#1  
Old 09-07-2010, 03:21 PM
Apprentice
 
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Location: Napa, CA
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Default What Concrete for a cast flue?

I am getting to the point soon (hopefully) of starting my flue for my 42" Pompeii and have decided that I would like to cast my own using wood forms.
  1. What type of concrete should I/ can I use?
  2. Can fibers be used for reinforcement?
  3. Are there min and max lengths of the chimney?
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  #2  
Old 09-07-2010, 04:41 PM
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Default Re: What Concrete for a cast flue?

I found the following mix on the web,

Ingredients:

River gravel or crushed fire bricks
Sand
Calcium Aluminate cement. (if available in different grades choose the better one)
Lime (lime is usually cheaper, about 80% of the cement price)
Water
You can add into this mix a little standard Fireclay if you like.

Mixture: (parts ratio is 3 x 2 x 2 x 0.5, plus water)
3 shovels of the gravel or crushed firebricks
2 shovels of sand
2 shovels of the cement
half shovel of lime

-----------------------------------------------------------------
  1. Has anyone used this mix?
  2. Where do I get "Calcium Aluminate Cement" (around Napa, CA)?
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Old 09-07-2010, 05:18 PM
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Default Re: What Concrete for a cast flue?

I would not recommend any gravel, although crushed firebrick is fine. Depending upon where you are located, the gravel could have a very different rate of thermal expansion than the rest of the ingredients and cause major spalling at high temps.
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Old 09-07-2010, 07:39 PM
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Default Re: What Concrete for a cast flue?

Have you used this mix design?
Or used another?
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Old 09-07-2010, 08:33 PM
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Default Re: What Concrete for a cast flue?

There are pre-mixed castable refractories out there. I would not feel comfortable casting my own custom flue with a site-mix, but I did use one to fill in the gaps around my terracotta flue and firebrick.
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Old 09-08-2010, 12:40 AM
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Default Re: What Concrete for a cast flue?

Yes you would be better to buy a premixed castable refractory ie just add water. The flue doesn't get that hot (as evidenced by the inside being black ie under 300 C) so shouldn't be too much of a problem, although if it is relatively thin and the outside is exposed to the ambient temp then expect the flue to crack, due to temp difference. You really need to insulate it a little and have an outer skin to prevent this.
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Old 09-08-2010, 07:38 AM
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Default Re: What Concrete for a cast flue?

Quote:
Calcium Aluminate cement. (if available in different grades choose the better one)
Lime (lime is usually cheaper, about 80% of the cement price)
We are warned off mixing calcium aluminate cement and lime: They are apparently incompatible.

With flue tile so cheap, why would you mess with this difficult material?
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Old 09-08-2010, 02:28 PM
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Default Re: What Concrete for a cast flue?

Quote:
Originally Posted by dmun View Post
With flue tile so cheap, why would you mess with this difficult material?
I want to cast my own because I want an offset and dont want to have to pie cut a bunch of 13x13 liners.

Making the forms is the easy part.


Eric.
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Old 09-08-2010, 03:30 PM
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Default Re: What Concrete for a cast flue?

Flue as in the whole vent area?
I cast my vent using premix, just added water. I added some crushed firebricks to add a bit more volume to the mix. 25 lbs of this Rutland refractory cement premix was just enough to fill the form.
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Old 09-08-2010, 04:42 PM
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Default Re: What Concrete for a cast flue?

Is this the material?

If so, does anyone know where to get it (or a suitable replacement) in Northern California, I live in Napa, CA and work in Pleasant Hill, CA. (a bedroom community about 30 minutes from San Francisco)

I did check their website and called a few places (mostly Ace Hardwares stores) and was told that they did not carry that material.
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