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builder brad 04-18-2009 12:58 PM

best material for flue

I have successfully used the dust from when I cut mt firebricks with sharp sand and cement to build the flue area and part of the chimney in my oven, However I am now finishing off the oven and will be extending the landing area and re-designing the flue area. Unfortunately I have used up all of my brick dust so I tried to source fireclay without success and finally got a 25kg bag of Corderite which I was told is graded firebrick dust.

I have tried to use this Corderite with Sharp sand and Cement in the following ratios 2.2.1 and have got a very rough grainy material without any real strength. I know I could increase the cement, but I used the same ratio with the brick bust and got a really good finish with enough strength to hold up my chimney.

I think the Corderite is going to work out OK, Its meant to have excellent thermal shock properties, I would just like to get some more ideas of mixes ect to use.

Cheers in Advance


david s 04-19-2009 04:32 AM

Re: best material for flue
Try the 3:1:1:1 sand, lime, cement,fireclay. Or use a proprietary castable refractory.

dmun 04-19-2009 06:55 AM

Re: best material for flue
I don't think anyone answered you because we don't know what corderite is.

I found a material data sheet:

Maryland Ceramics & Steatite Company, Inc - Steatite and corderite materials

but it doesn't tell me much.

builder brad 04-19-2009 12:25 PM

Re: best material for flue
cheers David + Dmun,

here is some more info:
Cordierite Grogs

Created by crushing virgin kiln shelves; they are an alternative to firebrick grogs for colour yet do not have the lime-popping, problem often associated with firebrick.

I guess that I would probably do well to add some fireclay to the mix as suggested.

I have needed to cut away part of the flue that I made last year with the firebick dust, and found that the material was harder than any of the firebricks that I have been cutting, more like cutting a solid piece of porcelin!

I could also recover some of my firebrick off-cuts and bash those into dust, just want to use the best material for the job, as I wont be changing anything else once I finish this time!


dmun 04-19-2009 03:00 PM

Re: best material for flue

bash those into dust
If you have pottery connections, get someone to do that for you in a ball mill, save your arms and lungs.

david s 04-20-2009 05:11 AM

Re: best material for flue
I've crushed several firebricks into grog as an ingredient for a castable refractory. Old fashioned pounding with a hammer. It's a hell of an effort for a small amount of material, but if you have the time and your material is free or surplus, go for it.

builder brad 04-20-2009 12:59 PM

Re: best material for flue
cheers David & Dmun,

I have a really big hammer, dust mask and goggles, so I guess that is what i will do.

I may only smash up a couple of bricks worth,and use this in the first inch or so of my flue arch, and then i will switch to the Corderite in place of the firebrick dust. this stuff is suposed to have good refractory properties and is supposedly better than firebrick grog when used in pottery production. The mix that used the Corderite a couple of days has now set and its very hard now, just a little coarser than the mix with the firebrick dust.


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