#1  
Old 05-27-2007, 06:35 AM
Peasant
 
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Location: Australia
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Angry Dome collapse - advice needed

Help please

I thought I was going well with my dome construction (see photo at http://www.fornobravo.com/forum/phot...ndex.php?n=286) until I went to finish the top half and
1. It looked like Noddy's hat.
2. It collapsed when I took down form.

I reckon my problem is that each of my layers were flat topped (oven inside brick face always 90 degrees to oven floor) creating a stepped effect with each layer. Am I correct in thinking that after the first layer these should start to tilt towards centre of oven? If so, is it best to use a wedge of mortar or brick wedges under second layer to get this going?

A dejected but not beaten Steve
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  #2  
Old 05-27-2007, 11:16 AM
Dutchoven's Avatar
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Default Re: Dome collapse - advice needed

Yes, definitely should have a bit of roll to each succeeding course. That way the weight of the bricks is thrusting out toward the bottom course of bricks. I think you can begin with an angled first course in a soldier pattern. That will "spring" the angle for your dome. You should then be able to use a removeable shim that should prbably taper from about 3/8" to 0" you can then set the mortar alongside the shim and tap your brick into place, then when you remove the shim you can back fill the space with mortar. This method would get you most of the way up in your dome without forms, that is until gravity takes over. It will also help to make sure that you have a bit of a "keystone" that will lock each ring in place.
Hope this helps.
Dutch
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Old 05-27-2007, 01:49 PM
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Default Re: Dome collapse - advice needed

I recommend laying out a test "slice" on table or board. Since I was building a 42 dia oven I took a scrap piece of plywood and drew a 21 inch (half of 42) L with and T-square and then made a 21 inch arc to connect top and bottom. If you want a flatter arc then draw whatever shape you want. Then you can lay out your bricks and see how they have to be positioned to follow the arc. You could also use it to see what size wedges you will need, but you don't have to get that fancy unless you want.

I have a digital smart level. From my board I was able to work out that each course would be +7.5 degrees. So I took whatever cut wedges I had lying around the saw and pushed them in however needed to make my 7.5 degrees. Once I got the hang of it I only needed to measure the first brick of a ring and every 5th or 6th after that.
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Old 05-27-2007, 06:38 PM
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Default Re: Dome collapse - advice needed

just adding to what has bee said so far, Steve....

Yes the top of brick must be angled in as you go up. It is a bit tricky getting them into the right wedge shapes. I cut most of mine (solid red clay bricks) with a bolster and then chipped off the odd bit with a brickys hammers (long flat pointed end). You can always use a small grinder with a diamond blade or a brick saw but with this sort of brick its possible with hand tools...yet tricky.
How are you doing that last top bit......are you building a sand cap inside (just top half) as a support for the top section of bricks?

The other trick is when to pull out the dome cap formwork(assuming you use one) after you have laid up the last bricks. Sure if the bricks are interlocked properly it should stay up but its not always that simple (as you know). I found mine took about 2 hours of drying time. The mortar was fairly firm yet still had enough give in it - in case you had to make any adjustments from inside OR when you are removing excess mortar and cleaning up inside with a sponge etc.

have a look at some of my pics here:
http://www.fornobravo.com/forum/f21/...highlight=roar (The "Redgum Roarer" - brick dome oven)

you are nearly there....
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Old 05-27-2007, 06:57 PM
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Default Re: Dome collapse - advice needed

o yeah....if you are going to join the dome with the front arch get some brick ties in to get the two to bond together. Usually AUS$0.45 ea at a local landscape supplier, building supplies or larger hardware.
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Old 05-27-2007, 07:42 PM
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Default Re: Dome collapse - advice needed

One more tip myself.

Did not have any problems with the bricks staying put till about the 6th course. Wanted to keep things simple, so used short 2x4's with a nail in one end to catch the brick face and keep the brick in place. Then it hit me, why not move the floor? So, I cut a piece of my pink foam board to be exactly the same size as the top of the complete ring. Then got a small scrap square of plywood and drilled a hole in the center of each. I have some long all-thread and with a nut and washer wallah, a jackscrew if you will. So that propped up my "floor" and simply place bricks in place. When you finish with one ring simply cut the foamboard down to the next size and repeat.

Not saying it is a better way, just a real easy way that worked well for me.
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Old 05-27-2007, 08:48 PM
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Default Re: Dome collapse - advice needed

Um, how did you get it out?
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Old 05-27-2007, 09:01 PM
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Default Re: Dome collapse - advice needed

Well Wade all I have to say is you have some fantastic ideas man. Definitely an out of the box thinker. I am glad you got in the plywood form as I forgot to mention it. Cutting each brick works very well also and keeps mortar joints nice and thin, could almost dip them. Cutting would be very tricky and I would suggest saving the cutting for the sides to make them fit nice in each ring and take care of the roll using mortar.
Best of luck
Dutch
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Old 05-28-2007, 12:22 AM
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Default Re: Dome collapse - advice needed

Steve,

I noticed in some earlier photo's on your photostream that you fabricated a dome gauge, as per Russell Jeavons' suggestion. This theoretically makes it straight forward to get the angles right for the second and subsequent courses, right through to last couple of rings or so.

See page 19 of Russell's book for a diagram of how the dome gauge is used, course by course. I have no experience with using a gauge like this, nor will I, as I'm using tapered bricks which should form a natural arch by themselves (fingers crossed!).

As for the last few rings, I like Wade's brilliant idea of using a reducing circular template to support the bricks in each course - I'll definitely be trying that one myself!

Cheers, Paul.
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Dome collapse - advice needed-russells-dome-gauge.jpg  

Last edited by Hendo; 05-28-2007 at 01:47 AM. Reason: Added pic
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Old 05-28-2007, 01:04 AM
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Default Re: Dome collapse - advice needed

KISS4me - I'm looking at your "Dome mold" photo, it looks like you are going by Russells suggestion - As Hendo rightly alludes to.

What I found is I didn't bother using mortar (cement) in the mold mix (Russell suggests mortar). I just used brickies sand which is coarser and has clay in it. Dampen it enough and it shapes fine and holds for a few days. It's easier to clean and you can reuse the sand if careful.

With laying the bricks....
We (Brickie mate and I) found instead of buttering the bricks and then putting them down, put them down first - angle the back of it up and "flick" in your mortar from the trowel. Then with a rubber mallet give it a small tap - down and up against the adjacent one.
We only ended up cutting the last one in each circle (course) and on the last circle it got tricky.

...mmm.....hope this helps....sorry if you already know this....Iím keen to see you succeed.


Hendo.....I'm guessing even with tapered bricks you would need to build some sort of mold to hold it(or other method). As there would be a point where each top course (ring) would want to slide in due to gravity. Sure once the dome is up it would all hold up. Same principle as a brick archway.

Best thing someone said to me was "Its a brick oven - not a mortar oven"......then it all fell into place - oooopppsss no pun intended KISS4me
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