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Lars 06-05-2009 07:33 AM

Arch buttressing.
I am building my way through the questions that arise.

So far, my three main questions have been about the mortar, the doorway, and, in my case, the arch vent.

I suspected my arch might have too much lateral force on the stack of four firebricks on either side of the vent/landing area. When I built it, I noticed the left stack had shifted. UGH!

Provided things are still standing after the mortar sets ( I am using portland/fireclay mix -- which does not seem to provide significant bonding strength) I am thinking of using regular solid bricks on either side to help support the lateral forces of the arched firebrick vent. ... then go on up with the bricks ( weight transferred down) to hold a chimney section in place over the vent.


Les 06-05-2009 07:49 AM

Re: Arch buttressing.
1 Attachment(s)

I didn't encounter any problems but I had the same concern. I dropped in a few pieces of steel and used cored brick. They can offer more strength then the solids you are considering.

DrakeRemoray 06-05-2009 09:17 AM

Re: Arch buttressing.
Make sure you fix the leaning bricks on the side. This happened to me too (I think it was just my shoddy brickwork) and I did not fix it. So now my opening is slightly smaller at the top than at the bottom and it caused problems with the trim piece I put on the opening as well as being problematic with the door. It just made it very tricky to build a door that would fit and it makes it difficult to get the door on and off...

I wish I had fixed it...

egalecki 06-05-2009 11:24 AM

Re: Arch buttressing.
I stole from Les- I drilled into the hearth slab, set rebar in, and used 3 hole bricks on the sides (with lots of mortar in the holes around the rebar) to buttress my arch sides. It's worked great.

Bandrasco 06-06-2009 04:55 AM

Re: Arch buttressing.
I think that Les' approach would be the most fool proof. In my case I didn't add any additional bracing. The flared arch entry is holding strong along with the solid bricks and double arch I created. I used standard type S brick and block mortar for the Chicago bricks and so far no movement. I thought of sinking a few rebar's in the hearth but my design spread the weight load over such a wide area I was confident that it would support it. I do however believe in the rule 'more is better' (in most cases) so if you have the time and materials to add support I'd do it.

Good luck!

Lars 06-06-2009 05:17 AM

Re: Arch buttressing.
My vent arch still stands, but I wouldn't set a bucket of mortar on it!

I added chain #7, and if it weren't for this tricky mortar ( which has no reliable adhesion component) I would just sort of 'continue' the arch on either side of the four brick stacks. ( since it is at hearth level, it really is like a 'flying buttress!' )

Unfortunately, in my mind's eye, I see the mortar joint breaking because it would not be perpendicular to the arch, as it were...hmm. With any weight on the arch, I just don't see it holding.

When heat comes into play, things have a tendency to break loose!

I will take some pictures and post them..

Lars 06-17-2009 08:33 AM

Re: Arch buttressing.
3 Attachment(s)
Using the ideas from this thread, I think I will have solved my arch issue, and here are the pictures.

I am building a 39" inside dome with a stucco/dome exterior. The bricks around the opening arches are one step larger than the 'weak' outer, vent arch ( vent arches are one step larger than oven opening). I double arched it, using tapered bricks on their side, so the final arch sits out about 1/4" from the wall face.

( I thought there might be a time when one would want to close up the oven on the front side, outside the vent opening--perhaps while firing, or to put a permanent door on to lock it up when not in use)

Anyway, the house bricks ( which I got to match the firebricks...$0.25 apiece) use strong portland mortar, and, for the most part, do not physically contact the firebrick front arch. They wrap around the sides, then angle back at 45 deg. along with the lines of an outer dome.

This configuration should give it a real excellent buttressing ( I connected the arch to the brick wall with mortar at around the shoulder of the arch -- where the lines of force would continue --lateral forces)

Next step, I am off to Lowe's to buy a sheet of metal lath. I will calculate the difference between a circle 5' diameter at the 'equator' of the dome, and a circle, say 15" up, and try stretching my metal lath and see if I can approximate a spherical shape... then attach that between my brick, 45degree, corner walls. --- may not be too spherical when I am all done.

My thought is that once I get the almost vertical sides filled in, I will make a 5' diameter arc trowel ( out of masonite) and use that to tamp the vermiculite layer in place.

Lars 06-20-2009 07:36 PM

Re: Arch buttressing.
Yesterday and today, I made batch after batch of vermiculite/portland.

The oven has 2.5" of vermiculite/Portland that it rests upon. I had a shortage of space around the dome, so I was able to 'hang over' about 2" on the sides and back. I basically used about 4" of vermiculite/Portland up about 10" around the dome. From about 10" to 22" I put 1" ceramic blanket, held in by 4" of vermiculite, then metal lath and stucco. At the crown of the dome I plan to use 2 to 3" inches of ceramic blanket held in by the vermiculite/Portland.

Before I enclose, though, I LIT MY FIRST FIRE! I burned up a cardboard box and few slivers of wood. Couldn't even feel any warmth on the top of the dome bricks.

I got a few puffs of smoke out the door, but I did not have my flue up there. I think sealing the flue will help create a little draw. Is that true? ( open question)

So, I am on the one stick, two stick, path!


Lars 06-23-2009 07:52 PM

Re: Arch buttressing.
1 Attachment(s)
Third curing fire, bricks warm on top!!!

I would like to know what everyone thinks... my flue section is basically just resting on top of my arch vent for now. Do you think when I seal it up it might draw better? ( I will look for a photo to attach) I am getting quite a few puffs outside the vent ( out the main opening)


Les 06-23-2009 09:06 PM

Re: Arch buttressing.
It will obviously help a little. When the gases reach that point, they are trying to get the hell out of dodge. When you see the smoke, is it the initial fire or after everything is reaching temp?


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