Homebrew castable build, Newcastle UK

[Robarb]

Nice pics!

As i will be undertaking my own castable, i would like to understand what is the reasoning behind casting the 'entrance, or gallery opening separately?

Can normal, dense bricks be laid here to form a curved archway?

Thanks

[UtahBeehiver]

Nice work, one of the nicer cast I have seen. Now you have to be realllllyyyy patient. You have a lot of water in your oven between the dense cast and vcrete, It is going to take several weeks to dry and even consider any type of cure fire.

[Nick J C]

Work of art, that sand castle.... I am planning on doing the same with the quadrant template and post in the middle. Good luck with the gallery.... I am itching to get my dome cast, but vitcas delivery with all the stuff delayed - apparently Im not the only one building a pizza oven and they are short on stock!

[mesoiam]

Hello again, so I've been busy.
I made a door mould by cutting a piece of wood from an old drawer and curving a piece of hardboard over it. It ended up very strong once it was tacked down.
You can't see it here but there is an upright stick right in the middle of the dome to set the height (400mm radius),it has a screw head sticking out slightly so i can feel where it is when there's sand everywhere, the stick is just screwed to a small piece of plywood and then I built bricks around it to anchor it in place.
I used bricks to take as much volume as possible but even with that it took much more sand than I expected to form the dome, needed another run to b&q as I didn't want to be short of sand for the actual casting. If I was doing this again I'd buy a dumpy bag rather than many many bags of sand.
When I was marking out the oven floor I was beginning to think the oven was disappointingly small, but once I saw the mould in 3D it seemed quite big.
I made a quarter circle guide to help shape the sand, just touch the top part to the aforementioned screw at the very top and then shimmy the sand out of the way until I can get the bottom part to touch the oven floor, worked well. The mould was then covered in wet newspaper, a squirty bottle of water was useful for this.The newpaper didn't want to stick to the sand as I imagined, but it sticks to itself readily, so I started by draping pieces over the top and working down from there.
I then covered it in a wet bed sheet to keep it wet until casting day.
For the casting I made the homebrew 3:1:1:1 (Sand, cement, lime, fireclay). I thought I'd list the ingredients for anyone reading as many posts mention the ratio and assume knowledge of the ingredients.
I weighed out a test batch on the kitchen scales, 3 litre sand, 1 litre sand etc. I used this to estimate how much stainless steel needles (melt extract fibres) to add. It ended up being roughly 100ml of needles on this test batch to make 2.5% of the dry weight.
I mixed up the batch and went to work, I was originally thinking I'd use a trowel because the stuff is filled with sharp bits of steel, but it's so claggy it's easier to just use hands with gloves. I did't get poked with needles in the end so that was fine.I cut a little piece of wood to set the thickness to 50mm, it ended up a little bit thicker than that but definitely no thinner.
I continued with the same batch size the whole way through, probably could have been a bit faster otherwise, but seeing as it was working I didn't want to change it up, the stuff does go off fast. I should mention it was a nice cool day which I think is fortunate for the working time of the casting.
I've got the day off specifically to make the chimney gallery so I best get to it.
Thanks all for the interest and Utah and DavidS for the advice.

edit: I forgot to mention also added polypropylene fibres, one annoyance with these is that they all came clumped together and needed a few minutes to fluff them up and distribute them in the mix. They remind me of thistle seeds

[Robarb]

How much further have you got with this? I'm very intrigued

[mesoiam]

Cheers, keep your photos coming too so I can copy!

[Mullster]

mesoiam This is really helpful to me to see these pictures - I had been struggling to see what people meant by the wedge shaped breaks at the vent/flue area.

[mesoiam]

Yeah I've got some CaSi scraps, plugging the ends sounds like a good plan thanks. I went off the idea of sculpting wedge shapes for the whole length, as the cuts are not perfect.

[UtahBeehiver]

You have any scrap CaSi board that you to fill the wedge cavity? Maybe even a lean vcrete, 8-10 to 1. Dry V you need to be able to hold in place or even plug ends with so CaSi scraps

[mesoiam]

Floor is shaping up. Cutting the bricks with a bolster as these edges will not be seen. I've cut a wedge out of the underside of the front bricks to help reduce the amount of heat lost out the front. Will probably fill this void with dry vermiculite before casting.

[mesoiam]

Nice one thanks. I'll cast in two parts then.

[david s]

I believe the primary function of leaving a gap is that it can act as a thermal expansion joint so when the inner oven parts heat and expand they won’t be putting pressure on the outer parts reducing the possibility of cracks. It’s secondary function is to reduce heat travel via conduction. Placing a highly conductive and rigid material like stainless steel in the space only encourages heat transfer and doesn’t allow any flexibility but it does look pretty. The wedge shape idea is a good one IMO. I fill the gap with some blanket and seal off the top 1/4” or so with 4:1 vermicrete which is weak enough to still be compressible. I’ve tried all kinds of fireproof caulks but none of them seemed to work any better than the 4:1 vermicrete.

[UtahBeehiver]

1. Thermal breaks are always a debatable topic. If you have the means to do it without much effort or expense then have at it. I installed them on my oven and does it make a difference, beats me. But I did do something similar to the wedge shape you talked about but on my arch, see pic. Also install a ss retangular tube filled with CaSi board between dome and vent brick. I believe David S leaves an air gap filled with vcrete. You need to check with David on one piece but if I remember right he suggest a two piece process to eliminate expansion issue

[mesoiam]

Hi, I've got another couple of questions if folks don't mind. I'm laying out my brick pattern for the floor, I've seen heat breaks mentioned so that got me thinking a bit more before I continue this weekend.
1. Is it OK for the firebrick to continue all the way to the front of the flue chamber or do you think I should add some sort of thermal break between the main dome bricks and the entrance to prevent heat loss?
The cast oven by the sea had the front bricks cut to a wedge shape underneath to reduce conductivity, could maybe do something like that. Thoughts?

2. Is it OK to cast the oven and flue gallery in one piece or would an expansion gap be recommended between them, if so, what material to join with, 5:1 vermicrete? Stainless needles have now arrived so hopefully my castable will be quite sturdy.

Thanks as always for all the wisdom on this forum.

Edit: I should probably mention for clarity that all the inner floor bricks will be cut back so that they end just beyond the outside edge of the cast dome. They will still have a layer of blanket and vcrete insulation outside them. My question is for the doorway bricks which will reach all the way to the front.

[mesoiam]

Looking really good! I love the brickwork on the stand - gonna be a good looking oven!

Very kind of you, it took me about a year :-D