Saint Helena Oven
After hours spent reviewing various ovens and postings, I think I'm building what seems to be a fairly typical oven. I've documented my progress to date with the camera, but have been too lazy to post.
I now have a few questions and would like to document my overall progress, so I believe it appropriate to start a new thread for my oven. Progress pics to follow..
Spent a full day excavating foundation, with a hired helper. Had to transplant a small redwood tree, deal with lots of roots, sprinkler pipe and electric, etc.
Had to shovel all the dirt 3 times. Once into wheelbarrow, once from barrow to trailer, once from trailer to fill site.
It was hot and not the funnest part so far.
The foundation forms then sat like this for about 3 months, so long that they warped and I had to replace them when it came time to actually pour concrete.
To pour the foundation, I rented a mixer/trailer that came with my concrete in it. Was kind of fun renting and operating it. Made a lot of noise spinning around behind me while I towed it home. Cost $200 but I didn't have to mix any concrete, just pour into barrow and wheel into place. Took less than 20 minutes to get all the concrete (.8 yards) into the forms. Took a lot longer than that to finish it of course. Ordered brown concrete. It doesn't match the patio but it's better than gray I think.
I placed tie down bolts in the corners. And I didn't leave those wood blocks in place, replaced them with concrete ones. I also added some more rebar to fill the gaps you see.
Slab is 5.5 inches thick with gravel underneath.
I used the method of dry stacking blocks, spanning the opening with angle iron. Grinding the space for the angle iron probably was the hardest part, although it wasn't hard.
I filled every other core with concrete and rebar. Used my new Home Depot mixer and troweled right from mixer into block using a cardboard form. Simple.
I wish I had bought the block with slots across the top for the top row, I would have liked to run rebar horizontally along the top. Instead I drilled holes in the sides of the blocks across the opening span and ran bits of rebar between blocks. I then formed under those with a piece of wood and filled them with concrete. Made them a lot more stable.
I cut the rebar off with the grinder at the top of the concrete other than in the corners. I left the corners a few inches high to bury in the slab at the next level.
This part I'm not that comfortable with in retrospect. I poured a 7.5 inch slab, the first 4 four inches being structural concrete with rebar, the rest being a mix of concrete and vermiculite/perlite.
Built a stand for the mixer and poured straight into the forms. Other than lifting 90 lb bags of concrete into the mixer, not hard.
The part I'm not comfortable with is the span and the weight I'm asking a slab of concrete only 4" thick to carry. I've decided to place a support in the center of the wood storage area. I've got little boys that will undoubtedly use that space as a fort, I'm freaked out by visions of a collapse. I plan to make the support out of large metal pipe like used for fire sprinklers in commercial applications. I'll get each end threaded and use bolt down couplings at the ends. I can twist the couplings so that there is tension on the support and then bolt into place. Open to other ideas.
Vermiculite layer on table
The mix of 5 parts vermiculite and 1 part portland didn't seem to work for me. I went more like 5 parts vermiculite 2.5 parts portland.
Smoothing the vermiculite/concrete mix was tough, the more you floated it the more the vermiculite rose to the top. I settled for a roughly level but not very smooth surface.
I decided to lay the oven floor bricks perpendicularly for simplicity. I laid them in 1:1 fireclay/sand mix. The fireclay/sand mix doesn't adhere to the vermiculite concrete incredibly well, even when fully dry. You can pop bricks out with relative ease. I assume this isn't a big problem.
My building supply place only had firebrick that is 9"x4.5"x4". This is larger than is suggested and will make building the dome without gaps harder. Not sure if there are other ramifications. When you see my dome you will see that this led to an overlap with the 2nd chain.
Another thing I'm not that delighted with in retrospect. I should have laid the first chain bricks sideways. The size of these bricks has led to a big overlap when chain 2 was introduced. I'm also not sure I should have laid the bricks at the opening the way I did, but they seem fairly solid now.
Here are the second and third chains. You can see the overlap caused by the way I laid the first chain and the 4.5 inch width/depth of my half bricks. It seems strong enough, but curious as to any input. I could still lay another round of bricks around the outside of the first chain, although this would add significant thermal mass to the oven. I'd have to add more floor bricks, etc.
Notice I've placed forms inside, but I'm not really using them just yet other than as guides. Using wedges to place the first rows. I plan for the forms to come in handy when I get closer to the top. I plan to use pieces of flashing or cardboard to span the gaps between the form wings. Or I could probably fit in some more form wings if I did it now.
I'm now at the point where I need to figure out the doorway. I plan to span with an arch using the wood form in the pictures, butting the dome against the arch and on top.
Welcome aboard JC,
St. Helena to Healdsburg isn't far -- though you grow Cabernet Sauvignon, where we grow Pinot Noir. Everything looks very under control, and looking good. I'm sure you will get lots of input from other builders, but I can kick things off.
I don't think you need to worry about how smooth the insulating layer is/was. You cover it with the sand/fireclay layer so that your cooking floor will be smooth enough. As long as a pizza peel doesn't catch, all is well. The 5:1 vermiculite to Portland mix seems a little funny when you mix it, but it definitely does set, and its only goal in life is to be an insulator. Also, the sand/fireclay mixture doesn't adhere -- it's a layer than your cooking floor rests in, that helps it stay level.
Don't worry about the re-inforced concrete spanning the openning. This has been done may times before. On your side, think about the fact that you have a course of concrete block on all four sides supporting the oven (including the angle iron and block course over the open span). Also, remember that the oven rests its weight on the outer edges of the hearth, pretty much on top of the block stand. You are in good company -- there are zillions (that's a technical term) of this style oven throughout Europe. A vast majority of which are on more simple concrete platforms than you are building.
What do other builders think about the first course being more narrow than the following courses? Would you build up the first course with another layer? It would not add enough mass to make a difference for cooking, so I think the question is whether it would add stability.
On the internal forms, gravity doesn't really take over until the last few chains. Brunelleschi built the duomo in Florencee without any internal supports -- and the Artigiano builder says he does not need any forms. Hmmmm.
Keep the photos coming. Everything looks great.
Arched Entry Part 1
Well. The Arch over the door is harder than I thought it would be. Particularly making it meet the oven walls. It's not complicated, just a lot of angles. I'm not very patient, and I don't have a good strategy for transfer of the angles to the bricks.
I'm running a half marathon tomorrow and wanted to get the arch done today so that it dries and can bear the weight of the next chain. So even less patience.
I butted the sides of the first few bricks in the door arch against the sides of the 4th chain of bricks.
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