Castable oven

[julian]

Hi everyone.

I haven’t posted for 10 years, as life has seen a lot of moving around the country for the past few years. The last time I built an oven was on a very tight budget at a rental.
We have bought a house in Adelaide and have built the dream workshop- 60 square metres with heaps of storage.
Several family members have expressed an interest over the past decade since I built my last oven but no one has tackled this.

To this end I ended up buying a very nice and proven heavy duty fibreglass mould for ovens with an inner and outer skin. The bloke that made it refined it over many builds and actually made the ovens by filling the outer mould with a vermiculite/perlite insulating mix then pouring in a refractory layer which sets against the inner mould. The dome is made to cast in two parts and with a seperate mould for the mouth of the oven and then mortared together on a prepared base.

The mould makes an oven of 60cm internal diameter with a good design and good aspect ratio.

The expense was significant, but I think justifiable given how many will ultimately be made.

Has anyone seen a similar method that prepares the two layers at once?

I need a refractory that can be poured as a slurry to fill the void, and would need some advice as to an appropriate product. I don’t mind buying in bulk. I’ve read extensively here and would prefer a true castable not based on GP cement as will be making for others. Can anyone here help with some advice on products and approximate costs?

I’ll post photos later.

Thanks.

[UtahBeehiver]

David S of Townsville, Queensland is our casting expert on the forum. Reach out to him.

[julian]

Thanks Russell, I was hoping engage him here as I can’t find the specific information that I’m after despite extensive searching. Hopefully David S will pop up soon.

[fox]

I would like to see some pictures, I use a fibreglass mould but apply ceramic blanket as insulation.
The refactory cement I use works far better as a dry mix, I don’t know of any purpose refactory cements that is designed to be applied wet.
I had to invest in a decent vibrating table and a vibrating poker to get the best from my mould, my first attempts worked ok but now by useing a very dry mix and the vibrating tools, I am achieving extreamly good results.

[david s]

Hi everyone.

I haven’t posted for 10 years, as life has seen a lot of moving around the country for the past few years. The last time I built an oven was on a very tight budget at a rental.
We have bought a house in Adelaide and have built the dream workshop- 60 square metres with heaps of storage.
Several family members have expressed an interest over the past decade since I built my last oven but no one has tackled this.

To this end I ended up buying a very nice and proven heavy duty fibreglass mould for ovens with an inner and outer skin. The bloke that made it refined it over many builds and actually made the ovens by filling the outer mould with a vermiculite/perlite insulating mix then pouring in a refractory layer which sets against the inner mould. The dome is made to cast in two parts and with a seperate mould for the mouth of the oven and then mortared together on a prepared base.

The mould makes an oven of 60cm internal diameter with a good design and good aspect ratio.

The expense was significant, but I think justifiable given how many will ultimately be made.

Has anyone seen a similar method that prepares the two layers at once?

I need a refractory that can be poured as a slurry to fill the void, and would need some advice as to an appropriate product. I don’t mind buying in bulk. I’ve read extensively here and would prefer a true castable not based on GP cement as will be making for others. Can anyone here help with some advice on products and approximate costs?

I’ll post photos later.

Thanks.

I also use a fibreglass mould, but use ceramic fibre blanket outside itthen a layer of vermicrete outside that, then finally a cement rendered outer shell. The fibreglass does take quite a beating and I find requires some maintenance about every 10 castings or so. A steel mould would actually be better, but harder to fabricate.
Before the current (exonerated as a class 2 carcinogen) generation of blanket became mainstream it was too expensive so I only used vermicrete and found some drawbacks. Being less flexible than blanket and having the property of swelling if heated when still wet, I cracked a couple of outer shells by applying heat too soon. The damp vermicrete being in direct contact with the inner dense castable is a problem. Having a blanket layer between the inner dome and the vermicrete layer works much better IMO, the blanket being dry and somewhat flexible acts like an expansion joint.
If I were building an oven for myself I’d use homebrew castable but if you are making ovens commercially then castable refractory is a better choice to avoid warranty issues. Be careful the stuff is very temperature dependent (I use chilled water in the hot months) and also very sensitive to superplasticizer (easy to overdo it and get separation)
Regarding vibration I built my own vibrating table that sits on cylinder head valve springs. Cheap to build and very effective.

[david s]

I would like to see some pictures, I use a fibreglass mould but apply ceramic blanket as insulation.
The refactory cement I use works far better as a dry mix, I don’t know of any purpose refactory cements that is designed to be applied wet.
I had to invest in a decent vibrating table and a vibrating poker to get the best from my mould, my first attempts worked ok but now by useing a very dry mix and the vibrating tools, I am achieving extreamly good results.

I don’t understand how your product works if packed in dry as castable refractories require water for the hydration process. Many of the products, and there are lot, are designed for gunning where the dry castable and water are mixed at the nozzle. Using this method of application it is extremely difficult if not impossible to attain a measured ratio of water to dry material. I’ve found that making the mix to manufacturers water ratios results in a mix that is not wet enough and more likely to contain voids. The “ball up” consistency I find works well and can be made more fluid with small additions of superplasticizer.

[fox]

I have found mixing as the manaufacturers recommendations results in a vert tight and void free result but it must be properly vibrated.
The mix feels and looks very dry (3-4liters of water per 25kg) and sets very quickly.
I mix in a small cement mixer and use a 48” vibrating table, the mix sinks dramatically and a surprising amount of the water rises to the surface.
I have found useing more water makes the mix much more user friendly but results in a softer end result, it is quite easy to scratch the surface with a nail for instance, but with a drier mix the surface is rock hard and smooth.

[david s]

“”The refactory cement I use works far better as a dry mix”,”

Sorry, I interpreted this as using no water, but I see that’s not what you meant.