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  #11  
Old 09-29-2009, 10:15 AM
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Default Re: Why not insulating firebricks for hearth insulation?

Personally, I would stick with one type of insulation just for the sake of simplicity.
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  #12  
Old 10-01-2009, 04:05 PM
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Default Re: Why not insulating firebricks for hearth insulation?

kebwi,

My original plan was to go a little (overbuild, as usually) heavy on the vermicrete but the local ANH guy made me great deal on a case of 2" Insboard 19. I ended up topping 3" of vermicrete with the board which was really easy and fun to do. I'm pleased with the way it turned out and the fact that I have a primary insulating layer and a backup layer, not to mention that the whole thing cost around $135 to install.

Depending on the insulating firebrick coverage you have, you could always place the bricks under the dome and vermicrete under the landing and entry, OR, work your way from the outer circumference of your dome inwards with the bricks and fill any remaining space with vermicrete. Either way, I'd guess the insulating value of either material is pretty close. After my vermicrete cured I POUNDED on the insulating board to see if I could get it to budge and hurt my hand.
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Last edited by GianniFocaccia; 10-01-2009 at 04:07 PM.
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  #13  
Old 10-01-2009, 04:16 PM
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Default Re: Why not insulating firebricks for hearth insulation?

Thanks. I already passed up the insulating firebricks, and at the same time got my hands on a rather large quantity of leftover vermiculite (that I hope doesn't have too much rockwool mixed into it).

I have been thinking about Insblock 19 too. I haven't decided if I want to just do 4" of vermicrete or if I want to do 2"-3" of vermicrete with 1" of Insblock 19. The latter option is more expensive but I kind of like the idea of having a better insulator directly under the bricks, and also thought that board might be a little more even than direct vermicrete...of course the boards might wobble on the vermicrete for the same reason.

I can't decide. Not sure the board is worth the cost. I can get the 36"x12"x1" for $10.65 locally or a pack of 16 for $92 (or a pack of 8 2" for the same price), from Northwest Iron Works :: Home Page, but which more than I need. I think five or six boards would about do it.

What do you think? Is the Insblock layer worth an extra $70 to $100?
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Old 10-01-2009, 04:29 PM
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Default Re: Why not insulating firebricks for hearth insulation?

I have insblock on top of vermicrete. My board never moved at all. If you get the top of your vermicrete nice and smooth, (well, maybe flat is a better word) the board goes on well and the bricks on top of that even better.
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Old 10-01-2009, 04:31 PM
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Default Re: Why not insulating firebricks for hearth insulation?

Does anyone know if you are supposed to water the insulating concrete during the curing process. I just finished pouring a 5 1/2 inch perlite hearth for my 54" wfo.
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  #16  
Old 10-01-2009, 04:45 PM
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Default Re: Why not insulating firebricks for hearth insulation?

I'd spring for the board for two reasons: $100 for your entire oven to be insulated with 2" IB is really cost-effective, and the board does make a nice platform to lay your oven floor on. Besides, there are a great many ovens out there that have been built on 2" of IB.

I used seven 1x3' boards for my 42" oven which came out to a 53 1/2" diagonal.
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Old 10-01-2009, 07:15 PM
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Default Re: Why not insulating firebricks for hearth insulation?

I used two and a half inch of insblock19 directly on top of my support slab: I laid the blocks down on the slab when it was wet. The surface was flat enough to put my brick floor right down on them without any leveling medium. My support slab never warms up even with a big pizza bake, and is only slightly warm the next day. I recommend it.
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Old 10-01-2009, 11:32 PM
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Default Re: Why not insulating firebricks for hearth insulation?

All right, I'm sold. InsBlock 19 it is! Still unsure whether to go local or mail. I was originally thinking of getting the large box-sets from Northwest Iron Works and using the extra pieces to make the door, but some discussions on FB have put me off that idea now, the thinking being that InsBlock shouldn't be anywhere near the interior of an oven with food in it, so now I'm not sure what I would do with the extra pieces.

Seattle Pottery Supply:
36"x12"x1"-1: $10.65 + 9.5% sales tax = $11.66 = $46.64/ft^3

Northwest Iron Works:
36"x12"x1"-16: $92 + $43.78 shipping = $135.78 = $33.94/ft^3
36"x12"x1.5"-10: $90.50 + $43.78 shipping = $134.28 = $35.81/ft^3
36"x12"x2"-8: $92 + $43.78 shipping = $135.78 = $33.94/ft^3
36"x12"x3"-5: $94 + $43.78 shipping = $137.78 = $36.74/ft^3

Five 12"x36" pieces only works if I leave some of the entry way uncovered by board. Less an issue about insulation, there is the issue of augmenting the remaining uncovered area of the entryway with some other material (small patch of vermicrete?) such that I get a perfectly level surface on which to lay the bricks...so the 3" option listed above is probably less ideal for that reason.

Well, I'll think about it. Maybe eight pieces of 2" makes the most sense. I can use six pieces for the floor and have two more pieces for whatever comes along, maybe some sort of sealed door, or maybe just dump it on Craigslist.

Thanks for the advice.

BTW, for any other folks in Seattle, Seattle Pottery Supply's e-catalog is out of date. It lists items they don't carry and their prices are higher than quoted in the catalog for the remaining items.
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  #19  
Old 12-12-2009, 01:53 AM
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Default Re: Why not insulating firebricks for hearth insulation?

There is a supplier in New Zealand that sells the porous type insulating fire bricks made from pyrolite for under half the cost of traditional alumina firebricks. The supplier says they can take the heat. He even has thin bricks that look like pavers. They are the type of bricks that they put in woodburner type home fireplaces. Can I use these bricks for the Hearth or even the dome. What would be the dissadvantages?

Here is the link:
BRICKS (Fire) #Other Sizes Also Available# for sale - TradeMe.co.nz - New Zealand
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Old 12-12-2009, 08:00 AM
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Default Re: Why not insulating firebricks for hearth insulation?

Of course insulating firebricks will "take the heat". They are used in pottery kilns, and are made to be heat resistant. The question is, what will they do with it...

The brick in a wood fired oven absorbs the heat and reflects it back to the cooking surface. It's what cooks the food. The insulation around the brick helps hold the heat in the brick, and concentrate it. An insulating brick oven would get very hot above the fire, and nowhere else.
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