2024 Neapolitan oven build

[daidensacha]

Keystone question

If my calculations are correct, I will have a hole with a diameter 120-140mm to fill with a keystone to finish my dome. I have my last three courses to do now before fitting the keystone.

I guess there would be many ways to do it, using multiple stones count to fit. It is feasible to cement two bricks together from which I can cut one piece to fill the hole?

[daidensacha]

Your anchors will be in a place that will be subjected to both heat and moisture, both of which accelerate rusting, be sure to use stainless anchors. Otherwise their failure in a position that’s not accessible easily, could negate the function of the stainless band.

Yes, I’m using all stainless steel, apart from the brackets which are steel, and will be galvanised. Brackets will be ready next week, hopefully I will have set the keystone in the dome by then and I’ll fix the brackets. Measure the required length for the stainless straps and have them welded to the tightening brackets which I’ll then be able to attach to the galvanised brackets.

[david s]

Your anchors will be in a place that will be subjected to both heat and moisture, both of which accelerate rusting, be sure to use stainless anchors. Otherwise their failure in a position that’s not accessible easily, could negate the function of the stainless band.

[daidensacha]

Reinforcing brackets being fabricated. Rainy weather slowing progress.

I thought it would get easier, but I kind of gave up on that notion, as with each obstacle sorted comes another. Now I’m just tackling each obstacle as they come and evolve. I did another course yesterday, the first that I couldn’t complete from inside the oven. That required developing a different skill set to lay standing on the outside of the dome. By the end of the course I got used to it.

I have 5 more courses to complete the dome now. The angles of the cuts are becoming a little more to think about. My next course is the first where I think I will reduce the size to 1/3 bricks to reduce the horizontal triable gap that is beginning to develop between the bricks.

I was at an Engineering factory of a friend yesterday, and he is welding up some brackets I designed to fix my stainless support straps around the oven. Should be ready in a week, galvanised to limit rust.

I made up a template out of wood just as an example, and I think it will work well. Each will fixed to the slab with two anchor bolts, and together with a threaded rod across the top of the arch. From this I made up my plans in sketchup. 50x50x5mm steel angle, galvanised.



The weather lotto here in Bavaria where I live isn’t good this week, cloudy with forecast rain. Yesterday I was lucky, today not. Ideally I would be happy if I have enough windows without rain this week to finish the dome so I can fix my stainless steel reinforcing straps around the oven, and get onto building up the vent. I need to complete this so I can start getting the insulation on the oven.

[Toiletman]

Inner dome brickwork.

Integrating the dome bricks with the arch was messy, and dusty. I cut the inside of the top of the arch to allow for easier nesting of the dome bricks.

I cleaned up the dregs today, set my IT for the new course, and took my measurements for the radius, and angle to make cuts tomorrow, weather permitting.

I also went around the inner joins of the bricks, repointing voids between where the bricks meet. It will not get easier as I progress up the dome, so want to keep it as good as possible while I have easy access.

As expected: impeccable masonry! It's looking really great and you're also making great progress. Like you I'm hoping the weather lotto will give us some more working days towards the wet and cold season....

[david s]

The second pic was after the final render coats. Your plan to do some small test batches is a good one. The grain sizes you posted for the vermiculite and the perlite are what I use.

[daidensacha]

david s Thanks David.

My designed base allowed for 100mm ceramic fibre blanket, covered by 150mm vermicrete. At the sides I will need to add that so the sides of the dome meet the sides of the base, but I can go thinner on top with the vermicrete. If I got you correctly, I’ll plan on adding 4 x 35mm layers of vermicrete at a time, a week apart to allow each layer to dry sufficiently before adding the next. Our fist frost is possible from mid October, but we can still have warm days. Weather lotto, will just have to be flexible.

I think I’ll knock up a small test batch of a few liters of homebrew to test it and get the hang of mixing it. The sizes of the vermiculite and perlite is hopefully going to work, as I mentioned some time ago, i had issues translating fine and medium into German measurement standards. Maybe I could break my vermiculite down a bit if its not fine enough.

1. 5 parts vermiculite (2-3mm)
2. 5 parts perlite (2-6mm)
3. 1 part portland cement powder
4. 4 parts water (added 1/3 at a time and hand mixed in bucket or barrow)
5. 1 handful of clay powder per litre of cement added

I figure I’ll test it to see how it sets up after a day. I’ll post my result, positive or negative and make any required adjustments from there if needed.

One question about the photos you posted showing the vermicrete being added directly over the blanket. The second shows a really smooth finish, is that only vermicrete, without render? If I can get something close to that finish I’ll be really happy.

[UtahBeehiver]

The P/vcrete layers are about 2-3" thick by 4-5" tall over 3" of ceramic blanket. I did not use any clay but I know David S advocated using some for work-ability.

[david s]

150mm thick vermicrete layer is very thick. I’ve found if you want a thick layer it is better not to go any thicker than around 35 mm. This takes around a week to dry in ideal conditions, any thicker and the moisture deeper in just doesn’t escape. If you want it thicker then do a second layer after the first one has dried. Excessive insulation is subject to the law of diminished returns. As well as insulating the v’crete evens out the lumps and bumps of the blanket as well as providing a firm substrate onto which you can apply the outer rendered layer, once it’s all dry and the drying fires have been completed.
This pic shows the vermicrete layer being applied over the blanket. Because it is a corner build (I hate corner builds) there was very little room at the sides. Two layers of blanket there but four on top. I also never bother with chicken wire over the blanket. I believe it's a waste of time, it compresses the blanket, reducing its insulation value. The vermicrete will restore the perfect shape you want.

[Frenchie]

What a beautiful build!

[daidensacha]

Inner dome brickwork.

Integrating the dome bricks with the arch was messy, and dusty. I cut the inside of the top of the arch to allow for easier nesting of the dome bricks.

I cleaned up the dregs today, set my IT for the new course, and took my measurements for the radius, and angle to make cuts tomorrow, weather permitting.

I also went around the inner joins of the bricks, repointing voids between where the bricks meet. It will not get easier as I progress up the dome, so want to keep it as good as possible while I have easy access.

[daidensacha]

UtahBeehiver Thank you. I hadn’t considered the issue of venting steam pressure to prevent issues with cracking render. Should be easy enough to add it on top of the dome when adding the v/p crete.

I like your hand made trowel device tip. Guessing your layers are about 6x6” with the trowel set to hold it until it sets hard enough to support itself? It’s very brown, did you also add powdered clay?

I have ceramic fibre blanket to go over the dome.



Enough to have 100mm over the dome, then 150mm of homebrew V/P crete over the ceramic fibre mat.

Dave did explain previously that it takes time to dry, so is wise to add it slowly enough to allow the layers to dry sufficiently before adding subsequent layers. Here in Bavaria, with the humidity, my season for adding it will end when the cold weather comes. Then it will freeze before drying. I’ll see how I go.

[UtahBeehiver]

David always gives great and detail instructions on v/pcrete. It is a weird stuff but it does hard up. I made a cheap curved trowel to hold the v/pcrete in place until it would stand on it's own. You cannot do too much at once or the material slumps. Each of my v\pcrete lifts were 3-4 inches high then I let it set up and added another layer the next day. You might want to consider placing a vent somewhere on the dome during this stage, I place mine near the apex of the dome, David places his in the chimney vent, others near the base. Either way, a vent allows water the gets into the dome to vent when the water sublimates from liquid to steam (volume increases by abt 1500 times) and has the potential to build up pressure under the finish dome surface and cracking it. PS we don't normally advocate a covered ceramic blanket (mylar foil/aluminum) any more but I punch a 1000 holes in the material so water vapor could move freely and out the vent.

[daidensacha]

david s As usual your tips and info is really helpful, thanks David.

I will try adding 1 part powdered clay to make it more sticky. I’ll also mix 50/50 Perlite with Vermiculite to make up the 10 parts per your homebrew recipe. I have about a week to finish the dome, then I’ll be building up the vent and then onto the insulation. It’s looking like it will be a wet week, which will slow down my progress, but expecting roof sheets mid Sept so then it will be under cover. Hoping to get as much Vermicrete insulation on the dome before winter sets in.

[david s]

Everyone has doubts about the mix the first time they make a batch, but it does set up hard after 24 hrs.High spots can be easily carved away and low spots filled with a second batch.
Your proportions sound about right but the water proportion does depend on the grain size. The finer the grade the more water is required. I find a mix of vermiculite and perlite works better than either of them alone. I use a 50/50 mix of medium grade perlite and fine grade vermiculite. I've mixed mountains of the stuff over many years and have found the best method is to combine the dry ingredients together then add the water slowly while mixing. This is best accomplished in a barrow so you can see what's going on as well as feeling the texture. Don't use a mixer as it sticks to the blades and mixer sides as well as abrading the grains.
If you have trouble with a 5:1 mix you'll find the 10:1 much harder. More cement to bind the grains just reduces insulation capacity. Also, because of a variation of moisture content from either manufacture, grain size or humidity, the water addition can vary. Too much water can wash the cement off the grains, too little leaves the mix somewhat dry. The correct amount is when the water just begins to pool in the bottom of the barrow when thorough mixing has been completed. To make the mix more sticky add a handful of powdered clay for every litre of cement added. For doing the over dome insulation create a wall about 6" high around the oven base, leave it for 24 hrs then proceed with more batches the following day. This technique avoids collapses when using a lean mix.

Mix the dry insulation mix in a bucket or wheelbarrow in the proportions by volume: 10 parts insulation mix: 1 part cement powder, 4 parts water.
(An empty ice cream container makes a handy measurer). Mix dry ingredients first then add 1/3 of the water and mix well, then the second 1/3,mix well and finally the last 1/3 of the water and mix well. Apply by hand but wear rubber gloves (or you’ll regret it) (Do not be tempted to add more cement to make the mixture more workable; more cement will reduce the insulation value)
.
Starting at the base of the oven, take a cricketball sized handful and press it against the blanket with one hand while making a flat top with the other. Hold the mixture in position for around 3 seconds. Aim for a thickness of around 35mm onto. (This will seem like a pretty weird mix and you’ll be thinking it won’t work, but it will set up hard enough.)

Proceed in this way all around the dome until you’ve finished the batch. (the mix will feel really unusual and you’ll have your doubts about it. You can leave it to set up for 24 hrs before building higher).

Continue making batches and applying it in the same fashion