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bernerdog 06-16-2008 08:24 AM

advice on design elements
I`m a long time lurker finally allowed by SWMBO to start build on a 42" and hope to use little or no concrete or block. Here is the plan with numbered questions--steel frame of 2x3x3/8 tubular welded steel and fabricated vent (have a welding shop!). Planned a deck 7' deep and 6' wide and cut the steel before deciding it looks bigger than need be since I hope to go high tech and steel all the way to the finish coat. The deck will have 5 cross pieces about 18" apart covered with not-too-heavy plate upon which 1 or two layers of FB board or equivilent will rest and dome will be constructed, covered with 2 or more layers of FB blanket before stucco coat. Q`s1-4: How much can I shrink the deck(5'x6' or even smaller?)? Do the boards need to be glued/fastened to the steel deck(and if so, how)?Will one 2" layer of board be enough or do I need 2? Knowing the insulation mantra of this site, do folks think I need more than two blanket layers for this igloo oven (remember no concrete/vermiculite). I very much would like to buy from FB if even arguably comparable in price as I am HUGELY indebted to James and this forum. I willl enquire directly when my specs are finalized based on your input.Q5: I`m guessing that re-frax will be uneconomical to ship-if so will dry mix HeatStop work for brick work and cladding?More questions to follow if I can figure out how. many thanks

dmun 06-16-2008 09:44 AM

Re: advice on design elements
1) 42+8+4+thickness of wall=width. You'll want another few inches in front for your entry, landing, and vent.

2) 2" of cal-sil board is fine.

3) 2" of blanket will work, but remember it's not spherical: It has to overlap to get full coverage. That's one of the advantages of a vermiculite concrete overlay: It lets you get a uniform shape for stuccoing your igloo.

4) Buy from FB by all means. Good products, good price, only downside is shipping.

5) Isn't heat-stop made in upstate NY? You might be able to drive over and pick it up.

CajunKnight 06-16-2008 05:43 PM

Re: advice on design elements
Welcome aboard bernerdog

bernerdog 06-16-2008 07:33 PM

Re: advice on design elements
Thanks for input--sure hope to hear from steel people re:above questions. I think I`m overbuilding but I`d hate to have problems after-the-fact. If i don`t shrink the base, it`s 400 lbs. (w/o plate top) to move from shop to home. Do I fasten the FB board to the plate deck or let gravity and weight carry me through construction? HeatStop in 50 lb. dry bags is availalable locally but I haven`t seen raves (or even much comment) compared to FB`s product--what do folks think. Dmun--I just found 30% alumina firebrick 9 1/2 inches so presume that replaces the 8" suggestion in your estimate--it is the blanket and finish layers that have me a little perplexed. Two layers of blanket enough or should I spring for a third? Costs are relevant but good function trumps for me. I built a beautiful AS barrel on triple natural fieldstone arched base about 12 years ago but put the poured hearth right on the massive base w/o any insulating area whose importance just plain escaped me. Another ton or two for the vault and cladding! It obviously never worked but will be there for years unless someone takes a bulldozer to it. Hence, my reluctance to get into concrete/cement/block again. Any and all suggestions deeply appreciated.

dmun 06-16-2008 07:46 PM

Re: advice on design elements
The only negatives I've ever heard about heat-stop is the pre-mixed wet stuff in tubs. It doesn't harden to a waterproof bond, and has a short shelf life.

The Heat-Stop 50 dry bagged mix is great. It's what I used. It mixes easily, remains workable for more than a few minutes, spreads like creamy peanut butter. I recommend it.

If your oven is properly insulated your framework won't even get warm except around the mouth of the oven. And keep looking for 8" firebricks: it's the fireplace standard, and they should be around somewhere.

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