Castable refractory

[stonecutter]

Re: Castable refractory

There is more than one sort of Portland Cement available in Oz.
Leaving out rapid-set, sulphate resistant, high early strength, the special white stuff for making nice white mortar, etc, there are two types that you might be offered if you roll up to the hardware store and say "give us a bag of cement, mate".

Type GP is the everday Ordinary Portland Cement.

Adelaide Brighton's FAQ page says Type GB is Portland Cement blended with 30% ground granulated blast furnace slag.

So, the question: is Type GB, containing a cementitious substance other than OPC, a slightly better choice for the cement portion of the homebrew mortar?
Opinions, anyone?

Sure, the mineral content of the slag is refractory material. I would say it would be a better choice because if that.

[david s]

Re: Castable refractory

A couple of things to add.
1. Polypropylene rope chopped into strands may not work like the fibres dedicated for the purpose. They are really fine (finer than hair) and melt at 160 C polypropylene rope is probably much coarser and just because its polypropylene doesn't mean it wil melt at the same temp. Suggest you test it.
2.The alkalinity in concrete may provide good resistance to corrosion, but that is for ambient temps. Any reaction is sped up with heat usually, rust certainly is. That, presumably is part of the reason why stainless steel needles are the recommended reinforcement.
3. Hydraulic lime is the preferred choice rather than its poorer cousin hydrated lime, but it is really hard to get in Australia, let me know anyone who can tell me where to get it.

[david s]

Re: Castable refractory

Sure, the mineral content of the slag is refractory material. I would say it would be a better choice because if that.

Haven't heard of GB. The choice I have is GP or Builders cement which has more fly ash which improves its viscosity marginally for pouring slabs, although I use a super plasticiser for this.

[tdibratt]

Re: Castable refractory

Interesting posts on mold options. Can you point me to any pics on the forum of these molds so I can visualize.

Thx

[wotavidone]

Re: Castable refractory

Haven't heard of GB. The choice I have is GP or Builders cement which has more fly ash which improves its viscosity marginally for pouring slabs, although I use a super plasticiser for this.

In your part of the world GB might be called Premium or Blended cement.

[wotavidone]

Re: Castable refractory

The other thing I've noticed is that cement production and use seems very localised in Oz. To a certain extent local producers make cement from local materials and sell locally. I guess cement is heavy and freight costs hurt. So type GB might simply not be made in Queensland. A cement manufacturer in Queensland would probably have to go all the way to Mount Isa to get the slag which would cost, I imagine.
Here in South Oz, Adelaide Brighton Cement only have to haul slag 230 km from Port Pirie.

[david s]

Re: Castable refractory

Hey Mick,

How is that small cast oven coming along?

[wotavidone]

Re: Castable refractory

Not coming along at all, unfortunately.
I've scored some free plywood with which to make the mould. #2 son told me about his boss's giant pile of unwanted solar panel pallets, and I picked up some free single use pallets.
This week I expect to start my mates brick oven. After that, maybe.

This interesting link was posted on the uk wood fired ovens forum.

howjunction.com/2022/in-the-garden/how-to-build-a-free-form-bread-oven-1/

The builder used 1 cement, 1 fireclay, 2 lime, 9 sand.

[wotavidone]

Re: Castable refractory

Received a call from the blast furnace metallurgist from work. "wife's car broke down, can you give us a hand."
He came around to collect me. I was firing the oven to make pizza and ook ook.
Conversation about refractory mortar ensued. "obviously not CR90," he said, "wrong colour".
"high temp refractories wouldn't work, they wouldn't get hot enough to build the bonds," he said.
I told him what the homebrew is. " Good as any, it's when they cool down that they crack, cool it as slow as possible," he said.
We were looking at 500 degrees on the dome. "Right in that range where nothing works properly," he said, "What time is dinner?"

[cnegrelli]

Re: Castable refractory

Not coming along at all, unfortunately.
I've scored some free plywood with which to make the mould. #2 son told me about his boss's giant pile of unwanted solar panel pallets, and I picked up some free single use pallets.
This week I expect to start my mates brick oven. After that, maybe.

This interesting link was posted on the uk wood fired ovens forum.

howjunction.com/2022/in-the-garden/how-to-build-a-free-form-bread-oven-1/

The builder used 1 cement, 1 fireclay, 2 lime, 9 sand.

What do the experts think of that link and mix?

[hurkinite]

Re: Castable refractory

Has anybody used foam insulation board for a mold? You have to get the dense purple kind and not the white kind with the little beads. But it can be shaped with hand tools and sanded to a super smooth surface. I have used it with a vacuum bag to make interesting curves in skateboards. Seems like it would be easier than trying to get smooth even curves in plywood.