Homebrew castable build, Newcastle UK

[mesoiam]

Hello again. Unfortunately my thread was lost in the great hacking of 2020.
Anyway, I'm currently building a homebrew castable oven in Newcastle in the North East of England. I'm going for an 800mm ID dome, 50mm thick. I've had some advice from UtahBeehiver and where we left off I was going to check the specs of the CaSi Boards. I've since had the techspec from the helpful folks at Kilnlinings.co.uk, I can recommend the service there for anyone building in the UK.

Compressive strength is listed as 2.6MPa (377 PSI), can't remember what was suggested but it sounds high enough.
Thermal Conductivity:
@200 DegC 0.08 W/(mk)
@400 DegC 0.10 W/(mk)
@600 DegC 0.12 W/(mk)

My firebricks, calcium silicate board, fire blanket and fireclay have just arrived. Looking forward to laying out some bricks for cutting this weekend.
Still need to get sand and mortar but all the tricky things are either here already or on their way.
I may be spending some time outside B&Q in a socially distant queue this weekend but I'll be thinking about the nice things I can cook when it's all done.

Thanks everyone so far for their help (now unfortunately deleted)

[aaronpizza]

Looks great - I'm about a week ahead of you on my build so I'll be watching this closely

[mesoiam]

Yes I've seen yours and Mullsters posts around, watching intently also. Will post progress pics if I make any progress!

[mesoiam]

Progress update: Cutting the firebricks at an angle for the herringbone pattern. The bricks are rated for over 1400 degrees, so the 45 degree cut was no problem.
Used a diamond disc which went through the firebrick easily, only a small grinder so cut from both sides. I identified the less perfect side and drove a chisel in, leaving the top with a nicely cut edge. I cleared up any overhang of the inner part with the grinder so they would sit nicely against the front bricks. It's only a couple of bricks, but it was exciting to see how the oven floor will look.

[UtahBeehiver]

Dry cutting fire brick produces a lot of silica so be sure to were proper PPE.

[mesoiam]

Yes indeed, cant be too careful.

In other news I've found it impossible to find stainless needles. I have some non-stainless needles on the way, the supplier says they have supplied to pizza ovens before, even mobile ones, and refractory made with these is used in incinerators etc. Could I ask the opinion here of the experienced members, are the non-stainless needles better than nothing or worse than nothing? I will be adding polypropylene fibres to the homebrew mix also. If anyone has a UK supplier who can supply small quantities I'd be very grateful.

Thanks for any help, and thanks already for the help so far.

[david s]

The correct name for them is melt extract fibres, that may help your search. They are the recommended reinforcement for castable refractory, thin to increase surface area so they can dissipate their heat without creating expansion problems and stainless so they won’t corrode. It is the fine burnout fibres that are more important. Most manufacturers don’t add the melt extract fibres because they’re expensive and a bitch to work with so don’t worry if you can’t get them. If it were me I wouldn’t be using non stainless steel fibres as heat accelerates corrosion reactions and any rusting increases steel in volume producing more cracking problems. Try asking on the ukwoodfiredoven forum.

[mesoiam]

Could've sworn I replied already, I must've got sidetracked.

Thanks David, I think I'll just leave them out and cure extra carefully.

Today's update: forged ahead and got the Calcium Silicate board cut into a keyhole shape, and poured the vermicrete slab (5:1 vermiculite and portland cement).

Edit: I'm not sure what's happening with photos, they are being resized to 83x111. Not sure if it related to the forum reset. Maybe I need to see about putting them on imgur or something.
.

[Mullster]

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

[UtahBeehiver]

Pictures can be up to about 1.25 mg and somewhere around 4-5 per post.

[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

[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.

[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

[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.

[mesoiam]

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