Found a "grill" in my backyard

[pcampbell]

We managed to buy this house a couple of months ago without noticing the remains of a stone/brick grill shoved in the corner absolutely entrenched by overgrown weeds.  My wife discovered it and I took a glimpse of it and I figured it was garbage (which it may be)..

Yesterday a friend and I got a little ambitious and filled 3 landscaping barrels full of weeds and uncovered it a little.  The upper part is a bit rough but the sides and foundation appear to be very solid.  It is lined with S&F fire bricks which suggests it is from around 1960.

I guess what I'm wondering if this can be salvaged and transformed into a pizza making oven.  Pardon the weeds I am waiting for the grass guys to come empty my bins so I can do some more work!

[pcampbell]

My wife and I decided that in the spirit of simplicity and being low impact (both environmentally and on our wallet!),  we are going to build an adobe or cob oven ala American Flatbread.  The bottom will be used for wood storage.  I started demolition today by removing the chimney.  On the bottom to make more room for wood, I removed all of the firebricks.  I now stand corrected the firebricks are "Lehigh", the S&F brand are just red.  I was able to save a good number of firebricks.  I am guessing 24 bricks will be used for a 27" internal diameter dome. 

Next thing I think is to figure out how we will create a level platform for the oven to sit on top of. 

[pcampbell]

I knocked over the chimney and over the winter bought 500# of cement mix.  Our shed leaked and turned my cement mix into bags of concrete!  After that I was having hard time getting motivated but after watching Anthony Mangieri's videos posted on here the other day, I decided to GET TO IT.  Stopped by the local building supply place today mix and poured (all by hand!) a 5" thick steel re-enforced slab.  The inside dimensions are 41" wide x 35" deep.   As the current plans go, this will be a low dome mud oven.

[widespreadpizza]

Patrick,  you are going to put insulation over that slab before you build your oven right?  Just wanted to make sure. -marc

[pcampbell]

I just started reading Kiku Denzer's "How to make your own earth oven" and I was thinking at first, we'll probably just make a temporary single layer oven right on top of the slab which has fire bricks for a floor.  Should I be worried about it cracking due to the heat?  The more advanced ovens include an insulating layer.  However, we will put anything on it for a full month to allow it to cure fully.

[widespreadpizza]

Patrick,  the insulating layer is to isolate the cooking floor from the huge thermal mass you just poured.  If you do not use an insulating layer it could take several hours to heat your oven floor to the point of cooking pizza,  especially beacause you have poured such a thick slab.  My slab was poured as recommended @ 3.5 inches concrete,  then the 3.5 inches of insulation.  There is a product that forno bravo sells for this purpose called super isol(meaning isolate).  This product is actually a pretty common refractory material and probably has a thousand and one uses. This allows your oven floor to achieve high temps in a reasonable amount of time and also to be able to rebound from succesive pizzas.  I did not use suoer isol when I built my oven as I went with the vermiculite/concrete mix that had proven to be very effective and was readily available to me.  There are a couple horror stories over on the forno bravo site about people that have proceeded to skip this isolation step (not intentionally) and have gone to great lenghts to try and make the oven work correctly.  There is a plethora of information over there on the forno bravo site.  I would join in over there if you havent already,  and read,  a lot.  I know you have a book to guide you which I have not read,  which I can only gather is one persons opinions written down.  I think the best way to end up with an oven that does what you want it to do,  is to take a lot of documented real life experiences,  process them,  mix them down and proceed with your next step(s).  In the end you are making an educated guess as to what to do.  The bottom line is that no matter what speed you want to cook pizza at,  be it 5 4 3 2 or 1 minute(s),  the oven has to cook fairly evenly top to bottom.  For me  this meant using a floor that was 2.5 inches thick,ie 1 firebrick,  and for the dome, cutting bricks into thirds,  which came out to just under 3 inches.   I couldn't be more pleased with the outcome.  Right now you are going down the road of having a \7.5 inch thick floor,  and a ? thick dome.  I would put down the book(no offense),  and jump back in to cyberspace,  it's gotten you this far.... there is a lurker of this board that helped me and many others along the road of the self built oven.  He is DMUN,  a walking knowledgebase when it comes to fire and stone.  I have seen him post over here lately and would appreciate his comments.  good luck  -marc

[dmun]

Well, since I've been called out...

I think your oven base is a little small to produce a working pizza oven. Your smallest dimension is 35 inches. If you subtract eight inches for thermal mass and four inches for high-tech insulation blanket, that leaves you with a diameter of less than 24 inches. That doesn't leave much room for fire in the oven cooking. It also looks like the narrow part of the rectangle is the place where you want to put your oven entry.

Successful ovens have been built with all kind of materials, including mud, clay, stone, brick and various forms of castible refractories. I know mud is cheap, but I question it's ability to hold up under the stress of repeated heating/cooling cycles. In the US, firebrick is so cheap it's almost foolish not to use it. Give some thought to this decision. As small as this oven is, a trunkload of firebricks, or the time to search out used ones, would be a worthwhile investment.

Speaking of investments, insulation is a must. Vermiculite can be bought fairly cheaply if you search around, and the high-tech boards and blankets aren't THAT expensive. An inadequately insulated oven will just DEVOUR firewood, and prep time. Nothing pays like insulation.

By the way, I like your re-sourced base. The stone looks great, and you should have enough left over from your chimney demolition to make a nice door arch and maybe some chimney trim. Did that flue tile survive? Nothing wrong with that if it's in one piece.

Good luck with your project. Think about cantelevering out some wings to support some more oven, landing, and insulation space. These things are a lot of work, and it's best to get it right the first time.

[pcampbell]

"FB Board" and "FB Blanket" both sound like great options.  Guess I should have thought about the overall size before pouring that concrete though!!!     Well sounds like I have some surfing to do.  The flue didn't make it, but we did salvage a lot of fire bricks as well as a lot of these nice stones.

[pcampbell]

dmun I noticed on the FB site that you are in NJ - where abouts are you located?  I am in Bergen county.

[dmun]

Union County here, sent you an email.

Here's a picture from a member over at Forno Bravo who strapped forms to his oven to pour a landing. A similar idea could increase the area of your support platform, particularly since there's a lip to support it on the base. It doesn't have to support the mass of the oven, just the space for insulation.

[Frankie G]

 I agree...

Insulating the slab is critical.  Also... think of the interior room for cooking.  in my AS oven, it is 32"x36"  you have to consider room for the wood that is burning.....  a lot of people do not take that into consideration when they build.... 

My thoughts prior to building:

Safety (not going to burn anything... what if kids are around it when it is fired up)
Practical (will my interior be big enough to cook what I want - but not too big that it takes too long or too much wood to fire and get up to temp)
What will I cook primarily (pizza and Italian grilling or bread?  The second requires a thicker cladding than the first... to hold the heat after the fire is raked out.)

just some thoughts.

Frankie G
www.fgpizza.com

[pcampbell]

dmun et all,

Would it be crazy to consider using fire brick splits cut into 3rds or even 4ths and using them so that the floor, sides and ceiling would only be 1.25" thick?  Is the dome stability going to be a huge factor at this point?

I guess what I am thinking is that our oven is going to be very small, and in addition I am hoping that this is something that is going to be used often, several times a week.  Mostly it is going to be my wife and I cooking 1-2 pizzas at most, or at least that is the plan.   I am looking for quick start up times and don't think I need a lot of mass. 

With this I could also add more insulation.  I am not sure how much.  They seem to recommend 3" of FB Blanket and 2" of FB Board.  I imagine there is an equilibrium you need to keep with the amount of insulation on floor and sides/ceiling... and of course I imagine it is easier to add more on top than underneath.  If there is no such thing as TOO much insulation, I could put 2 layers of FB board underneath and go from there?

I saw it mentioned that splits are more expensive but thankfully we live near Progressive Brick where all fire bricks are 1 dollar!

[dmun]

Would it be crazy to consider using fire brick splits cut into 3rds or even 4ths and using them so that the floor, sides and ceiling would only be 1.25" thick?  Is the dome stability going to be a huge factor at this point?

Well perhaps. I think that thermally, it could theoretically work, but there are two structural problems.

First, a semicircle is not the ideal form for an arch or dome. The strongest shape for such a structure is an inverted catenary, the form a chain takes when suspended between two points. For a semi-circular dome, it should be thick enough so that the imagined catenary of gravitational forces is in the center of the dome. I urge you to read this page:

http://www.earth-auroville.com/index.php?nav=menu&pg=vault&id1=2

Second, this is not a decorative filigree. It's a firing chamber that subject to big thermal stresses, and that you are going to be running out to throw logs into when you're in the middle of doing something else. It has to be pretty strong. Also, homemade brick ovens are subject to some cracking. You want your oven to be pretty self-supporting independent of the mortar that holds it together.

I built a pretty thin dome,  with standard firebricks on their edge with every angle cut to fit. I'm not sure I'd go to all that work if I did another one. Like you, I wanted a quick heat-up, and a wood-efficient oven, but anecdotal evidence seems to show that my oven heats up in about the same two hours as everyone else's.

I know your stand is small, but the mass of the oven is the dome and floor. There's no reason why your insulation and cladding can't cantilever out over the edge, as those don't weigh that much