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tektonjp 09-14-2011 04:56 AM

Economy 24" cast in place in Japan
I've been doing pizza in the oven the past couple of years, slowly progressing in technique to an upper and lower stone for heat reflection. I got the dough pretty well dialed in and friends are always bugging me to have a pizza night (although I think the bottomless keg of homebrew on tap is also a draw).

But downloading the forno bravo pizza making pdf and oven guides got me wound up. I can build one, too, I thought. But not much budget here, unfortunately. Fortunately, I found this thread and the light went on.

And thanks to the many posts of DavidS, I realized I didn't need a big oven and a small cast was feasible. So the planning and research began.

tektonjp 09-14-2011 05:20 AM

Re: Economy 24" cast in place in Japan
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After a few evenings of planning and getting the size and location nailed down, I purchased the blocks, re-bar, and readi-mix.

It's a small foot-print, about 91 cm square. The finished dome would come right to the edges. After digging a trench for the footings, I mixed the concrete and laid in the bar. When the concrete had gotten a bit set, I placed the first row of blocks in the concrete, squared and leveled the lot. Then vertical re-bar was stuck down at the corners. I decided against buttering the joints, etc, and basically did a dry stack with filling about half the cells with mortar. It all went quickly.

tektonjp 09-14-2011 05:28 AM

Re: Economy 24" cast in place in Japan
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After notching the blocks for the cut scaffolding pipes, I used a piece of durock which had been hanging around my shop for years, just waiting for a chance like this to shine! I made a plywood form to hold the vemiculite base in place. And to hold the form in place, as the vermiculite would come to the edge, I slipped some old pieces of roof flashing under the durock to hold it temporarily (see, honey, that's why I never throw any thing away!)

I got my first verm at a home center and the particles were rather small and I ran out quickly. Off then to a nearby garden store 'voila', big bags, big particles, and less money. Happy ending. I think I mixed this at about 4 or 5 to one. Look closely at pictures and you can see the stratum (sp?).

tektonjp 09-14-2011 05:45 AM

Re: Economy 24" cast in place in Japan
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So, with about a day and of half of time and maybe 5,000 yen (60 US) into the base, it was now time to head back to the shop. The base needed to dry and I would need to lay out and cut the bricks for the floor and the arch.

I drew a diagram on a thin piece of plywood and laid out the hearth bricks and the diameter of the floor bricks. I then made a quick copy of the lay out which I could lay over the bricks to mark them for cutting. I placed the bricks on the pattern, scribed and numbered them. I was surprised I only needed 15 refractory bricks (#34) bricks for the floor. Four regular for the hearth and 9 for the arch.

I originally thought I would be able to use my newly contrived DIY tile saw for the bricks, but alas not enough clearance. Break out the grinder. But since I had the water tub out, maybe I could collect some brick dust, I though. Getting a rounded cut wasn't that difficult. I kept my pattern circle nearby and that helped me put the arc on the back of the brick as well.

Those done, I used a cinch belt to draw them together before laying out the arch. The arch is definitely not an architectural triumph, but it gets the height and width right. Hopefully, it will remain standing. The first two are just flat, then I eased the edges on the remaining so that the final keyway would fit just right. I used a work form to hold every thing in place. Don't forget to leave spacer blocks under this!

tektonjp 09-14-2011 06:04 AM

Re: Economy 24" cast in place in Japan
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Onward to playing in the sand!

I thought the easiest way for me to keep the base of the sand castle under control was with some kind of form. I'm a furniture maker and on occasion have used bending plywood in my pieces. I dug out a scrap of that, ripped it to ten cm wide. I then cut another template of the floor, this time in half inch ply, and then cut it down the middle, as this would go down over the floor bricks and under the sand, and would have to be removed through the door. This piece was also cut 12mm (half inch) less than the radius of the floor so that I could bend the bending ply around it for a nice curve. I covered the bending ply with packing tape so the concrete would release. Finally, the two ends of the bending form end right at the opening of the arch. They are held together with a 2x4 which has angles cut to hold it just so. And I remembered to even "pre-cut" the center of the 2x4, leaving only about 1 inch holding every thing together. This should let me cut this away easily after casting and then be able to get the bending ply out with out difficulty.

I used a number of old bricks to fill up space before adding sand. And even then, I think it took about 5 big buckets. I kept sprinkling water and packing it down. I used an empty can on top of the final brick to give me an idea of final height, and then removed the can and filled in the hole. The final shape was the most fun. But when it was done, it looked funny and unbalanced. Too hunch-backed. I got my level out and checked the height. Yep. Somehow it slipped away from me and grew. I had to shave several centimeters off and then reform the dome to get a nice shape.

tektonjp 09-14-2011 06:14 AM

Re: Economy 24" cast in place in Japan
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Last post for the night.

After getting the sand shaped, I needed some type of barrier to keep the sand from sucking the water out of the casting cement. I tried saran wrap. Wish I had some pictures of that! Then some dry cleaning bags. Seemed to work better, then I realized the casting would slip right off of it. Then I went back to the original thread which got me going, and he used newspaper and covered that in wax. Great. I have tons of left over candles in the shop (don't ask). Shred the newspaper in thin strips, dip in water, then place on the form. I only went maybe two layers over all, I think. I left that to dry for a day before doing the wax. I thought about giving it a Brazilian, but.... the wife was home. I didn't care too much how the wax left big fat runs down the side, so not knowing how much that might project with the concrete, I warmed up an old iron and flattened them out. Now, I wait for the casting cement to arrive.

david s 09-14-2011 01:10 PM

Re: Economy 24" cast in place in Japan
Good luck. Your base is exactly the same size as mine. I think you should have really done a structural concrete layer under the vermicrete, but as you seem to have it pretty well supported the vermicrete should be ok especially as the oven is small and won't be all that heavy.make sure that when you mix up your castable that you make it a stiff mix that will stand up vertically by itself. Do not mix up too much in one go especially at the start. The higher you go the easier it gets as the mix will be leaning in. Us a satay stick or piece of thin wire to use as a depth gauge so you get the thickness even. Looks like it's coming on really well.

robertjusher 09-19-2011 12:05 AM

Re: Economy 24" cast in place in Japan
I am thinking of going the same way so am keen to see how you go, good luck !

Lburou 09-19-2011 07:56 AM

subscribed :)
This is an interesting build. Might use this method for my son, on a portable base. :)

david s 09-19-2011 12:29 PM

Re: Economy 24" cast in place in Japan
If you are making up your own castable mix it is advisable to add some fibres that will burn away to leave mini tubes that the moisture can escape through. This helps prevent blowing during curing. Proprietary mixes contain these. The easiest way is to add some animal or human hair which can easily obtained from a barber or animal grooming business.

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