~38" build in Seattle

[pluscwc]

Well, after many delays and much procrastination, I'm finally cutting bricks for the dome of my oven.
It's a little over 38" diameter, hemispherical dome, 19" x 11.5" opening.
4" of underfloor insulation, 2" of FB board and 2" of ins block-19.
I'm planning on using homebrew mortar. Thanks to deejayoh for giving me his leftover supplies last year.
The floor is cut from standard Mutual Materials firebrick, but for the walls I have slightly odd sized gray firebricks that were picked up off of craigslist from a residential fireplace dismantle. They are basically clean because the fireplace was constructed with two layers of bricks and I was the first one there to pick through the supply.
The plan right now is the enclosure will have a peaked roof, with an overly tall chimney, because the oven is located next to a covered outdoor space attached to the house.

I stacked the stand walls a couple of years ago. Then poured the hearth, installed floor insulation, and oven floor last fall, then mothballed the project until last weekend. I had weed seeds that sprouted in my oven floor.

As a side note, FB board and Insblok will mildew if left under a sheet of plastic all winter in the Pacific northwest. It's mostly dried out now, but I need to make sure it doesn't get soaked again if I don't have a roof on by fall.

[pluscwc]

Re: ~38" build in Seattle

I want advice on how far from the back to locate my oven opening.

I don't like spending too much time with CAD, since I use computers enough during the day.

Option A is closer to the center of the oven.
Option B is about a brick width further out.
I remember seeing variations of both of these. Is one better, easier to build, more stable? I am thinking A is too close to the center and I should recut my floor bricks to bring me back to B. (I was there, got convinced it wouldn't line up correctly and trimmed some of my floor off.)

I'm planning on having a thermal break, similar to deejayoh's.

Should the arch be deeper than the half-brick I'm currently showing?

[texman]

Re: ~38" build in Seattle

plus

you want option a with more brick for the arch. You need the arch to protrude from the dome to support the back side of the vent. If your IT is set up correctly, the option A is correct and will be easier to build, more stable and appealing (IMO). Most builders use a 3/4 brick for the inner arch (i think). Check out my build and you will see that my inner arch did not protrude enough. I made it work (Gulf did really), but would have been easier to use 3/4 brick or full brick for inner arch. Octoforno set the bar on an option A build, check that one out, too. Look for Lee's treasure thread for many quality builds for reference of the many styles of domes out there. You have many options! Welcome aboard!

[boerwarrior]

Re: ~38" build in Seattle

I 100% agree with texman.
I built mine similar to your option "B". I wish I had gone with option "A". I ended up having to cut some filler pieces of firebrick to fill in the gaps between my dome and arch.

My oven works great but it was a PITA to do that work after I thought I was done with the dome.

[deejayoh]

Re: ~38" build in Seattle

Hmmm - I think you want somewhere in between. About an inch of brick sticking out from the dome at the bottom, and you will have 3 or 4 inch overhang at the top - especially if you are planning a heat break with an overlap like what I did. As Texman points out, you are going to want to use more than a 1/2 brick for the arch. If you cut the back of those away at an angle, you don't have to cut any filler pieces like Boerwarrior mentions.

Here's a shot of what I mean


BTW, Glad to see you've finally got going on the dome!

One observation - how far back is the opening of your dome from the edge of your hearth? Looks like a long reach. If I had one thing to change about my oven, I would have made the distance from the edge of the landing shorter. I think mine is about 23" IIRC from the edge of the landing to the edge of the dome floor.

[texman]

Re: ~38" build in Seattle

another point:

Remember that if you taper the arch brick (like Octoforno) that arch placement will change. The brick in your IT will be lower than your current pics and would change your setup by causing the arch to move outward/away from the center of the oven to line up like pic A.

[pluscwc]

Re: ~38" build in Seattle

Thanks for the advice. I guess I'll build a mockup with beveled arch bricks.

I need to measure how much the reach is. At this point I can still move it. I don't know how much the insulation has bonded to the hearth. Hopefully it won't cause too much damage. If I recall correctly, I was planning on a 12" ledge at the front, but I don't remember what the vent depth was. All of this will come back to me shortly.

[pluscwc]

Re: ~38" build in Seattle

OK, right now with the projected placement (A with longer bricks) above, I have about 21" from the forward edge of the entry arch to the front of the hearth. How much closer would you make it?

I need a small gap for a heat break, 11-12" for the vent, and a decorative front arch?

I'm quickly running out of landing, but I guess that makes sense.

[deejayoh]

Re: ~38" build in Seattle

Just measured mine, it is 24". 21" is probably good - but remember you are likely going to want your landing to extend beyond where your hearth currently ends, just for appearance. Mine extends 3" beyond at the center of the hearth.

I think you can do your vent in 9-10", and the landing doesn't really need to be that deep

[pluscwc]

Re: ~38" build in Seattle

Saw this from brickie in another thread. http://www.fornobravo.com/forum/f8/l...rch-15779.html

"Underside of arch to intersect the underside of the dome no matter the size of oven or arch.
If you mess with 1 dimension you have to mess with the other."

Sounds like it's raining outside. I missed my opportunity to build a cover before things got wet again.

[brickie in oz]

Re: ~38" build in Seattle

I see from the pics you are using an "Indispensable Tool".

By using the arc of the tool you should be able to work out the oven opening arch to dome height, use some cardboard to scribe it on, it will help to visualise how things should go.

[pluscwc]

Re: ~38" build in Seattle

OK, I rebuilt things a little bit, since I'm still too dense to quite understand.

I think I want the arch bricks cut like the last picture, with 3-4" of flat top. The third picture has such a narrow wedge of brick on the inside that it seems likely to chip, and no flat spot on top unless I make it pretty long.

I don't think I can move the oven any closer to the front of the hearth without having to make some significant modifications to the roof above it for chimney clearance. With a 10" OD double wall chimney + minimum 2" clearance, I may already have to shave a bit off the roof. That's the correct size chimney, right?

I've also included a picture of my makeshift saw stand. A random piece of steel I picked up from work that had been part of a shipping crate for lab benches plus 4 casters and some scrap plywood and 2x. There's enough table behind the saw to hold a bucket of clean water for the pump. I cut a hole in the plywood under the drain plug, so when the tray fills up, I can rest a bucket on the 2x chunks in front, drain the water in there, and water my landscaping with dusty water.

I know I need to put some shims under my arch form, and make it plumb and a bit more stable. Any other advice before I start mixing mortar?

[Gulf]

Re: ~38" build in Seattle

Pluscwc,
What kind of firebrick are you using. The color has me concerned. I have removed brick that looked similar to those from behind the firebrick of old coal fired fireplaces. The brick I have were used as a type of insulated firebrick brick. They are heavier than most insulated firebrick sold nowadays, but not near as heavy as a medium density firebrick. This subject came up a year or so ago on somebody's build. I still have a pic that I posted on that thread back then. Sorry,but I can't remember the thread.

The bricks on the left are what I am referring to.



I hope that I am wrong.

[pluscwc]

Re: ~38" build in Seattle

Well, I checked the density before I picked them up and I thought it was alright. I just reran the numbers:

Mutual Materials standard firebrick:
9 x 4.5 x 2", 6.875 lbs
14.727 cubic inches per pound

My reclaimed brick:
8 x 3.75 x 2.75", 4.75 lbs
17.368 cubic inches per pound

If you molded my brick into a standard firebrick shape, it would weigh 5.6 lbs. It's about 18.5% less dense than the standard firebrick. I thought it was closer than that, so I'm glad you pointed it out and I checked.

Other than density, how can I test it? Build a drystack mini oven and put a fire in it? Any tests for abrasion/spalling problems?
Lower density will mean what? Lower heat capacity and retention, maybe more fragile?

I don't mind buying more brick if this is a concern, I'd rather build once and the brick doesn't drive the total build cost that much.

[UtahBeehiver]

Re: ~38" build in Seattle

Plus,

See if this helps with visualizing a tapered arch and helping you with the arch placement. http://www.fornobravo.com/forum/8/oc...tml#post111125