Tims oven - early days!

[Tim F]

Re: Tims oven - early days!

I got the forms up and poured the slab on top after work yesterday. It's not the nicest bit of concrete ever poured, but it's level at least!

I tried to stop the forms from bowing by running a rope around the stand and wedging planks along the sides of the form. This wasn't enough, and I ended up with a 2-3mm bulge along the middle of the long sides. I think I'll be able to clean it up with an angle grinder though, and none of the slab will be visible in the end. Any thoughts?

Tomorrow I'm off to get the insulation for under the cooking floor, and I might even be able to start on the dome this weekend! Any thoughts on the easiest (& cheapest) way to make a round form?

[Tim F]

Re: Tims oven - early days!

And a couple more - I swapped the forms around the sides of the arch, poured concrete, let it set, then took the forms off. Then I got the cement board in place, I had to cut a little notch to fit it around the top of the arch. I stuck a strip of duct tape across the joins in the board. Once that was done, I laid a grid of rebar, using the ends of the vertical bars in the stand as spacers. I tied the bar together and now I'm almost ready to put up the forms!

[Tim F]

Re: Tims oven - early days!

Now that the mortar is in I think you are right, it looks quite nice. I've started to scrub the bricks clean with some dilute acid and they are coming up well.

I finished off the arch, yesterday. Lessons learned - it would have been a good idea to lay out my arch on the ground first, and mark off the position of where the bricks should go, so I could see if I was getting a bit off track. My biggest mistake was relying on eyeballing each brick instead of checking each one was flush with the others across the front of the arch. By the time I got to the keystone I was about 10mm out! I managed to fix it by pulling off the previous 2 bricks and mortaring them back in at a slight angle, and cutting a slight slope in the keystone brick with the angle grinder.

This morning I cut my cement board into the right lengths to cover the stand. I cut it by scoring it with a tile cutter, and then holding down a long screed (but a plank would have done it) just behind the cut, and slowly lifting the section I was cutting off the ground. I found that if I didn't do it this way, it didn't break cleanly across the score.

After that, I cut out a form to pour some concrete in the space between the side of the arch and the wall, to support the finish later on. Once this has set a bit I'll reverse the forms and fill the other side too.

[egalecki]

Re: Tims oven - early days!

I actually think your arch will look better with mortar than without. I just like the way bricks and mortar look together. When you build a dome without mortar, it's not a decorative thing- it's a purely functional thing. While your arch is functional, it's also decorative.

Maybe I'm just stuck on what I've always seen, but I do also like the way dry-stack stone looks... so at least I'm not just a mortar maniac!

I don't have a header across my opening either, but it's on a corner and not as wide. Be sure to use plenty of rebar across the front of your slab- that oven's one heavy critter.

[Tim F]

Re: Tims oven - early days!

Today I made a start on actually mortaring in the arch bricks for my stand entry. Unfortunately after a few attempts I decided that cutting the bricks for the arch to the 5.5? angle required for them to fit together without mortar was beyond my brick cutting skills at this point But I think they will still look ok once the mortar is cleaned up!

I tied the verticals in my arch into the stand by drilling holes in the besser blocks and tapping nails in so that they poked out between each brick, before I added the mortar - figured it couldn't hurt.

I got the cement board and rebar delivered today, so I can set up the forms and pour my next slab as soon as the arch is finished.

[Tim F]

Re: Tims oven - early days!

I'm actually making a brick arch in the opening, more for decoration than anything else although it should be able to support quite a load. But if you are pouring a well reinforced slab, I can't see why you need the extra row of block across the opening. If anything, you could just sink the same bit of angle iron into your slab and get the same strength as if you had it underneath with a row of blocks on top!

I'm doing exactly as you said - laying concrete board (Hardirock) over the opening, so it just overlaps the block. The concrete board will be held up with forms inside the stand, and my plan is that the slab will tie in with the rebar that I have left poking up out of the stand as well as the rough top face of the blocks. I'll post pics as I do it!

[Dino_Pizza]

Re: Tims oven - early days!

Your block stand looks great Tim. It appears you have a front opening, open all the way to the bottom of your concrete hearth base. Iv'e read about others recommending that. Is that what you are doing? Do you just lay the concrete backer-board across (& overlapping the edge of the blocks) and pour the concrete on it, with a form? or is there anything else spanning that opening. I'd like to forgo the angle iron and row of block too. I'm about ready to dig my footings and your design interest me. Good luck on it!
Dino

[egalecki]

Re: Tims oven - early days!

It looks good. I think Ken may have a chart on his thread he did with heat retention over a period of time- that may help you, if you can find it.

For me, the motto was "more is better" for insulation, so go for as much as you can fit on there!

[staestc]

Re: Tims oven - early days!

Nothing better than a mock up. Looking great Tim!
Travis

[Tim F]

Re: Tims oven - early days!

One more photo for tonight. I really wanted to see the arch in place so I mocked it up using some shims to hold the bricks in place.

[Tim F]

Re: Tims oven - early days!

Thanks for the link, I hadn't really considered the need to have such a hard surface to render over. The more I think about it, the more I think I might just use castable insulation - but I am trying to figure out the equations around heat conduction to see how much I would actually need to achieve a certain heat loss per hour (any ideas what a good target would be?)

Progress has been slow the last few days as I have been thinking about some of my design concepts. I am making an arch in the stand opening, and weighing up how I want to fit the brick around the form. I have decided that I would prefer the look if I tapered each brick so that they fit together without mortar, so I am making a jig for my saw to hold the brick at the right angle. If it turns out to be too difficult to get the cut exactly right, I will just go with the bricks un-tapered and mortared together.

I've got the supports up inside the stand, and filled the cores with rebar and concrete. I'm going to lay a piece of cement board so it just overlaps the inner edge of the stand, then pour my slab on top of that - hopefully this weekend.

[dmun]

Re: Tims oven - early days!

I think there may be a product you can use to harden blanket, but I am not sure, and I don't know if it changes its effectiveness if you use it. If it exists.

Here's the stuff:

Refractory coating Rigidizer for Ceramic Fiber Blanket - eBay (item 140275551619 end time Oct-23-08 06:56:22 PDT)

I don't know anyone here has used it on dome insulation.

[egalecki]

Re: Tims oven - early days!

It's not the amount of insulation you have planned that's the problem, it's getting the dome successfully covered in something hard enough to stucco that's the problem... I don't know if you can stucco directly on the blanket, and I don't know if you can put on a layer of vermicrete as thin as you're talking about.

I think there may be a product you can use to harden blanket, but I am not sure, and I don't know if it changes its effectiveness if you use it. If it exists.

[Tim F]

Re: Tims oven - early days!

thinking some more- you could actually extend your form past the edges of your stand a bit- if you use enough rebar you'd be fine- that would maybe give you enough room to fit what you want on there without it being a problem. A couple of inches on each side is all you'd need- I'd build a form with legs, using concrete backer board to support the extended part. You could just leave the backer board in place later.

All interesting ideas. I have mulled over extending the slab beyond the stand a little bit but it is in a pretty tight spot already. I was kind of thinking that 3 layers of blanket might almost be enough on it's own - am I wrong? The other alternative would be to put a thicker layer of castable insulation straight on top of the brick. The one I'm looking at has very similar insulating properties to the blanket, and I'd have room for 40mm or so of it. Then I'd use 2 layers of blanket. I'm just not sure about how easy the castable will be to work with - I will find out soon though, as I've decided to use it as the insulation underneath the oven.

I have also thought about an enclosure as opposed to a dome but I really like the look of the dome and want to keep it if at all possible. It's difficult to find the right compromise between form and function sometimes!

[Dutchoven]

Re: Tims oven - early days!

...erm, that was heavy breathing like Darth Vadar does... You know, his scuba diving impression? And then he goes "impressive, very impressive, but you're not a Jedi yet." One of my favourite scenes, that is.

However, I will admit you could well have been right, Dutch.

I knew the scene...I have just been a bit playful these days
Best