Homebrew cast oven UK Build

[columbiers]

Hi,
Building a cast oven in the UK, casting using 3:1:1:1 homebrew mix. Not using the steel needles to keep costs down. Going to cast in one piece, hoping for as few cracks as possible. Was originally planning clay but gone for this in the hope it's longer lasting. 100mm refactory layer, 100mm insulation layer, sand/cement render, masonry paint. Hoping to not need a roof.

100mm slab with rebar has been cast, base out of blocks to be built tomorrow. Floor will be perlite/cement mix, topped with 64mm firebrick

[SableSprings]

How deep is your base perlcrete layer? You should be thinking about a 5:1 mix (perlite:cement) about 10-13 cm deep (4"-5"). Most of the cast ovens run about 5-7 cm thick, so your 10 cm shell is thicker than you need. From what I've read, if you want to keep costs down and keep "shell cracking" down to a minimum, you'd be better off using the stainless steel needles and a thinner (10-12) shell since the stainless needles help prevent cracking of the refractory material.

As I noted in your other thread, David S is our resident expert in casting and I think he'll weigh in here to help with his hands-on experience. You might also think about drilling some small holes through the base cement of the floor, so you'll get some added "drainage" for the floor insulation perlcrete. Also, if you are not going to be under cover you'll want to make sure to think about a water dam around the perimeter of the cast dome. This is needed to prevent water from penetrating into the base layer at that base interface.

Looking forward to your build...as are you I'm sure

[columbiers]

Perlite base is 100mm thick.I can add a roof if needed, I'll investigate a dam as well though.
Issue with needles is sourcing them at a realistic price in Uk, so far I've only found 20kg at £150 +shipping. I'll look at a thinner shell with buying needles to see if costs will balance out, I'm already at the top end of the budget.

[UtahBeehiver]

I second that you review David S threads or PM him casting ovens. He is also an advocate of SS needles. I did a quick Google search and found a site that sell SS needles by the kg. I can't recall for sure but I think the amount required is 3-5%.

http://www.castreekilns.co.uk/stainl...ory-3234-p.asp

[fox]

with needles is sourcing them at a realistic price in Uk, so far I've only found 20kg at £150 +shipping. I'll look at a thinner shell with buying needles to see if costs will balance out, I'm already at the top end of the budget.

That sounds like a good price, I pay £10 kg.
How big is your oven going to be? 100 mm is pretty thick for a cast oven, I cast mine at 60mm & I add the needles @ 50g per 25kg bag of refractory. So I use around 2kg of needles for my 32" domes.

[david s]

That sounds like a good price, I pay £10 kg.
How big is your oven going to be? 100 mm is pretty thick for a cast oven, I cast mine at 60mm & I add the needles @ 50g per 25kg bag of refractory. So I use around 2kg of needles for my 32" domes.

The recommended addition of stainless fibres is a minimum of 2% by weight of dry material. 50g/ 25 kg is nowhere near that figure. It should be at least 500 g

[columbiers]

That sounds like a good price, I pay £10 kg.
How big is your oven going to be? 100 mm is pretty thick for a cast oven, I cast mine at 60mm & I add the needles @ 50g per 25kg bag of refractory. So I use around 2kg of needles for my 32" domes.

It is a good price, but I don't want that many. Oven is 90cm (35"), I've worked out I need around 10kg. I was casting at 100mm under the idea that thicker would be better?

[fox]

The recommended addition of stainless fibres is a minimum of 2% by weight of dry material. 50g/ 25 kg is nowhere near that figure. It should be at least 500 g

Yes, sorry that was a terribly rushed post that I did not explain very well & also seems to be missing several lines of info & several mistakes!

The 25kg bags of refractory mix I buy, already has added needles but there does not seem to be that many & they are quite short so I add a further 250g (not 50g) of longer needles per bag.

I use 8 bags to cast my 32" domes & entry and I add a total of 2 kg of extra needles, so if I was adding at 2% that would be 4kg of needles.

[columbiers]

Progress has been made, base is built, dense blocks used. Not the neatest laying but it is strong.
Built a brick enclosure on top that will receive perlite/cement mix tomorrow that will then be left to dry out for 2 to 3 weeks. Probably render the lower half while it's drying, also want to get a food prep area up.

I've managed to get 5kg of the needles, thats all they have. Going with a dome/entry of 70mm thick, I'm calculating that at around 200kg. So 5kg would give me needles at 2.5%, perfect!

[columbiers]

Vermicrete layer in place, 100mm thick.
Base rendered, painted with masonry paint.

Next step firebricks on the floor, sand/clay to level. Got storage heater bricks for this part. Hoping to get first pizza out by June!

[columbiers]

Triple update, lots done over last few days:

Firebricks down and level, brick arch complete. Arch was a pain to do, certainly justified my decision not to go for a brick build, I lack the patience!

[columbiers]

Sand former built, used blocks under to reduce amount of sand used, was still a lot. Sand will be reused as render later on. Paint can is there to create hole for the flue

[columbiers]

Dome is cast:
Used homebrew 3:1:1:1 Sharp sand, Lime, Fireclay, cement, 2% needles.
Mixed nice and easy- mixed dry first, then water, then needles last. Wore decent workgloves and mixed by hand- only 2 jabs from needles. Considered using my cement mixer but decided to do it in the barrow and went well.
Managed to pick hottest May holiday on record for the UK to cast it- worked fast and kept spraying it down with the hose. It's now curing nicely, will spray it again. Didn't bother making particularly smooth as it'll be covered by 5cm layer of perlite/cement mix. Probably give it a week before that goes on, going to remove the sand and blocks in a couple days.

[UtahBeehiver]

By to looks of the pics I do not see a vent/chimney anywhere and no room out front. What are your plans on this?

[columbiers]

There's a hole for it, top at the front, not clear on pics. There's a paint can in one pic which I cast around then removed, it's left a 150mm hole. Plan is twin wall flue, in stainless. Probably metre high.