2024 Neapolitan oven 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

[daidensacha]

Vermicrete Questions

I have a question about mixing the vermicrete.

I understand different mixes are used depending on the application. i.e. 5/1 vermiculite/ portland cement for insulation under the oven, or where stronger is better, and 10/1 for insulating above the dome.

I’m using 1-2mm vermiculite which is very dry. I’ve now made a few batches. When I made the mould for casting my fire concrete vent, and now also for the heat break.

The batch for the heart break was 5/1/2, 5 part vermiculite, 1 portland part cement, 2 part water by volume. What I don’t get is a mix that then holds together in a ball. I mean, it does form a ball but that ball then falls apart pretty easily. I imagined it should form a ball that holds together. Is this right?

I’m asking because I can’t imagine when it comes soon to adding layers of 10/1 vermicrete over the dome, it will have half the cement volume to bind the vermiculite.

I’m wondering if the vermiculite being so dry just absorbs the water, not leaving sufficient for the cement to create a sufficient binding agent? Is it worth a) pre wetting the vermiculite, and b) premixing the cement and water into a slurry before adding it to the pre wetted vermiculite?

All that said, for my homebrew above the oven, I bought vermulite and perlite, so I was planning on making a homebrew mix using both with cement and water.

I could use some feedback on the issues I noted in this past though. Much appreciated in advance.

[daidensacha]

Heat Break completed and Dome started.

After a week laid up crook with COVID, I jumped back in work on the oven.

I filled the heat break with ceramic fibre insulation, leaving about 2cm around the sides which I then filled with 5/1 vermicrete. That’s inside and outside the arch to seal the ceramic fibre inside the arch heat break.

Tuesday I started the dome courses above the soldier course. Yesterday I completed the fifth course, which takes me above the arch. I’m relieved to have completed the integration of the dome bricks with the dome. It’s not perfect, but overall I’m happy with the result. I still have a few pieces to add in where the 4th course meets the arch under the fifth course.

The IT has been a godsend, making it much easier to position and set the bricks in place. Given mine is a Neapolitan dome, I need to adjust the IT for each individual course. I’m working from a template of the dome shape cut out of ply, so I can keep to the line of my designed curve.

Courses 1-4 above the dome required cutting side mitre and bevels, and tops and bottoms of the bricks so they transition from 64mm outside, to 40mm inside. Subsequent courses don’t require cutting tops and bottoms, only the mitre and bevel side cuts.

I knocked up a simple jig based on Mr Chipsters brick cutting jig. It’s worked beautifully, mostly. I haven’t quite figured out how to adjust it precisely when cutting smaller wedges, as it changes the mitre and bevel angles it seems. I have been adjusting it on the go making small cuts and checking, not wanting to waste bricks. By my calculations, I have about 20 bricks spare, which I would like to use on building up the sides of the arch to create a flat surface to mount my vent over the arch.

[daidensacha]

What mortar to build up bricks around outer arch vent and chimney?

I have a question about the construction of my chimney, mainly what type of mortar to use for the bricks surrounding the insulated vent and flue.

I have a pallet of historical hand made clay bricks that I am planning to use to build up the form around the chimney. I cast my own vent out of fire resistant concrete, which will sit on top of the arch vent. Schamott adaptor plate with 2 x 300mm long flue sections will sit on that.

I plant to wrap the cast vent, with schamotte flue with fire blanket, then to brick up around it leaving space between the fire blanket and bricks. I could either leave that space, or fill it with loose vermiculite. I explain this because I don’t see the surrounding bricks being exposed to high temperatures, and think I can use normal cement mortar to build up the bricks.

I do need to build up a flat section on the arch for the cast to sit on. I had planned on using firebricks, but am now wondering if it could be worth considering homebrew vermicrete (5/1 mix)? Vermicrete would reduce heat conduction up into the brickwork above the vent area.

Image of my planned chimney, along with the cast vent with schamott adaptor and 1 x flue that will sit above the oven arch vent.

[UtahBeehiver]

Not disappointed, very impressive timber works.

[daidensacha]

The big C variant seems to making the rounds, several friend and family have gotten it. Glad you are on the mend. Your brick work is really nice quality and top notch, expecting to see something similar with you timber works.

Thank you for your kind words.

I cut all the timber at the workshop of a family connection, as it was all so big. Longest lengths were 9.8 meters, with main front beam 200x100mm around 100kg. The rafters @ 200x80x5400mm were much lighter, but still a two man lift on the ground. It was much easier to cut all the joints and pre drill holes, fit locking plates prior to moving here and building it up. 2 days cutting and fitting, 1 day painting with transparent white oil, and half a day to put it up with help from family. 5 of us to lift and move it all into place. Brother in law brought his tractor with the forks on the back to lift the main beam up so we could settle it on the posts. That was the hardest part, but it went well.

Some pictures of the cutting and fitting.



The timber in place above the oven ready now for the sheeting.

The paving is 9 x 5 meters, with the roof 9.8 x 5.4 meters having 400mm overhang. It’s 3.5 meters high where it attaches to the wall, and 3.1 meters high at the front of the terrace. I did the plans myself in sketchup, using nice solid laminated pine timbers. Posts are 160x160x3000mm. Am using insulated sandwich sheets for the roof.



The balconies on the side of the house will be extended 2 meters, with a staircase allowing us easily to walk down to the rear terrace, pizza oven and garden. I’m running out of time to do that now this summer, so it will happen in the beginning of next spring. Now focussing on finishing the oven and rear terrace.

[UtahBeehiver]

The big C variant seems to making the rounds, several friend and family have gotten it. Glad you are on the mend. Your brick work is really nice quality and top notch, expecting to see something similar with you timber works.

[daidensacha]

Outer Arch progress

Timber was delivered on the 14th, so that week became prioritised for building and putting up the timber framework for the terrace that will be over the oven. Roof sheets will be delivered mid Sept, so wanted to finish that and get back to the oven to do as much as possible before the roof sheets come. Ideally would like the chimney done so I am ready to cut the hole in the roof to install the double walled flue. That took me from 14-17 August.

Then back to the oven, and I decided to complete the front arch before starting on the dome bricks above the soldiers. Like the inner arch, I found the inner arch pretty straight forward and surprisingly easy to lay the bricks. I can only hope I find the dome bricks are as easy to lay.

I put a piece of 10mm ply in-between the rear and front arch to maintain a consistent gap in which I can insert the ceramic fibre covered with homebrew 5/1 vermicrete. It worked perfectly. I’m also happy the vent is exactly the size I planned on in sketchup, so my homemade vent cast will fit perfectly on top.

I knocked up an adjustable jig for the wet cutting saw so I can cut the top and bottom angles on the dome bricks. My first four courses above the soldiers are crucial to setting the curve of the Neapolitan dome. I tested my homemade jig for cutting the left and right sides of the dome course bricks, and it works perfectly. Photos to come.

I am planning on fitting the steel angle braces that will secure the stainless steel straps around the soldier course. I will update more info on this soon.

I tested positive for COVID this week, and it knocked me for six. Been layed up since Wednesday unable to do anything on the oven, but back on the computer today planning. Hope to be back on the dome tomorrow, will see how my energy levels go.

[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.

[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.

[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.