Heat resistant mortar - hydraulic or ceramic drying??

[Breven]

Frances-
Can't help with with your motar question. I mixed my own using fine sand, portland cement, and fireclay. Seems to be workign great. As far as your question about your dome colapsing if it rains- I don't think so, as long as you do a full course and don't leave the course half complete. The laws of gravity and the 2,000 year old arch design (which is the basis of a dome shape) won't allow the bricks to colapes as long as they are wedged together in a circle tightly. Unless your mortar completley breaks down in water.

[aureole]

Sorry, it was me resurrecting an old post: Frances finished his build a while ago (and hasn't AFAIK, fallen down!) - mine is still very much an ongoing project!

[Breven]

Well, I guess the heat cured mortar works.
Are your pics current? Looks like you're about ready to start the floor and dome eh?

[aureole]

Yeah: I'm all ready to go. Hopefully going to order the bits today, and get them soon so I can go make the dome as soon as the english weather sorts itself out!

From my scraping of the forums, I think it's the case that Hendo and Frances have definitely used the heat-drying wet stuff. I think other UK builders have used a fireclay and lime mortar. I'm going to get 60 kilos of fireclay and 100 of air drying wet-mix mortar and have every angle covered!

[dmun]

Frances used fireclay-and-sand only mortar (no lime or portland), on the advice of local masons, and it seemed to work out fine.

[aureole]

Ah,

I've got an option b given to me, I've been recommended/suggested: air-drying mortar on the inside of the bricks, followed by some very fine refractory concrete on the outside. The concrete I'm getting has a very fine ballast/aggregrate inside. If this is a stupid idea, I've got the backup plan of 75kg of fireclay on the way. Not sure what I'll do with all the spare refractory stuff!

Quite an interesting conversation with the guy from Midlands refractories: he essentially told me I was completely mad to try this (although he conceded the Romans definitely knew what they were doing, and if ovens survived the volcano at Pompeii, they must've got something right!). He suggested the air-drying stuff is used (very, very thin) because you don't want any joints between refractory bricks.

Interesting stuff, I'm hoping the refractory concrete/cement I get is pretty close to refmix (I'll check the label when it arrives).

[atdabch]

be carefull of the pre-mixed mortars...the ones i found are not water-proof when dry...constant rain and wetness will break them down

[asudavew]

Originally Posted by aureole

Frances finished his build a while ago !

Yeah SHE finished a long time ago!

[Frances]

Hehe, yep definately still female the last time I looked...

Sorry I didn't answer earlier, but we were away for a couple of weeks. Sounds like the mortar I used wasn't the same as what you're talking about at all. Mine was a dry sandlike powder which needed to be mixed with water before use.

Here's another thread where I go on about it at length , and so far it seems to be working just fine! (further long term testing is being undertaken as we speak)

http://www.fornobravo.com/forum/f8/h...clay-2783.html (Heat-dry mortar made of refactory clay and refactory sand (and nothing else))

Oh yes, dvonk has since built an oven with the same sort of product.

[aureole]

Originally Posted by Frances

Hehe, yep definately still female the last time I looked...

Ooops. Sorry about that

It's a funny thing... I've got two options: the fireclay mortar or the superplastic. My current plan is to butter the bricks finely with the superplastic, then use very fine castable concrete mix in the wedges (provided it's workable enough to do that). I'm going to have a play with the materials to check it'll bond well enough and fill the voids.

Anyone have a clue about plasticising compounds at high heats? Is it okay to add them and/or PVA to a high-heat mortar?