Finally decided on 32in castable dome

[Mullster]

Sourcing materials in the UK (mid-lockdown)

So it’s been a bit challenging at times getting materials and I’ve struggled with the decisions around firebricks for the floor and the clay for the home brew mix.

In the end it was relatively easy to get sand, cement and hydrated lime from a builders merchant (and cheap too) and I had already sourced a large bag of vermiculite off Amazon a couple of months back when I was going to do a gym ball dome like I’d seen on YouTube (before I learnt so much on this forum!)

Clay
The clay is still not sourced - found several sites with links people on here have sharedaaronpizza andPoochdog12 thank you. But I still haven’t figured exactly which clay to buy so any experience would be welcome there especially from the UK contingent.

Firebrick
So I done so much looking for the bricks. Vitcas website has them at what appears a good price (less than £2 a brick) however by the time you get to shipping costs it’s up beyond £3 a brick.
Also they are 3” depth and I’m getting concerned about the overall height of the Oven floor relative to where I will be stood.
Instead with some advice from DavidS I looked into storage heater bricks as a resource that several UK oven builders have used. There’s a fair old trade of them second hand (and new if you prefer) and the price is good. The bricks are slightly larger and squarer so I need fewer, they are 2” thick instead of 3 and I have a seller at £1.50 a brick so I think I’m going to plump for those. For whatever reason haven’t committed to it yet. (This project is ridiculous - I make far bigger decisions at work much more easily!)

So that’s up to date - today I’m hoping to create the vermicrete insulation layer for underneath the floor. I’ll share some details of that later.

[Mullster]

Having the hearth poured

So again went for a company that brings the concrete from the roadside truck to your project. This time they were an hour late which clashed with a work meeting I had so I even had to let them do the leveling. This felt weird like I was cheating but I had no choice and the guys were really interested in the project and asking me loads about it. They did a fine job and I trowel smoothed it as soon as I could.

My mistake

The day of the pour it was windy and sunny and I didn’t cover the fresh concrete. I believe it started to dry too quickly which is why I’ve ended up with a hairline crack on the surface of it. I covered it later that night and left it covered and watered for several days after. The crack hasn’t developed or widened and I’m confident that structurally it’s all ok. Also the oven floor will completely cover the crack so no cosmetic problem either.

A few pics below

[Mullster]

Right guys - due to the site hack many of the recent posts on this thread have been lost so I’m going to post a bit of info bringing you back up to speed with my build. I’m conscious that this site provides a great amount of value for me with a community who have experienced it all before and those who are going through it at a similar time and I love the fact we can ask questions of each other as we go along. If I miss detail out in this catch up please just ask.

[Mullster]

Progress pics from yesterday

[UtahBeehiver]

Not entirely true. 4" pcrete/vcrete equal to abt 2" of CaSi or equivalent which is the minimum suggested thickness for high tech insul. 4" of high tech insulation I would agree on diminishing returns but not pcrete. But it also depends on what you want to do with your oven. Pizza one night or long term multiday cooking.

[aaronpizza]

DavidS a question please. Am I right in thinking that instead of foamglas and casi I can create an insulation layer using a vermicrete mix for underneath the fire brick floor? My hearth will be poured next Tuesday and just thinking about acquiring the next set of materials. I know plenty of people use the foamglas and casi - I’m guessing because it’s a cleaner finish (easier to level)?

I am going to do the 4 inch of V.crete myself the casi board is far too expensive!

Over 4 inches has diminishing returns - So I've read

[UtahBeehiver]

Up to you and budget. P or Vcrete requires abt double the thickness for the same K value but quite a bit less expensive than high tech insulation (CaSi/AlSi/FoamGlas) also foamglas will not absorb or transmit water.Do search and research blog.

[Mullster]

DavidS a question please. Am I right in thinking that instead of foamglas and casi I can create an insulation layer using a vermicrete mix for underneath the fire brick floor? My hearth will be poured next Tuesday and just thinking about acquiring the next set of materials. I know plenty of people use the foamglas and casi - I’m guessing because it’s a cleaner finish (easier to level)?

[Mullster]

Cool!

Note that you'll be pouring several hundreds of kilo's of concrete, so make sure the woodwork structures is sturdy enough to carry, let's say 10 people.

Plastic film is common when pouring floor-slabs, because the soil will draw a lot of water. This construction won't draw as much. You can use plastic, but note that any wrinkles will make impressions in your concrete.

Thinking I’ll only put plastic on the bottom then and not up the sides of the frame

[Mullster]

Kvanbael just found a weight calculator - looks like approx 477kg - so maybe 6 people

[Mullster]

Kvanbael you've got me wondering about the weight - think I’ll do some reinforcements!

[Kvanbael]

Cool!

Note that you'll be pouring several hundreds of kilo's of concrete, so make sure the woodwork structures is sturdy enough to carry, let's say 10 people.

Plastic film is common when pouring floor-slabs, because the soil will draw a lot of water. This construction won't draw as much. You can use plastic, but note that any wrinkles will make impressions in your concrete.

[Mullster]

Really feeling awesome about this project now! Back to woodwork today (which is my favourite) framing out the stand and getting ready for the concrete hearth pour. Found it quick work today. I still have the outer frame to make but have the materials ready for that.
realised that by putting a layer of plastic down before the pour not only will it help the concrete set harder (according to the advice I’ve read on here) but also will mean any gaps around the frame on the inside won’t matter.
I’ve deliberately set my boards slightly below the level of the walls so that the hearth ‘sets’ that middle wall which creates my 2 storage compartments in place.

[Mullster]

Some good progress today - managed to finish the stand ready for shuttering (I think that’s the right term?). I think my stand could have been a touch straighter and my mortaring skills definitely need some work - but it all seems solid - and it feels like the hearth will forgive little imperfections. Plus rendering the stand later will also hide any off bits.
Looking forward to the next stages!

[UtahBeehiver]

Powdered clay. Try where Brickie go to get there supplies. Sometimes pottery shops will carry it at a premium price