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-   -   Mortar for the Dome? (& insulation?) (http://www.fornobravo.com/forum/f44/mortar-dome-insulation-18177.html)

Spinal 08-04-2012 04:24 PM

Mortar for the Dome? (& insulation?)
 
Starting to think about the internal dome...

I found a supplier for the fire bricks, and for the fb board (and maybe even the blanket) that said, I'm not sure what I should be mortaring the fire bricks with.

Should I be using fire clay, fire mortar, fire cement etc? There are so many options! Can someone provide some clarity?

Also - for the insulating blanket, how many meters have people used for a 42" dome?

Finally - I'm guesstimating about 180 bricks for the dome... does this sound right? And how much fire mortar/cement/clay should I be looking at buying?

M.

Les 08-04-2012 06:27 PM

Re: Mortar for the Dome? (& insulation?)
 
I went through 277 brick for my 42 inch. I did have a lot of scrap. In regard to the mortar, the home brew works well and it's a LOT less expensive than the mortar that you would buy.

Dino69 08-05-2012 05:20 PM

Re: Mortar for the Dome? (& insulation?)
 
I am using the home brew mortar right now. Although I can not compare it with a name brand refractory mortar, I have never used one, it seems to be holding up well. It is very easy to use and was way cheaper than anythig else.

I have used about 180 bricks so far and I am building a 42" making only side bevel cuts to reduce the inverted V. I trashed or experimented, with the home brew, about 5 full bricks so I guess I actually only used about 175 bricks.


David

Spinal 08-06-2012 08:45 AM

Re: Mortar for the Dome? (& insulation?)
 
Thanks :)

Regarding the mortar... I'm umming and arring about what to use! Homebrew sounds like the plan, but I need to find a calcium aluminate supplier in the UK - which isn't proving easy!

m.

david s 08-06-2012 01:33 PM

Re: Mortar for the Dome? (& insulation?)
 
The home brew doesn't use calcium aluminate cement. The difficulty with using calcium aluminate is that is goes off really fast, therefore requiring mixing small batches all the time. It is also expensive stuff. The home brew using 3 parts sand, 1 part Portland cement, 1part fireclay and 1part lime is so much easier, cheaper and does the job perfectly adequately. If using calcium aluminate cement and lime you will find that the lime acts as an accelerant and the stuff goes off even faster. When combining Portland and lime though, the lime acts the opposite and makes the mix go off slower.

Spinal 08-06-2012 01:49 PM

Re: Mortar for the Dome? (& insulation?)
 
I was planning on a 3:2:1 mix (3 parts sand, 2 parts fire clay, 1 part calcium alu - no lime). It should conduct heat better than portland, thus acting as a thermal heatsink rather than an insulator...

david s 08-06-2012 02:29 PM

Re: Mortar for the Dome? (& insulation?)
 
I can't really see why, there would be little difference in the density of two mixes. It would be marginal at best. My feeling is that the lime and Portland brew is better because of its better workability and it's way cheaper.

Spinal 08-07-2012 01:36 AM

Re: Mortar for the Dome? (& insulation?)
 
Quote:

Originally Posted by david s (Post 136187)
I can't really see why, there would be little difference in the density of two mixes. It would be marginal at best. My feeling is that the lime and Portland brew is better because of its better workability and it's way cheaper.

It's not about density... it's about alumina content... HAC as it's known in the UK (High Alumina Cement) can have up to 93% or so alumina, which makes it great for refractory mortar...

The downside (debateably) is that it sets quickly without a retardant...

M

david s 08-07-2012 02:25 AM

Re: Mortar for the Dome? (& insulation?)
 
Quote:

Originally Posted by Spinal (Post 136216)
It's not about density... it's about alumina content... HAC as it's known in the UK (High Alumina Cement) can have up to 93% or so alumina, which makes it great for refractory mortar...

The downside (debateably) is that it sets quickly without a retardant...

M

The cement content is only about 15% so any advantage would be severely diluted by the numbers.

Mistertoy 08-07-2012 06:17 AM

Re: Mortar for the Dome? (& insulation?)
 
Quote:

Originally Posted by Spinal (Post 136185)
I was planning on a 3:2:1 mix (3 parts sand, 2 parts fire clay, 1 part calcium alu - no lime). It should conduct heat better than portland, thus acting as a thermal heatsink rather than an insulator...

If you are set on using calcium aluminate then I would not use 2 parts fireclay. I used calcium aluminate and did a number of trial batches to get the feel of different proportions, how it worked and fast it set. You do need to make small batches and when it is hot is really does go off quickly. I would suggest 3 sand, 1 fireclay and 1 calcium aluminate. I used similar but replaced 1 of the sand with finely crushed firebrick (grog) but this did made the mix harder to work with.

Brett


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