Starting my build

[almondsurf]

Re: Starting my build

Thanks for the info on the build and great idea to put in panel board. I assumed heat would excape out the bottom of the oven if I left a gap (expecially with all this attention to detail with heat retention and such), but then again, heat rises.

Funny you should mention Reubenandrena's thread. I was just reading through that this morning. Looks like he hasn't posted in a while though. Not sure if he can give any feedback. I was wondering how many cubic feet of cast material he used? I also noticed his final cast was just 2.5" thick:

"I used 7 55lb bags with a final wall thickness of 2.5."

Maybe I'll do like he did and cast mine in the garage so I won't dry so fast.

[SableSprings]

Re: Starting my build

Also SableSprings, It looks like in your build (which looks great btw) you placed the fire brick dome on top of the firebrick floor. Do you think it would be better if I cut the firebrick floor to the dimension of my internal surface area, then cast the dome around that brick floor so that my cast rests on the vcreat insulation?

At the time I built DD (Doesn't everybody name their oven?), you are correct, I just left the perimeter hearth bricks intact/untrimmed and built the dome on top (I was lazy and didn't think/know about possible consequences & limitations of that method). If I build another oven, I will cut the hearth bricks so they align parallel with the dome's inner surface and are inside that dome perimeter by 1/4"-1/2" (5-10 mm). As materials in the oven heat & cool they will expand & contract...obviously different materials & thicknesses will not "move" the same way or amount. The gap around the hearth perimeter allows a little play in the system and more importantly, if you need to replace (or level) a hearth brick you'll have a much easier time of it.

The perimeter gap soon fills with ashes and you'll never notice it after the curing process. I would use bender board or cheap panel board around the perimeter of the cut hearth bricks for the inside, lower cast form. Yes, the outer dome casting would be made on top of the insulation slab (same level on which the hearth bricks are laid). When you're done, you won't even have to remove the bender/panel board as the initial fires will simply burn it away leaving you the perfect little gap

Since you will have plenty of insulation with the 2" of ceramic fiber batting over the dome, cutting back a bit on the perlcrete/vermicrete top layer thickness won't hurt you at all--1" is plenty of material for creating a base "stucco attachment layer".

Sounds like the plan is well on the way...pizza for the 4th of July!

p.s. It looks like the thread on Creating a Form for a Cast Oven by Reubenandrena is going to be a gold mine for you.

[almondsurf]

Re: Starting my build

Yes, I have looked through LOTS of other posts and each has their own method. David S has posted quite a bit on some of the casting threads. I recall him mentioning that a thicker cast isn't necesarily going to be better when it comes to casting. I plan to cook mostly pizza and breads. I'm sure I will through in some other dishes from time to time. I'm fine with doing 3" if it will be a better oven, I will just have to make a thinner vcreat layer on the outside or something.

Also SableSprings, It looks like in your build (which looks great btw) you placed the fire brick dome ontop of the firebrick floor. Do you think it would be better if I cut the firebrick floor to the dimension of my internal surface area, then cast the dome around that brick floor so that my cast rests on the vcreat insulation?

[SableSprings]

Re: Starting my build

Although I haven't cast an oven, the 2" seems to be on the thin side. With 1/2 firebricks on the dome, the typical brick oven dome's heat sink is more along the line of 4.5" thick. Do you intend of doing some longer term cooking...batches of bread, roasts, turkeys, etc...other than just pizza? More mass will give you more consistent temps for longer periods of time. I would think you'd want to be casting something more along the 3-4" thickness range for the dome. What little work I've done with casting materials tells me that a thinner layer may also set you up for some significant cracking problems (even with the ss needles) during the initial drying process. It will take slightly more wood to fully saturate the oven, but it will give you a lot more flexibility and potential for your oven if it's thicker than 2".

Hopefully some of the folks who have cast an oven will weigh in on the thickness of the dome...I assume you've searched the threads in alternate oven types for thickness of walls. Glad my input's been useful.

[almondsurf]

Re: Starting my build

Thank you Greenman. Sounds like I should be good with my revised measurements of:

32" enterior oven
2" thick cast (is this too thin?)
2" thick ceramic blanket
2" thick vermicreate layer (mostly to smooth out the blanket and prep for stucco)
1" shell of stucco and waterproofing

That puts me at roughly 46 inches total.

Dave, or any others who have casted before, do you think that a 2" cast is thick enough? The refractory salesman seemed to think so but I'm not sure he has done anything like this. Thanks for the help!

[Greenman]

Re: Starting my build

Hello Almondsurf - the outer 'shell' of your igloo will be fine at less than 1". Mine is mostly less than an inch. It varies a bit as you fill any low spots or gaps in the insulating layer. It is only a waterproof sealing layer and is deceptively strong, could be the shape I suppose. Physics is not my forte.

Sounds like your 'treasure hunt' is going well. You are well on your way to a thrifty oven.

[almondsurf]

Re: Starting my build

Sorry to be so wordy...hope this diatribe helped

Are you kidding! I get excited all day to check this post and glean wisdom from you experienced folk. You have given me some valuable information, specifically about the refractory cast resting on the concrete slab. That is a great point I would have never known. Thank you! I am now going to plan to do a 6" vermiculite or perlite mix for the base insulation. I did the base low on purpose of adding AT LEAST 4" of insulation under the bricks. 8" actually puts it right around the belly button (I just ran out to measure).
Also, I will plan to make the base insulation wide enough so that it extends past the refractory cast by at least an inch (insulation all the way around as you mentioned).

Crazy thing... I was at a clients house this afternoon and noticed a huge sack/bag of, can you guess?... Perlite!!! I asked where he got it and he said, "oh, just picked that up down at the nursery. Only like $10 for the whole bag." So, I'm pretty excited I can just go pick some up tomorrow.
As for the drying time. I actually think that is fine as I can't pick up the insulating blanket (and castable cement if I go that rout) for 3 weeks or so. That will give me some time to let the perlite dry. I assume it will dry fast here (did you see my concrete slab?).

I plan to use the ceramic batting for the dome insulation. That stuff seems pretty inexpensive for the work it will save me let alone the better insulation (I hope).

They will sell me the 2"x2'x12' 8lb for $3.14 linear ft. or $37.50 per roll.

Using the formula to find my surface square footage to be covered by the blanket: 4(pi)(r^2)...
r= the radius (or half the width of the outside of my 3" cast).
So... 4(pi)((3.1666'/2)^2) = 4(pi)((1.58333)^2) = 31.5 sq ft.
Then we divide 31.5 sq ft in half (oven is half sphere) = 15.75 total sq ft. (not including the flue gallery).
So, two rolls should be plenty of batting / blanket to cover the oven and flue gallery. I think $75 is relatively inexpensive IMHO.

Thank you again SableSprings for your very helpful and detailed post!

[SableSprings]

Re: Starting my build

I totally understand the $$ issue on the hearth insulation board. The perlcrete/vermicrete option is going to be a lot less expensive and will work just fine. I did look at your design drawings and it appeared that your outer refractory cast is going to be resting on the concrete slab. Make sure you DON'T do that...the concrete foundation will suck the heat out of your casting. You want to make the base insulation pad large enough to cast the dome shell on top of the perimeter of the perlcrete base. I only formed up and poured about a 3" thick slab of perlcrete between the foundation and the footprint for my oven--I wish I would have doubled that. So, my brick dome rests on the same perlcrete slab as my hearth bricks and my outer 5"-6" of perlcrete insulation for the dome connected and joined the lower base insulation pad--effectively enclosing the entire oven with insulated material.

At the relative low cost of the perlite & cement--going 6" thick for the hearth insulation base would be my current recommendation. The downside is it will make your oven floor a bit higher and you really want to make sure it's the correct height for you (and other bakers in the house). You don't want to bend over much to look inside while doing pizzas but you want to be able to easily work the peel. I find that if your hands are about at belly button height when you hold the peel, you will have a much easier time working the oven. So I look at the baker's working hand height to determine the height of the cooking floor.

Be aware that you will have a significantly longer time needed to dry out a perlcrete/vermicrete base pad than with the board product (especially going with a 6" thick perlcrete base slab). Some folks even recommend drilling drain/vapor exit holes through the foundation slab below to speed up the drying process of the insulation base layer. The thought being that once you put on the hearth bricks, venting steam and moisture from the wet perlcrete below will be much more difficult.

Hands down, the ceramic batting for the upper dome is the best and I'd still recommend it over perlcrete or vermicrete. I don't have any experience with dome casting materials...see if you can get the ingredient proportions for the Surecast commercial product to compare. It sure sounds like a nice alternative to buying and mixing your own. (Sorry to be so wordy...hope this diatribe helped )

[almondsurf]

Re: Starting my build

So, I found most everything I need at a supply place in Salt Lake City UT. We're going there in a few weeks so this may be a good option.

Vender: Mountain View Power
Ceramic Fiber Board, 2"x2'x3'
Super Wool Blanket, 2"x2'x12'
1" needles @ $4.70 lb

I would love to buy these through Forno Bravo, but the shipping costs are quite high as these materials are heavy. The blankets are pretty inexpensive at the mentioned location if I pick them up, so I am going to be purchasing two 2" layers of the blanket.

The Ceramic Fiber Board is going to run around $170. That stuff aint cheap. At that price, is it still advisable to use over the vermiculite/perlite?

Also, this place has a "just add water" castable cement rated at over 3000 degrees for $37 per 55lb bag. Would anyone advise using this method (surecast brand) over the 1,6,2,1 (clay, sand, lime, cement) method? I will use needles regardless.

[SableSprings]

Re: Starting my build

The Forno Bravo prices are a bit better for the board - 36" x 24" x 2" = $70 ($11.67/sq ft -- it's #IFBBO2436) and 50' of 1" blanket is $75 #IFBBL50 (a bit more than the Pacific material you found). You can get a quote from Forno Bravo and it sounds like it will be worth the effort. Also check around places that install commercial boilers and the like...industrial supply places like that might be able to give you some other sources to check. I have also found "stuff" at places that do demolition work and salvage operations. There are several WFO builds in Utah, search for threads with Utah & insulation sources on the forum...they might name some other suppliers in your area.

Good luck & remember - the material hunt is half the fun!

[almondsurf]

Re: Starting my build

Thank you for the info SableSprings. The info you guys are providing is very helpful. I am currently looking and pricing the FB and blanket. It is hard to come by though. I am trying to find it out of Las Vegas (which is the nearest large city, about 1.5 hrs away). I found the Super Wool Blanket @ Pacific Insulation ~ $60 for 2"x2'x25'. They are supposed to call back on a price for the FB. I guess they even have a hard time getting the Fiber Board in. They had Super Wool Board, but it is $26 per sq ft. for a 2" board, that's $312 for 3x4... Yikes!

[SableSprings]

Re: Starting my build

Or, should I just use Super Wool Blanket for the exterior insulation? I read that I only need 2" of that stuff. I was trying to save cost, but I am having a pretty hard time finding vermiculite (other than here which is expensive)so the blanket might be a good option?

I used perlite instead of vermiculite and found it more readily available in both Landscape/Garden shops and Brick/Concrete supply businesses. My records show I purchased a 4 cubic Ft bag (25#) for a little over $12.50 in 2009. I do remember that you needed to specify the non-silicon treated variety, but the cost compared to perlite or vermiculite at Home Depot & Lowes was far less. I also noticed that the perlite purchased at the Garden shop was slightly larger "grained" than the other bags. Proportions as noted by David for vermiculite work for perlite as well (and these are volume proportions...I just used the bucket method to measure )

In terms of effectiveness and ease of application/use, I highly recommend biting the bullet and using the ceramic board for the base insulation and the ceramic wool blanket type insulation for the dome. I've done both insulation types and would now always choose the commercial ceramic types over the vermiculite/perlite options based on my installation experiences. Although both insulation methods will work well, you definitely will save money with vermiculite/perlite. But when you add in your hands-on efforts (making/removing forms, mixing with cement, curing time, drying time-removing water retained in the perlcrete/vermicrete, etc.) it's not that much of a difference (IMHO).

[almondsurf]

Re: Starting my build

Thanks David. I did search vermiculite and went through around 15 threads and found some info, but not specific ratio's like you have stated. Thank you, that is going to be a huge help.

Good point on the flue gallery, I will modify that to be 3 inches with the rest of the oven (unless, based on the paragraph below, I should reduce it further to 2 inches).

As for the outer shell, I left 1 inch... and now that I think about it, that is only .5 inches on each side. How thick is the typical outer shell/stucco? Would you recommend taking an inch off the refractory cast layer (I have read that the cast can actually be pretty thin, but insulation needs to be pretty thick) or should I shrink the whole design a little. Admittedly, when building the base, I was planning on constructing a 30" oven but thought I could fit a 32 after the base was done, so ether size is fine for me.

Or, should I just use Super Wool Blanket for the exterior insulation? I read that I only need 2" of that stuff. I was trying to save cost, but I am having a pretty hard time finding vermiculite (other than here which is expensive)so the blanket might be a good option?

[david s]

Re: Starting my build

I have taken off the form for the oven base. I figured I would ask the community your thoughts on my design and if I need to modify / change anything. How do my measurements look? I have read quite a few forms on casting the oven, but hope some of you may be able to help me further.

I have attached several pictures of my plan. Please see the pics as a reference. I used tinkercad.com for the mock up. The measurements are in inches.

I plan on using a mixture of vermiculite for my base and exterior insulation. Does anyone have a formula, amounts, and ingredients for a homebrew insulation? I read it is good to use bottles in the hearth insulation; any thoughts on that?

My planned recipe for the cast:
1 part cement
6 parts sharp sand
2 parts hydrated lime
1 part fire clay
4% 1" Stainless Steel Needles (Link)
1% polypropylene fibers

Your plan looks ok, but you've left yourself hardly any room for the outer shell.
I don't think you need to go so thick for the flue gallery.
Only use bottles for insulation if you can't afford the vermiculite.
Use 5:1 vermiculite,cement ratio for the underfloor insulation.
Use 10:1 for over the dome.
Search vermicrete on this forum for more info.

[almondsurf]

Re: Starting my build

Just pictures, no measurements. (sorry, I don't know why the photos are uploading so small??)