Homebrew Castable 650mm East Sussex UK

[WaterDog]

Hi bamforp. How has your expansion control experiment been working in practice? Now that you’ve completed two ovens using this idea, I’m more than curious. Just beginning my dome and am incorporating this idea as well as it makes a lot of sense.

Thanks for posting, very helpful.

[bamforp]

Hi, I think the experiment worked out pretty well. I do have some cracks propagating up from the floor of the oven but they only get as far as the weak joint rather than propagating a full 180 deg across the dome. I have attached some photos from the two ovens that hopefully illustrate what I mean. Given that it's easy to add the weak joint I think it's worth the effort and it certainly has not adversely impacted the integrity of the dome.

[david s]

That's most intersting. I made exactly the same obsevation in my one piece dome casting that's now 16 years old and fires as good as new. A very fine hairline crack running all the way around. I thought if that's where you want to be that's where I'll engineer my join for a three sectioned cast build in future. With heat rising by convection a faily large section is going to get way hotter and faster than any other oven part and the resulting thermal expansion problems can be releved at this very position.

[WaterDog]

Thanks bamforp (and David). Nice to see it did follow the path you created. I’m sure it prevented more random cracks. I’m incorporating your idea into my dome build this week. Will post images once it’s done and fired up to temps after it’s dried out enough.

[geoff7877]

bamforp Beautiful oven! You and WaterDog have chimed on my thread about my upcoming build and offered some great advise. Thank you both!

Love the expansion joint around the top. I’m definitely going to incorporate that in my oven and thinking of using that method to create my dome in 3 separate sections to allow for the inevitable cracks from the floor up like david s mentioned. Seems like it would not be difficult to do using your newspaper method.

I’m curious about the drains that you built into the gallery. Is that recommended more for your style oven? Mine is going to be an igloo shape so I’m curious if drains are recommended for that style oven. Also, have you seen any issues with cracks around the flue where it’s cemented into the gallery? That’s a spot where my current oven cracked so I’m curious of how to attach the flue to allow for expansion.

Thank you

[bamforp]

The holes in the flue gallery are there to vent the insulation layer in case any moisture gets trapped between the refractory and the outer vermicrete layer. I've seen some people use a mushroom vent at the apex of the vermicrete layer to achieve the same thing.

I've not had any issues with cracks in the flue so far but I cast the dome and flue separately and I think I used the same newspaper technique to create a weak joint between the two parts.

In hindsight I should probably have stressed a bit less about cracks in general. I think they are pretty much unavoidable but the dome structure is inherently stable so unless things go really badly wrong the cracks don't interfere with the enjoyment of the oven.

[geoff7877]

bamforp What was your total amount of materials needed to make the home brew for your oven? I get the 3-1-1-1 breakdown, but how much of each material did you have to buy to build the dome and gallery? And how thick is the dome?

Thank you.

[bamforp]

geoff7877 My dome cast was nominally 50mm thick. I used the homebrew calculator put together by 4stroker to estimate quantities but I cannot remember the exact amounts I ended up using. Of the materials that I had to source online, I know I only used 1 x 25kg bag of fire clay, 2 x 100L bags of vermiculite (I used a lot of vermicrete to get the overall shape I was after) and 0.5kg of AR fibres and 0.5kg polypropylene fibres (both of which I had loads left over). The sand, cement and lime are readily available locally so I would have just picked up what I needed on my next trip into town. The most expensive materials were the firebricks so it is worth spending a bit of time working out your desired layout and ordering only what you need unless you can get them locally.