Economy 24" cast in place in Japan

[tektonjp]

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 http://www.fornobravo.com/forum/f43/...oven-9380.html 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]

Re: Economy 24" cast in place in Japan

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]

Re: Economy 24" cast in place in Japan

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]

Re: Economy 24" cast in place in Japan

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]

Re: Economy 24" cast in place in Japan

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]

Re: Economy 24" cast in place in Japan

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]

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.
Dave

[robertjusher]

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 !
Rob

[Lburou]

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

[david s]

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.

[tektonjp]

Re: Economy 24" cast in place in Japan

Thanks for the advice, David. I really couldn't locate the fireclay to make this a really cheap build. In the end, I decided the casting cement made by Asahi seemed to be an easy route to follow. However, the price has gone up drastically in the past year or so, but it still fit into the budget for a cheap bill, so I plopped down some money for the casting cement, 4,500 yen per 25kg bag. My original calculations were for 3 bags. I did a rough figure of the inner and outer sizes of the domes as half spheres and respective volumes, and a desired thickness of 5 centimeters gave me a certain amount of liters. The manufacturer's site gave a rough shot of liters of mixed material per bag and so I ordered three. But the nice upshot of it was..... in the end I used two and the third is now in storage for a planned, even lighter, portable one done the same way, but with insulation bats instead of vermiculite on top. But that is a tale for down the road.

I was lucky to have a buddy come out the day I picked to mix up the casting. Asahi makes two types, one that is "packed" on, worked by hand into a lathe or similar, and a second type which is for troweling. I went this way and that, use mesh or not. I checked with the masonry store, and the owner confirmed what I hoped, that a small dome like this one would be okay without lathe or mesh, so I went with the trowel type.

Of course, that didn't mean we started with a trowel. IThe hard part would be keeping the depth consistent. We opted to maybe kill two birds with one stone. We would set the final thickness on the base to about 10 cm high, and hope that would give a good foundation for going higher in thinner coats since it seemed so vertical, and a determined thickness would give our eyes a reference as we went up.

We ended up do a combo of packing the cement on by hand and then troweling it out. Packing by hand allowed us to do a slight vibrating action which I think let a new layer blend in well with the previous. We worked quickly, almost too quickly because we often needed to wait to let the mud set up some so the next layering wouldn't make it set from gravity.

Still thinking that some sort of "aggregate" would be beneficial and stainless needles not handy, I lugged out a box of old screws and we pasted those in all over the place in the under layers. Not sure if we were just playing or if this might help, who knows.

The next day the sand form was dug out. The instructions said the casting was good to go in 6-8 hours. And it was. The wood forms came out perfectly from inside and our vibrating trick seemed to give a nice smooth interior finish as well. No cracks and sounds sturdy.

Day after I built the curing fire. Again the instructions were simple and easy. One fire with slowly rising temperatures, a rest at 200c and 300c, altogether 5-6 hours, and finished. Very easy and no problems.

[tektonjp]

Re: Economy 24" cast in place in Japan

With the casting cured and looking good, it was time for the vermiculite. I really enjoyed this part. It's fun to mix and fun to slowly watch the shape take place.

I mixed it at about 8 to 1. I found it easiest to throw the V into the mixing bed (a huge plastic box), dampen it slightly with a garden watering can while mixing it up with my free hand. Then, sprinkling in the cement while doing the same motion. After adding all the cement, a good mix by both hands, then again sprinkling little by little with the can until the mix is just wet enough to hold together and set the cement off. I probably used about 90 liters of V.

I followed the same pattern as the casting, setting a base row and working from that. But I approached the top, the curve looked like it might through my thickness off visually, so I put a row of insulation on the top to give me something to work toward and keep the thickness the same over the curve. Hence the photo which looks like a mohawk!

Up to this point, I have spent about 30,000 yen (360 US maybe?). The only items which I didn't pay for were the scaffolding pipes and the durock board as the base. I think I have managed to make this a real economy build and I hope others give this a shot.

[tektonjp]

Re: Economy 24" cast in place in Japan

After a week of air drying, I fired up the stove to dry out the insulation layer. I got a beautiful fire going, and it cleared the inside of the dome wonderfully. The vermiculite steamed away. And of course I got some good cracks in the V, but I think that is to be expected. I will follow David's advice (on another thread elsewhere) to have a number of firings before doing a render. So hopefully I'll have the final photos sometime later this fall.

Thanks to everyone on FB. Great place to learn and I hope my little experiment gets others thinking too.

[robertjusher]

Re: Economy 24" cast in place in Japan

Top oven, been thinking of going that way but a little bigger and casting in place but with thin ply to seperate the pieces to make it a 4 cast piece oven.
I will keep watching.
Rob

[Manolo54]

Re: Economy 24" cast in place in Japan

I am planning to brush a solution of starch on the newspaper and let it dry to provide the moisture barrier for the castable. Am thinking it would be easier to burn off as well later...