70cm Homebrew Pizza oven build, Manchester, UK

[loumw]

Me and my mate Oscar have taken on the fun (but challenging) task of building a pizza oven. Found this forum not so long ago and it’s been great reading through other people’s builds, so we thought we’d start putting ours up too! We’ve already been introduced to david s and UtahBeehiver from a previous post who’ve been really helpful, and they also pointed us towards Nick J C build which has become a bit of a bible for us recently.


So, where we’re at:

We built the structure out of reclaimed bricks — 11 courses high and 2 bricks wide. Apologies for the bricklaying, repointing is to come! On the top layer we only laid the outer bricks so the concrete slab could sit on a ledge for support. We also added a shelf underneath for wood and pan storage.

Once the concrete had set we poured a perlite/cement mix at a 5:1 ratio to a depth of around 50mm (some areas were a touch deeper). This came approximately 10mm short of the top layer of bricks which gives a nice enclosed effect for the oven.


Planning the dome:

Moving on to what has been the trickiest part. Figuring out the dimensions for the dome, layers, flue gallery and how it all connects. To be honest the depth of layers and dome dimensions were straightforward enough, it was more understanding the flue gallery sizing and how that integrates with the oven correctly.

We’ve settled on a 700mm internal diameter with a 350mm internal height.

For the arch opening we’re going with 390mm width, 220mm height (62% of internal dome height), 170mm height for the edges, and 250mm depth (the length of our firebricks). At the end of the firebrick length we’re adding a 20mm internal lip all the way around the top and sides to act as a door stop, giving us the option of regulating temperature. We’ll have a 150mm flue set 50mm back from the front of the arch. When creating the framework we’ll add an extra 5mm diameter for the flue to allow for expansion, filling in the gaps afterwards.


The mix:

We’ve decided to go with a homebrew refractory mix, which David S recommended at a 3:1:1:0.5 ratio — sharp sand, cement, hydrated lime and fireclay. And Polypropylene fibres too. The fireclay was reduced to 0.5 parts to allow for shrinkage and reduce the chances of shrinking cracking. This will be applied at 50mm depth over a sand mould, shaped to the internal dome dimensions. Once the dome has set enough, (around 24-48 hours), we’ll remove the sand mould and fill any gaps or cracks with the same homebrew mix.


Outer layers:

From the homebrew dome outward our layering will be:

• 50mm Homebrew

• 50mm ceramic blanket

• 50mm vermicrete (vermiculite/cement mix)

• 25mm render

Total depth from inner dome wall to outer render: 175mm


Firebricks:

Yesterday we laid the firebricks which ended up being fairly stressful as our blade blunted mid-cut and being 4:30pm on a Sunday made finding a replacement interesting, but we got there. Really happy with how they’ve come out. We added 100mm onto the internal diameter (50mm all the way around) to give the homebrew mix a ledge to sit on and hold the firebricks in place.


Next up, building the sand mould and getting the dome started. Will keep posting as we go!


Any feedback or opinions would be very much appreciated!

Cheers, Louis and Oscar

[david s]

Wow, you guys are proceeding quickly. Your 50 mm of 5:1 underfloor insulation is certainly on the thin side and you probably should have given it way more time to dry before building over it. Not a huge problem, but it will take you way longer (probably months) for it to dry properly. You have planned well, so please continue the great documentation for the benefit of others.you’re on a fun journey.

[loumw]

Wow, you guys are proceeding quickly. Your 50 mm of 5:1 underfloor insulation is certainly on the thin side and you probably should have given it way more time to dry before building over it. Not a huge problem, but it will take you way longer (probably months) for it to dry properly. You have planned well, so please continue the great documentation for the benefit of others.you’re on a fun journey.

Thanks for the reply and interest David. Ahh right, that’s interesting to know. We haven’t started the build over of it yet, just placed the bricks on to visualise how they’d look, they aren’t set yet if we need more drying time! How would we know when it’s properly dry? It’s felt very dry and hard for over a week now which is why I’m wondering.

[david s]

Thanks for the reply and interest David. Ahh right, that’s interesting to know. We haven’t started the build over of it yet, just placed the bricks on to visualise how they’d look, they aren’t set yet if we need more drying time! How would we know when it’s properly dry? It’s felt very dry and hard for over a week now which is why I’m wondering.

Try buying a cheap garden moisture meter and pushing it to the bottom of the vermicrete slab. You may need to drill a pilot hole for it as the 5:1 will be pretty firm. It will take a minimum of a couple of weeks in perfect drying conditions. Read my experiment on drying a vermicrete slab (attached) which shows it takes longer than it looks. You may also want to consider drilling some weep holes through the supporting slab fro underneath which will assist the exit of moisture. This is good insurance for when you get water intrusion into the oven at a later date, which will accumulate into the underfloor insulation. Search "weep holes"

Vermicrete insulating slab PDF.pdf

[loumw]

Try buying a cheap garden moisture meter and pushing it to the bottom of the vermicrete slab. You may need to drill a pilot hole for it as the 5:1 will be pretty firm. It will take a minimum of a couple of weeks in perfect drying conditions. Read my experiment on drying a vermicrete slab (attached) which shows it takes longer than it looks. You may also want to consider drilling some weep holes through the supporting slab fro underneath which will assist the exit of moisture. This is good insurance for when you get water intrusion into the oven at a later date, which will accumulate into the underfloor insulation. Search "weep holes"

Vermicrete insulating slab PDF.pdf

Thanks David. Totally get it from your pdf attached now, going to order one of those moisture meters to test that. We did put on the perlite layer on the 5th of June so hoping it’s fine! Been building the arch framework over past couple of days. Posting about that below.

[loumw]

Been building the gallery cast framework over the past couple days. It’s all taped up and ready to go for the sand mould which hopefully doing Monday. Smaller structure on the back is for the internal 2cm lip to act as the door stopper. The front arch that sticks out is so we know when our homebrew mix is at 5cm of depth around the structure, and so it’s also held in place at the front!

[david s]

I hope you made your plywood mould easy to dismantle and remove because it will probably require pulling apart piece by piece and being sacrificial.

[UtahBeehiver]

What is your planned usage of the oven? As mentioned by David S earlier, 50mm if 5:1 pcrete is on the light side of insulation (equal to about 1" CaSi) normally we recommend at least 2" of CaSi or about 4" 5:1 pecrete. This level of floor insulation allows the oven to be used for multiday cooking. You could add and additional 2" of pcrete right under the floor bricks. Worth considering if you plan on fully utilizing what these ovens are good for.

[WaterDog]

Jumping in to reiterate what DavidS said. With everything screwed together, how do you expect to remove the mold once the cement has cured? The tape will help it release but it’s encapsulated in cement. Unless you’re planning on building the dome separately and upside down, I don’t see how you will be able to remove this.

Edit: Perhaps you’re planning on placing this to create the opening/rebate for the dome cast only and will cast the gallery as a separate piece? That could work. My initial thought was you were going to place this, build the sand mold and cast the dome/gallery as one piece which would be problematic. If you are planning on the separate dome casting, shim the wooden mold 1/8” or so before you start. When the dome dries, remove the shims, tap the mold to release and slide out.

One other comment. You may want to consider creating a higher/wider funnel shape to help draw smoke up the chimney. Can’t hurt.

[loumw]

What is your planned usage of the oven? As mentioned by David S earlier, 50mm if 5:1 pcrete is on the light side of insulation (equal to about 1" CaSi) normally we recommend at least 2" of CaSi or about 4" 5:1 pecrete. This level of floor insulation allows the oven to be used for multiday cooking. You could add and additional 2" of pcrete right under the floor bricks. Worth considering if you plan on fully utilizing what these ovens are good for.

Thanks for the reply UtahBeehiver. Yeah we’re now questioning where we originally got the number 50mm from as hearing from you guys and doing more research into it we’ve realised it’s probably not enough for what we want! We’ve decided to buy a ceramic fibre board and add that underneath our bricks to add as another layer for our insulation stack. We’ve found 25mm ones so the plan is to go with that. Been a busy week so unfortunately both not found the time to crack on with as much as we would’ve liked!

[loumw]

Jumping in to reiterate what DavidS said. With everything screwed together, how do you expect to remove the mold once the cement has cured? The tape will help it release but it’s encapsulated in cement. Unless you’re planning on building the dome separately and upside down, I don’t see how you will be able to remove this.

Edit: Perhaps you’re planning on placing this to create the opening/rebate for the dome cast only and will cast the gallery as a separate piece? That could work. My initial thought was you were going to place this, build the sand mold and cast the dome/gallery as one piece which would be problematic. If you are planning on the separate dome casting, shim the wooden mold 1/8” or so before you start. When the dome dries, remove the shims, tap the mold to release and slide out.

One other comment. You may want to consider creating a higher/wider funnel shape to help draw smoke up the chimney. Can’t hurt.

Thanks for the reply as well WaterDog. We’ve made the framework with the dismantle in mind so we think it should come off fairly easy, (fingers crossed). We have planned on doing the dome cast and arch cast at the same time as to be honest, Nick J C’s build is one we were told about and very much admired and are somewhat using as a base to go off. The way he did it is very similar to what we’re trying and he seemed to do it all in one go with a wooden built galley like ours and his seemed to come out great so just hoping ours would work the same.

[UtahBeehiver]

Good call on the additional CaSi. You are spending all this time and energy on the oven you might as well do it right and enjoy the full capability of a WFO oven.

[WaterDog]

Looking forward to the rest of your build.