2024 Neapolitan oven build

[Giovanni Rossi]

As others have stated, great masonry!

nlinva referenced my keystone is made of 2 standard firebrick. I just buttered them with a thin layer of mortar and clamped them overnight. A round keystone would have been fine, but I decided to try making a 12 sided one. I'm not sure which shape would have been easier because I had only an angle grinder to work with.

One point to share was that I trimmed and dry fitted the stone a number of times and settled on it resting about 1/4" below the last course. I could have trimmed it a bit more. I was surprised how much room the mortar took up and had to push it out and remove mortar 2 or 3 times. You can see that the joint it pretty tight. It took a bit more persuasion by my wife from above with a rubber mallet than I would have liked to get it in place. But, it sure "locked" everything together.

[daidensacha]

MarkJerling, UtahBeehiver

Thank you for your kind words, it means a lot given your status as experienced builders.

It’s been on my bucket list for 10 years now, since I first obtained the Forno Bravo plans those years ago. This last year I dove into Sketchup drawing and refining details, working out how I would do it. There is no experience like actually doing it though, and I gained a deep respect for all those who have done it. It’s hard work, working through problems and issues. I’m so glad I spent the last year working out details, and planning. Honestly, it would have been a disaster had I not. So far, it’s falling into place, and I’m trying to balance enjoying the process with the desire to finish it now. The two kind of work against each other, and I’m now leaning more to enjoying the process and it will be finished when its finished.

[daidensacha]

One more course leaves an awkward size hole for the keystone.

New batch of fire cement very different to the first lot I used.
I ordered a 25kg bag of fire cement as I ran out on Tuesday, and the supplier let me down. They didn‘t deliver so I ordered what looks like the same product from an alternative supplier and the bag was delivered yesterday. From the photos, and information provided I expected it to be identical, but it is very different to work with. Very easy and fluid, yet not runny, and grey instead of reddish black. The work time is much longer, and it reacts very differently when in contact with the Schamottsteine. It does not become instantly hard and unworkable when in contact with the Schamottstein like the precious bags. It is more like what I was expecting to start with.

That said, the weather this week has been overcast, cold and wet, with max temp today 13C, min 7C. I did the second last course yesterday, and cleaned it up this morning as the cement is still not set. As the horizontal gap was a bit bigger on this row I inserted slithers of Schamotte in the cement, and much easier with this batch of fire cement.

Anticipated size of Keystone hole to fill: ID 115mm, OD 145mm, is this to big?
As I come closer to the keystone, I‘m presented with an awkward size hole to fill. I have one more course which will leave me with an inner diameter hole of 115mm. On the outside this will be around 145mm diameter. I do have 2 extra 250x250mm floor Shamottestein, which I could use as I would be able to cut them big enough to fill the hole in one piece. I would need to cement one on top of the other as Giovanni Rossi did to make his keystone. I don’t see and alternative, other than to do one more course, which would require me to cut the width down from 64 to 40-50mm to allow a very small hole to insert a small keystone.

I‘m open to feedback, or suggestions if anyone has some experience with such an issue.

Adjusting width of IT brick holding plate as the bricks reduce in width.
One other small issue I didn‘t anticipate was the 50mm wide holding plate on my IT. It was too wide from this last couple or rows of bricks, so I was positioning my bricks to the side so it didn‘t impede the positioning of the brick, This messed with my angles though, and I only realised when finishing this last course that I need to cut the width down to 20mm so I can position the bricks on center, and this should do away with the problems I had these last courses of the angles. It’s ok, as I individually cut one side of each brick as I test fitted it to see what adjustment I needed to make. But I could have avoided this altogether had I realised earlier that I needed to reduce the width of the IT brick holding plate. Hopefully documenting this helps someone else if they encounter the same issue.

[UtahBeehiver]

Yes, I had to do something similar to the IT

[daidensacha]

Yes, I had to do something similar to the IT

That looks very much like mine now too. I hit it with the 125mm cutting blade to reduce it to 20mm wide today. It should do the trick for the last course.

[daidensacha]

Stainless steel reinforcement completed.

I’ve been going stir crazy waiting since 8th to get more fire cement. My supplier, “schamotte-shop.de“ is not being transparent at all, will not answer the phone, only reply slowly to emails and will not give any commitment to when I will receive it. They have been totally unhelpful. I ordered the same product from an alternative supplier who said they could deliver within 3 days. That supplier turned out to be also owned by them, and they sent me 25kg of the wrong product. I now ordered another bag from the second supplier who apologised for sending the wrong product. That should arrive today. I have my fingers crossed that it is correct this time. 2 weeks of good weather have flown by and I have not been able to finish the dome. Very frustrating not being able to work, watching the last good weather for the year disappear.

Here are a few little things I was able to do on the oven. I also finished the terrace paving, started on the terrace gutters, and put a soak well in the front garden to catch the rain water from the roof. Not the jobs I wanted to do, but good to have them done at least.

Stainless Steel Reinforcement
I got my galvanised reinforcing braces back from the engineering shop, so I got into that. The 45° angle on the braces was not perfect for securing my bolts. I bent the stainless threaded rod to fix this, and it works well. Two stainless anchor bolts secure it to the hearth slab, with stainless threaded rod securing each brace across the top of the arch.



Arch Vent Mount
One other little job I managed to get done was to cast a vent mount on top of the arch with a 50/50 mix of fire concrete and vermiculite. It’s strong, level, and my vent cast will fit perfectly on top.

[UtahBeehiver]

Looking good al all fronts

[daidensacha]

Keystone, or one more row of bricks.

I mentioned this previously because I foresaw this dilemma coming.

My fire cement finally arrived on Wednesday. I immediately did one more row of bricks, and I had to cut a lot individually as my calculation for the cuts with mr Chipsters jig were a little off, and I wanted the fitting to be as close to perfect as possible. Bear in mind, being a Neapolitan build, I adjust and reset the IT for each course to account for the changing height of the dome and angle of the bricks. It was very straight forward initially, but the last rows became more tricky to keep the small gaps I have been making.

Wednesday night at 2am, my mind was working on how to improve my setup for cutting more precisely. Yesterday in the morning, I took measurements of the hole diameter, and brick angle for the last row. Then I knocked up a 3D model in Sketchup to calculate how many bricks, with the size and angles required. It was much more precise, and of all 18 wedges, I needed to cut 3 individually to fit in the row.

The last 2 rows because so cramped for space to work, I removed the IT and put them in by hand, using props cut from a sheet of ply to hold the bricks in place until I got them all in.

Now I’m left with a hole 115mm on the inside of the dome, and 145mm on the outside of the dome.

Option 1. Cement 2 floor bricks together to make one thick enough to match the thickness of the dome, and cut one large keystone to fit the 115-145mm hole.
Option 2. Cut a few bricks to reduce the width from 64mm to 30 mm, and cut wedges for one more row which would leave a hole 50mm on the inside, and 64mm on the outside. It would be a much smaller keystone, but require a bit more work.

My last 2 rows added by hand without the IT as it became easier due to the lack of space to move the IT.



This was the 3D plan I knocked up for my last row of bricks, as seen above.



This would be my last row of cuts if I decide to add one more row. I would only need 2 bricks cut in half, and 5 wedges from each half. Might just cut them for the exercise. I had considered cementing them together, with the keystone in the center, before test fitting and adding to the dome.

[rsandler]

At least from the outside, that looks like very neat work on those last courses, especially with having to dispense with the IT. Nicely done!

I would just make a 2-brick keystone; on my first oven I actually made a 3-brick sandwich. Up to you of course, and if you enjoy the work enough to make half-height bricks to bevel, certainly go for it. Even you will rarely see, much less stare at, the top of the dome, and certainly no one else will. So, do whatever satisfies you at the moment.

[daidensacha]

At least from the outside, that looks like very neat work on those last courses, especially with having to dispense with the IT. Nicely done!

I would just make a 2-brick keystone; on my first oven I actually made a 3-brick sandwich. Up to you of course, and if you enjoy the work enough to make half-height bricks to bevel, certainly go for it. Even you will rarely see, much less stare at, the top of the dome, and certainly no one else will. So, do whatever satisfies you at the moment.

It’s a good point that no one will see it. It’s so true. I tried looking in from the front today, and short of crawling in, it’s really hard to see the top of the dome. Appreciate that feedback.

I hedged my bets and decided to do both, and see what works best.

Option 1. I cut the half height bricks, and then the wedges first up. It’s really hard to work in the small hole. I tried various ways to support the small wedges, but it became to finely so I removed them. I started cementing them together, and sixteen wedges are now 6 pieces drying. I tied strings around the wedges to see how how the come together, and it makes a slightly bigger piece than the hole in the top of the oven. That’s ok, because tomorrow I’ll put the six pieces together, then cut a keystone and fit it in the middle of the cemented wedges. I can then cut down the single piece to fit in the top of the oven, Maybe not the conventional way to go about it, but if it comes together it will look nice at least.

Option 2. I cemented 2 bricks together, and they are drying in the garage. I cut templates for the top and bottom of the hole, and will transfer those shapes to the top and bottom of the 2 bricks. Then I’ll cut it down to fit in the hole, and see how it looks. It’s a backup in case my wedges become to complicated, and may well become my first option if it looks ok.

I’m resisting the urge to rush, given the work its take to get to this point. I know in a few days I’ll be fitting the keystone, and will then be onto the vent and chimney.

[nlinva]

Your brickwork is amazing, and to a far greater precision than mine. For me, this meant that your option 1 was basically out of the question, so I went with your option 2, and it worked nicely for me.

I do have one caveat: in my case, the cemented-together keystone bricks did not hold together in the course of using the angle grinder to get the correct shape for the keystone. I had to do a fair bit of grinding, and when I was almost done, the two bricks came apart. This was not a big deal: I simply scraped away the mortar, cleaned the surfaces, and re-cemented them together, making sure to keep them oriented correctly relative to each other and to use the same thickness joint. But just something to be aware of that it might happen.

Also, while it is true that you'll never see the outside top again and rarely see the inside top (unless you make a real effort, you can of course take lots of pictures to remind yourself how good it looks underneath all the insulation that's going to come on top of it!

[david s]

Ben Guillford’s Melbourne Firebrick Company that sells a brick kit just replaces the last 3 or so rows with castable refractory and it is fired in place.

[daidensacha]

I have two separate options both in process and I’ll choose the one I prefer when it’s clear to me.

I managed to cement the wedges from option 1 above together and it’s drying inside overnight. I’ll cut down and cement a keystone in it. I figure in one piece it will be stronger. I’ll leave enough keystone sticking out the top to use as a handle so I can hold to drop it into the hole when fitting. Can cut that off after cementing it in. It’s very close to the hole size but will need some minor fitting adjustments.



I’ll also start cutting down my option two using the wet cutting saw to get my side cuts of the stone. Hopefully that will mean less grinding and the bricks will hold together.

[daidensacha]

Ben Guillford’s Melbourne Firebrick Company that sells a brick kit just replaces the last 3 or so rows with castable refractory and it is fired in place.

That’s interesting. I understand why, as it’s fiddly as when the hole gets smaller. I thought as I got to the last courses it would get easier, but it’s the opposite. Requires more care and attention to detail.

Does the castable refractory require firing to set?

It raises a question I have about two different types of fire cement/ mortar available here in Germany.

1. Hydraulic binding mortar. Binding/ setting process is chemically triggered with addition of water. Has 30% clay,
2. Ceramic binding mortar. Binding is made through firing at temperatures of around 800C.

I’ve used hydraulic binding cement, and gotten used to it. The bricks need to be wet, and once cement added I need to put it exactly in place within seconds of contact as the water is sucked out as soon as two bricks are in contact.

Ceramic binding mortar was sent by mistake in my last order and I laid a course using it. It was totally different in consistency, a dream to work with. Stays creamy even after bricks are together, and allows for easy adjustments once they are. Can add brick wedges in gaps very easily. I removed the course and mortar as I wanted to complete the oven using the hydraulic setting mortar. I was unsure how, and if the ceramic binding mortar would set with temperatures reached in the oven.

Do you know if it’s possible to use ceramic setting mortar on an oven dome? It would make life much easier fitting the bricks.

[david s]

Castable refractory uses calcium aluminate cement as the active cementious ingredien. Its fast setting and curing and refractory nature make it a suitable material. Using a conservative firing schedule up to service temperature, with the addition of burnout fibres, prevents steam spalling. The material only begin to vitrify above 600C, converting the chemical bond of the cementious proportion to a truly sintered body. This same material is used fore commercially cast ovens.

The other product you are referring to I think is a sodium silicate based one. Check the data sheet on the product for details.