Ciment Fondu / Refractory Castable Question

[di11on]

Hi folks,

I'm looking to build a small oven (22") and from my research so far, it seems that using a castable refractory would be the most efficient way to go in terms of price and performance for a given external diameter and weight.

I'm living in France and am really struggling with the translation of many of the terms.

Anyway, I have come across the product Ciment Fondu (link in French: CIMENT FONDU?). They sell this as being suitable as a mortar and a concrete, depending on what you mix it with and specifically say it's suitable for "pizza ovens".

It suggests mixing it with grog/chamotte though, which I'm finding very difficult to find. I can only find one link where it's costing €75 for 50kg which rules this out as an option on price grounds straight away. Can I mix it with something else? If so, what?

I'm also struggling with the precise definition of grog/chamotte. What is it?

In the end of the day, I'm looking for recommendations on specific materials to make a good castable refractory for a reasonable price for a small oven :-)

The link gives temperature ratings for different aggregates as follows:

Temperature
Limestone sand 450 ? C
Siliceous 500 ? C
Alag ? 1100 ? C
Chamotte 1200 ? C

I'm guessing from this that if I mix it with normal aggregates, it will only be good for 500 degrees at best?

Anyone any insight suggestions here?

I'd like to keep the price low. This oven will be simple and will be designed to be moved as we're in a rental property so it won't need to last forever.

[Tscarborough]

Re: Ciment Fondu / Refractory Castable Question

Grog is crushed brick, normally refractory brick for this application. 22" is tiny, you might consider adding at least a couple of inches. Stay away from limestone and silica aggregates in your castable and keep the maximum aggregate size down to less than 1/4 (1/8 is better) of the planned thickness.

[david s]

Re: Ciment Fondu / Refractory Castable Question

Making your own castable mix is fraught with problems. You may not get your proportions correct, you may end up using unsuitable aggregates and you may end up with an unworkable mix that will make placement difficult or impossible. If you are making a small oven it would be a better plan to use what is known in the trade as castable refractory. This is a proprietary mix that contains all the right ingredients in the correct proportions including burn out fibres for better water elimination.
The product is readily available from refractory suppliers. If you want to go the cheap route then try the home-brew mix to make your own castable i.e. 3:1:1:1 sand, portland cement, clay, lime

[di11on]

Re: Ciment Fondu / Refractory Castable Question

Making your own castable mix is fraught with problems. You may not get your proportions correct, you may end up using unsuitable aggregates and you may end up with an unworkable mix that will make placement difficult or impossible. If you are making a small oven it would be a better plan to use what is known in the trade as castable refractory. This is a proprietary mix that contains all the right ingredients in the correct proportions including burn out fibres for better water elimination.
The product is readily available from refractory suppliers. If you want to go the cheap route then try the home-brew mix to make your own castable i.e. 3:1:1:1 sand, portland cement, clay, lime

Many thanks for the reply.

Access to materials is proving difficult... and language issues don't help. I understood that the ciment fondu was something designed for this purpose... i.e. the "fondu" bit meaning that it's supposed to be workable? Would using this ciment fondu instead of the portland cement be a better option?

I've been reading on the French forums (which appear to be more focussed on Bread making than pizza making) and some people go down the route of casting their dome in sections rather than one piece - this might be an option to consider as it may reduce the risk of cracking.

The major problem right now is identifying the materials to use. I may end up going down the home brew route just because I know what the various elements are here in France and where to get them (mostly).

Incidentally, there doesn't appear to be to be much difference between the home brew and the first layer of a cob style oven which is just clay and sand. Considering most people usually add some cement even for a cob oven, the only difference appears to be lime and perhaps more cement?

Incidentally, what exactly is the clay in the home brew mix? Powdered clay?

[stonecutter]

Re: Ciment Fondu / Refractory Castable Question

Where in south France are you?

[di11on]

Re: Ciment Fondu / Refractory Castable Question

Where in south France are you?

Near Nimes, in the south.

[di11on]

Re: Ciment Fondu / Refractory Castable Question

This post seems to suggest that Ciment Fondue is an alternative to homebrew, or rather that homebrew is an alternative to Ciment Fondue.

So, how do you use ciment fondue, what do you add it to?

Fireclay costs me ?23 for a 25kg bag (assuming the powdered clay that the pottery suppliers are offering me is ok) and ciment fondu costs me the same... so it doesn't appear to me that I'm saving anything going down the homebrew route.

[david s]

Re: Ciment Fondu / Refractory Castable Question

Many thanks for the reply.

Access to materials is proving difficult... and language issues don't help. I understood that the ciment fondu was something designed for this purpose... i.e. the "fondu" bit meaning that it's supposed to be workable? Would using this ciment fondu instead of the portland cement be a better option?

I've been reading on the French forums (which appear to be more focussed on Bread making than pizza making) and some people go down the route of casting their dome in sections rather than one piece - this might be an option to consider as it may reduce the risk of cracking.

The major problem right now is identifying the materials to use. I may end up going down the home brew route just because I know what the various elements are here in France and where to get them (mostly).



Incidentally, there doesn't appear to be to be much difference between the home brew and the first layer of a cob style oven which is just clay and sand. Considering most people usually add some cement even for a cob oven, the only difference appears to be lime and perhaps more cement?

Incidentally, what exactly is the clay in the home brew mix? Powdered clay?

Do not replace the portland cement with fondu if following the home-brew recipe. Calcium aluminate cements (fondu) go off very quickly. In the summer I have to add chilled water to slow down the reaction. If you use it in conjunction with lime the reaction takes place even faster, (unlike with Portland which slows down the reaction). With a Fondu and lime mix you would not have time to place the mix because it will start to go off as soon as you've finished mixing it and by the time you get to the bottom of the batch it will be too hard to place. This is part of the reason I advised a proprietary castable refractory instead.
For the temperatures we fire to I believe any powdered clay should be ok. The cheapest source apart from digging, drying, pulverising and sieving your own free clay is bricklayers clay

[di11on]

Re: Ciment Fondu / Refractory Castable Question

Do not replace the portland cement with fondu if following the home-brew recipe. Calcium aluminate cements (fondu) go off very quickly. In the summer I have to add chilled water to slow down the reaction. If you use it in conjunction with lime the reaction takes place even faster, (unlike with Portland which slows down the reaction). With a Fondu and lime mix you would not have time to place the mix because it will start to go off as soon as you've finished mixing it and by the time you get to the bottom of the batch it will be too hard to place. This is part of the reason I advised a proprietary castable refractory instead.
For the temperatures we fire to I believe any powdered clay should be ok. The cheapest source apart from digging, drying, pulverising and sieving your own free clay is bricklayers clay

Thanks for this... definitely sounds like experimentation is not in order :-)

[stonecutter]

Re: Ciment Fondu / Refractory Castable Question

Pure cane sugar has been used as a retarder in portland based mortar. The study's show that there is an actual increase in strength after 3 days, because the sugar inhibits the set, which allows the portland to have enough time to fully cure.

I've never tried this with any refractory containing alumina, but I see no reason it wouldn't work, or hurt the mix. I have done it to building mortar though, and it did help. Cold water is another old trick, David is on the right track with that suggestion. Warm or hot water has the opposite effect. As to how much sugar to add, From a couple different things I have read, as little as 1/8 % will help, but do not exceed 2 percent sugar added to the portland.

[di11on]

Re: Ciment Fondu / Refractory Castable Question

Thanks for that! I think I'll go with the tried and tested though... since I can at least find all the materials for that!

I have some questions about my build... I've posted them here: http://www.fornobravo.com/forum/f6/i...hts-20644.html

[Tscarborough]

Re: Ciment Fondu / Refractory Castable Question

Just to clarify, that is 2% of the portland, not the total.

[stonecutter]

Re: Ciment Fondu / Refractory Castable Question

Just to clarify, that is 2% of the portland, not the total.

Oops...I thought I mentioned that. I don't recommend taste testing either.

[di11on]

Re: Ciment Fondu / Refractory Castable Question

This link seems to suggest adding gravel/crushed brick to the mix (whether you use portland or ciment fondu). How come this is not present in the home-brew mix?

Most mixes I've seen suggest crushed brick, but I'm finding that hard to find. Would a mix with ciment fondu, gravel and sand (in the correct proportions) perform better than the home brew mix?

Is it better to compromise the cement quality (heat resistance) or the aggregate?

[Tscarborough]

Re: Ciment Fondu / Refractory Castable Question

Homebrew is MORTAR, adding grogg makes it CONCRETE. DO NOT use gravel, buy cheap brick or firebrick and crush it up. Normal aggregate leads to explosive spalling under fire.

http://youtu.be/CNcFwByeUzw