Starting my build

[david s]

Re: Starting my build

Good point. A removable flue is a good idea for a mobile oven. You don't want a flue flapping around while traveling. I made a sleeve in stainless that my flue slides into. My flue is quite tall as I didn't want smoke to be a nuisance to other market smallholders, so I'm glad I built it this way.

[oblertone]

Re: Starting my build

Your flue pipe is part of a system that join together to make a fire vent although you're only using one piece; part of that system will be an anchor plate so speak to you're supplier. If you get one then just cast a flat surface and bolt/bond it down.

I did this to make my flue demountable as my oven is moveable, but hopefully you'll get the idea.

[david s]

Re: Starting my build

Re the voids, I meant voids on the inner surface of the dome. If you can't get to it and the newspaper is covering it anyway, then just leave it. It is largely a cosmetic thing.
Re the flue gallery, i'd be blocking off the hole with a large ball of screwed up newspaper, then making a sand mould on top of it, then make up your castable and build up the casting around the sand and the pipe. If you wrap some thin cardboard around the pipe first it will give the pipe some expansion room. Also wrap two layers of plastic around the cardboard and the pipe will slip out easily. When making the sand for the casting use 8-10% water by volume and add a little powdered clay. Make sur you clean any sand off the surface you want to join to.You may be asking for trouble drilling and screwing, the mix should bond well enough to the previous casting.

Regarding an extra layer on the outside, only do this if you want extra thermal mass. Most commercial cast ovens are around 2" thick. which is plenty for cooking bread or a roast. If you want to bake bread for the whole neighbourhood you may want it thicker, but that also means longer time to saturate the oven/ fuel consumed.

[almondsurf]

Re: Starting my build

I was thinking about drilling / gluing some screws into the flue gallery cast, then try casting another 6" or so (hoping the screws would bond with the new cast to keep it in place) around the permanent flue and screws. I just need something to hold the flue pipe in place. I am nervous about drilling into the cast as it may crack the whole thing???

Any help from anyone would be greatly appreciated. I am overjoyed with my current predicament.

[almondsurf]

Re: Starting my build



I am a little upset at myself for letting this happen. The metal pipe was meant to be a form for me to cast about 1' of the flue around it, then I was going to pull out the metal and put a finished flue on top of the 1' cast. As you can see in the pictures, that didn't work.

My problem was I casted the gallery/entry, then casted the oven area, then went back to cast the 1' flue ... By this point the flue gallery cement was apparently too dry and didn't bond well enough to hold the flue cast. When I went to take the metal out last night (the pipe was oiled down during casting so as not to stick to the cement mix, but stuck anyway) it just came right off. I was trying to pull out the metal, exerting a decent amount of force upwards, and... Poop! The whole thing came off.

The rest of it looks pretty good, but the flue issue obviously kept me up last night.

Question:
Does anyone out there have ANY Idea how I can possibly get a flue pipe to stay on this thing now???

[almondsurf]

Re: Starting my build

So... I kept the cast under the tarp all week. When feeling the outside of the oven, it felt rock hard. It was cool, but I assumed the cement had bonded, so I thought I was in good shape to remove the tarp and dig out the sand form. So at 9pm last night, I began the digging.

Chip:
I didn't wet down the outside because I read that it isn't good for the moisture consistency of the mix. I think the moist sand under the mix helped it stay cool and set slowly. Glad that helped. I don't see any cracking (like I did on my base).

David: (so many good points)
1. Yes, Yes and Yes... This is something I know more now after having it dug out what you are talking about. My reason was to get the smoke out of my face, but now I see it is going to be much harder to work the pizza. oops.
2. I never even though of this but after I was done digging, I sat there scratching my head last night thinking to myself... "how the heck am I going to make a door for this thing." Oops.
3. I figured I'd just burn away all of the newspaper since there is no way I can reach back in the dome anyway.
4. Well, the sand is already dug out... Not sure if I should still moisten it down??? Is it too late? The outside seems bone dry. I cant see any cracks. I did put in a lot of the steel needles. Also, the wood was a little difficult to get out, but I'm glad I used a lot of small pieces, which made it easier.
5. I guess I don't have to worry about this any more (see post below with pictures)
6. Should I put on a thin outer shell of mix without any poly fibers or needles, make it like a spread around the oven at a thickness of 1/4" to 1/2" thick? I don't see any voids, but would that help those areas I cant see. I'm sure it would crack, but this would just be additional mass.

Tomorrow will have been one week since the cast, so it sounds like I took the sand out a little early. Oops.

[david s]

Re: Starting my build

Good job, a few points.
1. You have a very deep entry which means access to the oven will be more difficult.
2. Because you cast oven and entry in one piece you are left with no rebate to place a door against the oven opening. Fitting a door for retained heat cooking may be difficult.
3. the four and water idea is good but it will make removing it difficult. just let what won't come off burn away.
4.Calcium silicate cements ideally need 28 days to achieve full strength. The addition of lime slows down the reaction so you may need even longer. Calcium aluminate cements need only 24 hrs. After 2 days you should be able to remove the form, but you might have trouble getting out that plywood. Keep the casting moist for at least two weeks.
5. if you cast directly around the stainless flue pipe, when it expands it will put great stress on the casting and maybe crack it. I cracked the first two cast ovens i did this way and now always leave some expansion room to prevent this. You may be able to remove the flue, ream it out a bit while the casting is still a little soft.(I did use double the thickness of pipe for those two cracked ovens than the standard ss pipe, so they would have much greater power when expanding, perhaps the thinner pipe might be ok, I just did not want to risk cracking more castings)
6. You will have some voids in the casting as vibration with this method is not possible. You can fill these easily (if you can get the newspaper off) by sieving out about a third of the coarser sand from the dry Homebrew and mixing it into peanut butter consistency. This will give you a richer mix and make application easier. This operation needs to be done before the casting has dried out too much, say a day or two after casting, so it will bond with the cast material. Just squish it in hard with your thumb and rub over the surface.

[mrchipster]

Re: Starting my build

I am no expert on casting but I would think you want to leave the sand in place of a week and mist the outside of the oven at least daily. As far as first fire two weeks from casting would be as early as I would think logical and longer if you have the patience.

Removing the sand and brick will help the drying process. Maybe put a fan inside after removing the core.

The flour water paper m?ch? idea was brilliant.

[almondsurf]

Re: Starting my build

More pictues

[almondsurf]

Re: Starting my build

Over the long holiday weekend, I managed to carve out my granite entry piece and put the inner dome together. My wife and daughter helped me along the way. A good wife is worth... well... everything. She kept saying, "I sure hope this is worth it." Inside I kept saying, "I sure hope I don't screw this up."

I thought this would be pretty straight forward, but of course, it was twice as difficult and took twice as long as I thought. The actual sand dome was pretty easy, but the sand flue gallery was more of a challenge. I started with the sand flue gallery; I don't think I had enough water in the sand as it was falling all over the place. I increased the water ratio for the dome and it went on quite well. I chopped up some old 2x4's as a filler so I didn't need so much sand. The newspaper was a (expletive) to put/keep on. The wind picked up and we had to replace all the wet newspaper about 3 times! Then my wonderful wife had the bright idea to make a temporary glue (1.5 part water, 1 part flour) to lay on the newspaper to hold it in place. This worked like a charm. Too bad I was over half done by that point.

I made a quick tarp pyramid the day before so I could have it slow dry to avoid cracking. Sorry, I forgot to take pictures of the final oven before I covered it. I added some mix about a foot up the flue (the pipe in the picture was just for a form for me to build up 1' tall around it).

I mixed the cement layer quite dry so I didn't encounter the "slumping" on the sides of the oven as other casters have mentioned. I think it was just enough moisture to make it bind, but not too much as to weigh it down (not sure the ratio). I'm going to leave it tarped for a week. I guess we'll see if all this worked.

Question:
How long do you guys recommend I wait until I dig out the sand, and for it's first small fire?

[NCMan]

Re: Starting my build

Looking good, almondsurf. Like you said, it didn't take long and you'll be glad you redid it.

[almondsurf]

Re: Starting my build

Thanks chip!! It was turned slightly clockwise. So that's what I did last night, put the puzzle together again. It's still not exact, but it's pretty close. Thank you again for your speedy reply.

[mrchipster]

Re: Starting my build

From photos it looks a little clockwise from where it should be. It will not kill anything but then again two more hours to reset is not that long to get what you really want.

[almondsurf]

Re: Starting my build

Question...

I placed my bricks on my insulation where I thought they ought to be (took about 2 hours because I had to level each brick).

I noticed after I was done that the front of the oven hearth is a little crooked / turned. The bricks are in the right spot, but the oven is just turned a little to the by about .75 inches (19 mil.)

Do you guys think I should relay these bricks to get it more exact???

The bricks extend about half way into the flue gallery, then I am going to cut a slab of granite today or tomorrow that will extend the rest of the way out to the front of the oven. I plan to cast the oven this weekend, so I need to move relatively fast if I'm going to take the time to redo the brick hearth.

[almondsurf]

Re: Starting my build

I thought I would post some progress I made today. I decided to go ahead and cut the brick using the circular saw. It worked out quite well (I think). I just soaked the bricks before hand for around a minute or until there were no more bubbles coming out of the brick while in the water. Then I used a clamp to hold the brick to a board and did my cutting. I didn't apply any water to the blade as the dust was relatively minimal. It did kick up a little dust though, should have used a respirator rather than the little $1 insulation mask I had laying around. I thought it was much better than buying or renting an expensive 10" tile saw.
I hope to be casting the oven by next week. My needles and blanket arrived in the mail a few days ago.

Notes:
-The fire brick in the pictures is not in its final location, I still have to put down sand and level.
Thank you for all of your help and suggestions so far!!!
-For anyone who tries this method, be aware that the bricks are a LITTLE more fragile after soaking them. Just something to be aware of.