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]

weeks in perfect drying conditions

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