Starting my build

[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

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

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!

[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

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!

[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

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

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

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

Rather than casting your oven in the garage and then trying to move an unwieldy shaped +400 pounds into position on the stand...Borrow a shade canopy and cover the casting work area of your oven stand/foundation/slab. It will make your life a lot easier working in the shade. Remember you will need to do your insulation slab at least a week before setting your hearth bricks and starting to cast on top of it.

Next cover the insulation slab pour with plastic immediately after you fill up the form. With your dry conditions, make sure all cement & castings are dampened and covered with plastic whenever you aren't actively working. Wet down the casting material daily and when you've completed it & make sure to keep it damp/wet for about a week as it cures.

For you the plastic cover and daily watering will be critical to keep the mixed cement products from drying out too fast. Cement needs water to cure, it's actually forming long, microscopic crystals in the slab during the week or more of curing and needs the water to form and set those important internal structures. Remember that the perlcrete/vermicrete will also need to be kept cool/damp for a week or so to allow the binding cement to set properly. (By the way, this insulation material is really weird stuff...you'll think in two days that you screwed up and then in 4-6 days it firms up enough to remove the forms. It will always be crumbly, but it has great compression strength and will easily support the hearth bricks & dome casting--so, no worries.)

[almondsurf]

Re: Starting my build

Thanks so much. I am going to pick up the base insulation today. I hope to be working on that by this weekend. Is the v/p create supposed to be an oatmeal texture? I was wondering how much water to add?

I am quite worried about casting in this dry climate after what happened to the slab. I was planning on watering it at least 2 times per day. I figured I'd just wet it down, then cover with a tarp, then wet, then cover.... for a week or so.

[NCMan]

Re: Starting my build

I think you'd be better off just covering it w/a sheet of plastic and then some cardboard or plywood. I'd leave it that way for a few days or even a week or so. Just like concrete, keeping the mix water in the slab, not watering it down, does a lot more to strengthen a slab then soaking it down does. After you do uncover it, allow it to dry a bit before moving on to installing your hearth bricks. Just my 2?.

[SableSprings]

Re: Starting my build

Here's a link to a perlcrete mixing video. The thread is on the Forno Bravo site somewhere, but I thought since I had this it would help you for the upcoming work.

https://www.youtube.com/watch?v=1Ot8vucmVis

Yes, the final mix when correctly mixed seems a bit dry...you should be able to take a handful, squeeze and it will hold together. The wheelbarrow & hoe combo is great for mixing. Make sure that you mix the Portland cement into the perlite first. When you add the water it will actually wash the cement off the perlite...that's normal. A little mixing and it comes back together. The biggest issue is making sure that you mix water in very slowly and completely before adding more. I used a watering can to make the water additions a little more gentle. My water source was the 5 gallon bucket, so I could keep track of how much I'd added.

In the video, he gives you some estimates of water used. Note that having some extra perlite and cement on hand is good...you're going to be using some again later, so don't get caught short on supplies.

NCMan is correct, don't soak things down, just keep it moist while the curing process is underway. As he suggests, the plastic covering (with maybe a piece of plywood on top to keep it in place) will probably be all you need to keep it moist if it's under shade.

Be aware there is another method that combines the cement and the water first, and then the slurry is added to the perlite and mixed. I have no clue on water proportions so I'll suggest you continue with this method until you get a hankering to experiment...

[david s]

Re: Starting my build

I've found the correct ratio of water is 1/3 of the volume of vermiculite or perlite. If you add too much it pools in the bottom of the barrow and tends to wash the cement off the grains of perlite. Also if you use 50% vermiculite and 50% perlite it makes a more workable mix than either of them alone. Also adding a small amount of powdered clay to the mix helps make it more workable. I use a handful for every 10 litres. Because around double the amount of water is used than is required for the hydration process, there is no need to keep wetting the stuff down. Just cover it for 24 hrs then allow it to dry in the sun and wind, if you have any. It will take about three weeks to dry out in ideal drying conditions.

Trying to dry it with fires alone after building straight over it is a bitch. It will takes many weeks and fires to eliminate all the water. Some holes through the concrete supporting slab between the vermicrete and the storage area under work well to help this moisture escape, particularly if it gets wet again after heavy rain.

The doc on this post may help you.
http://www.fornobravo.com/forum/f2/v...tml#post158957

[cook4fun]

Re: Starting my build

Mike - I really appreciate your insights regarding the construct of an oven, especially the perlite / concrete ratios and the height of the oven floor. Regarding "belly button" height, I have designed (but not built - that happens in two months) the oven floor to be at mid-chest height (about 10" higher than belly button height). I've read in lots of forum's that "I wished I had made it higher", so I'm thinking the route of going a bit higher - especially given the angle that we have to bend at the waist. My plan is to use the FB Cucina stand (40") placed on top of a 6" slab (totalling 46"), 4" of perlite / portland mix @5:1, (50"), 2" of FB CalSil board on top of that (52"), and then the oven hearth 54"). I'm 5' 10 (and a bit), but 57 and can no longer bend like gumby the way I used to...your thoughts are greatly appreciated.

-