how the bricks suck the water out of the mortar, as at 30 degrees it was instant when I put the bricks together. Even with wet bricks. I suspect my buttering was not perfect, and I just kept repeating until I got it done.

Saturday I cut the inner arch bricks with the wet cutting saw, to my specs from my design in sketchup. Fitting them then on my template to make sure they fit with sufficient gap for mortar.

We had 2 days of non stop rain, and my bricks sat out in it. I figured it wouldn‘t hurt, and might in fact help when I come to lay them. This morning, overcast with no rain, cooler weather, so got out early to do the arch. Making use of cooler weather and no rain. I made small batches of mortar, and my buttering was much better. Positioning the bricks precisely and moving them into place within seconds before the water disappeared worked much better than when I laid the soldiers. It was very quick, done in a few hours.

I know some might ask or suggest that I use full bricks for the sides of the arch. Actually the inner bricks directly under the arch are 114mm wide, but also 140mm long so I could cut the inside face to the shape of the inner dome. Had I used a brick width wise, I would have needed to cut a small piece to fit inside, and I didn‘t want to do it that way.

[daidensacha]

Inner arch

I removed the form from the inner arch this morning between showers. Amazing how the mortar drying process differs in cooler weather. 20C yesterday when I did the arch in the morning, and in mortar was still wet at night time. This morning set like rock.

I watched to remove the form to clean up the inner face of the arch, and point up any voids in between the bricks. Glad I didn‘t leave it as it was a bugger to chip away off the bricks. It cleaned up well. Quite happy with the result.