Can someone who knows please take a look? (david s)

[jersey bob souvlaki]

Sorry I meant to put someone who knows casting materials in the title,
I'm making a mold right now getting ready to cast an oven. I've got a fair amount of money and time invested in this project and I'd really hate to fail because I made a wrong choice.
I've not been able to find a refractory concrete mix here in Greece especially made for casting. There seems to be some debate about whether the home brew works or not. I was told by the guy I bought my fire bricks from that it definitely would not.
Anyway, this product https://www.isomat.gr/wp-content/upl...at-ak-fire.pdf is readily available. I think it has a density close to what davis s said is suitable. But I haven't been able to find out if the thermal conductivity is good for a cast oven. If someone could take a look and give me an opinion if I would have a better chance of success with this product, I'd be deeply in your debt. thanks, bob.

[david s]

I've never built an oven using the home brew mortar as a castable, although I've recommended it to folk who've used it and reported success. As to how it would stand up long term is another question. The two locals I refer to built theirs around 4 years ago so that's not bad, but I have no idea how often they use their ovens. Undoubtedly your supplier will tell you it won't work if he's trying to sell you his product. Regarding that stuff you linked to, you have to realise that it is a mortar not a castable and is not designed to create a thick casting. However it may work, but you'd be advised to add some burn out fibres to help with water removal, not essential, but helpful.The beauty of the homebrew is that it's so cheap it wouldn't be out of the question to do a rebuild down the track.

Another idea which may suit you better is to use local rock instead of brick and use your isomat mortar to hold it all together. I've seen enough ancient ovens in castles that used rock for their ovens and they've been there a very long time. Haven't been to Thessaloniki, but we were in Paros in 2010 and the ploughed fields there had more rock than soil.

[fox]

I am far from an expert on the matter of castable refractory cement but from what I can gather fire brick is the best overall material to use as a dense inner dome for a WFO.
I bought some commercial dense castable ready mix from a well respecter retailer to cast my dome. It seems, in fact, to be crushed fire brick mixed with high temp cement!
However as I understand it is not quite so simple as crushing fire brick & adding HTC as the ratios are pretty important. The amount of brick dust & brick particle seems to be important as well as the quantity of cement.
The other factor is the product I have bought is really difficult to work with. Not like ordinary concrete but very grainy & dry, not creamy and pliable !
I would imagine it would be very difficult to use over a mould as it would be difficult to compact & shape evenly, I think the end result would be full of air voids?

The home brew often mentioned seems to be very easy to apply over a mould as it has a nice smooth workable texture & does not set as quickly as refractory cement.
In my case I made an inner and outer mould so the mix could be vibrated as I filled the mould but, even then it is not a user friendly product for a first time experience!!!
David suggest using nylon fibres, perhaps S/S pins would help with the integrity as well but they would definitely make it more difficult to work with.

[jersey bob souvlaki]

Thanks for the replies. I've been kind of out of my depth with this but I told the family I could do it. All the info y'all have shared has been a great help. Interesting idea about using local rocks instead of bricks. But that would be stonecutter's area. I'm just an old drywall hanger. Well, I'll press on. Still cutting wire BTW. Trying to think up a machine to do it. Thanks again.