The Dragonfly Den in Retrospect, June 2009-May 2012

[SableSprings]

So, in order to create the look of a half-barrel oven from my short beavertail dome, I needed to add a barrel facade. I could only imagine doing it in brick, but I didn’t want so much weight on my stand. I decided that I would cut bricks lengthwise for a brick barrel classic look. I thought the easiest way to approach this would be to place a piece of cement board on each side, up to the halfway point where the barrel started to curve over the top.

I cut some hollow bricks lengthwise and used them to set the cement board vertically against the oven sides. Once I mortared these base bricks into place, the actual laying of the barrel walls was pretty easy to do...just set each brick half up against the board and presto -- straight & perfectly vertical . I did put in a few little pieces of pink fiberglass between the perlcrete sided and the cement board to allow for a little air flow (and to allow a little expansion room for the contained dome...if necessary during firing).

When I got to the top curve, I put some pink insulation over the top to act as a cushion and to let some air flow between the oven and the brick facade. I inserted some metal lath between the perlcrete and cement board. The lath was curved up and over the dome where it went into the other perlcrete/cement board. Obviously, the front and the back of the lath needed some extra support where the dome curved down (and the barrel would not )...a couple of brick chips strategically placed did the trick.

Once I cut the single line of bricks to start the top curve on each side, I was simply planning to alternately lay split brick courses up from each side. Hopefully I'd meet in the middle up on top and not have to cut slivers of bricks to "span the gap" (also the top I figured would be where the joints would be least visible).

[SableSprings]

Cart frames fit nicely into the stand bays, so I took the frames back to the college to have the tops, ends, and handles welded on.

Now that the oven was under the permanent, roofed structure -- I removed the temporary, first winter cover. On the left side of the oven stand, I had to do a minor fill. When we poured the top slab, the left side form board started to move out and the Ready-Mix operator "tapped it" with his hip to put it back over the blocks. He just tapped it a bit too hard and it was only a cosmetic fix that I made here.

I wished I had removed the temporary roof before we enclosed it in the den...certainly was a lot more difficult doing the demolition at this point. Next I needed to figure out the easiest way to turn the exterior dome into an apparent half-barrel shape...time for more pencils, paper & beer.

[SableSprings]

Bought 12' sheets of metal roofing for the den structure. Put roofing asphalt on the roof plywood and then used screws to attach the metal roofing sheets. I considered having some custom flashing made for the chimney (estimate of $200-$300) but ultimately (being extremely frugal) I just cut pieces out of some extra material to guide water away from the chimney opening. During the build I continued to work on baking bread in the oven.

Ripped some tongue & groove cedar pieces from a neighbor's house for insect screen frames. Stretched screen from 48" wide rolls across each window frame, cut, and tacked into place with hardware staples. After the screen was secure, we screwed the cedar pieces into the frame outline and in doing so, double anchored the screen panels. The French Doors were done in two pieces (top & bottom on each door).

The Umpqua Community College (UCC) welding instructor I’d contacted about building carts for the bays returned my call and said they had the bay cart frames ready to "check for size". I borrowed a pickup and brought the two carts home to see if they fit (or more correctly, if I'd measured it right). The carts are a student's final project in the class, so it's really a nice dynamic with getting everything "perfect".

[SableSprings]

9 March 2010

Brother-in-law Jerry came in to be the “contractor” for the den. Put the posts up around the perimeter of the foundation slab, framed it up, made our trusses, and set the window & door frames to have screen insets to keep out the unwelcome flies, yellow jackets, and mosquitoes.

The most difficult fitting was for the chimney stack, but like my other brother in law (the mason) noted it’s like putting socks on a chicken -- you do what's needed to make it work.

[SableSprings]

The frame and temporary oven cover is starting to look like a homeless shelter . I even had some half sheet pans positioned to the sides of the chimney before I figured out how to flash it with the rest of the metal roofing. (Fourth picture shows how I put up some roof edge flashing into the chimney brick mortar to provide a good drip zone around the chimney.) I was pretty concerned that a freak wind would take off the shaky structure, so that’s where the nylon rope and cement blocks came in. Problem was that the metal roof and the big swings in day/night temperatures in our winter caused a LOT of condensation and consequent dripping onto oven. I mean it all got sopping wet within a week...never saw that coming!

Ripped the metal off and put down a plywood roof, some Tyvek house wrap on top of that, and then replaced the metal roofing sheets. We had some pretty nice weather and the perlcrete seemed to dry out pretty quickly. Put some pink fiberglass insulation between the roof and the dome mostly because I had it laying around and then tacked up some plywood sides for further protection. Counted on that to get me through the remaining wet months.

I kept firing the oven at least once a week when we were home until the more permanent den structure was built. Any residual moisture in the perlcrete dried out pretty well with the improved cover and somewhat consistent firings.

[SableSprings]

As winter and the rains approached, I started covering the dome with a tarp and put a cap on the flue pipe. We were leaving for a while so I took the chimney cap off and placed a canopy over the whole structure. Big windstorm took the canopy off and over the fence even though the legs were weighed down with cement blocks. At that point, I decided I needed to construct a temporary, but more stable cover for the oven until I could build the larger den enclosure. Built the faux chimney up a few more levels with hollow bricks to make sure the flue pipe would not get knocked about in the wind.

Used a piece of angle iron and some mortar fill across the back side to provide a level area over the curved insulation for the first course of bricks there. I left some air gaps in the angle iron's support mortar, so any moisture remaining in the dome or insulation would be able to escape up the faux chimney space. Although it doesn't show here, there is a 12" flue pipe that has the working 8" flue nested inside...shows in a later picture I'll post. Once the faux chimney extended above the intended "temporary" roof line, I started creating the frame for the temp. structure.

[SableSprings]

30 October 2009

Picked up three more bags (4 cu ft/bag) of perlite and two 94# bags of Portland cement to finish the dome insulation. Talked to a local metal shop guy about making a stainless steel fire door. Preliminary design called for a "thin box" with handles that would double as stands and a 2" box chamber to contain insulation material. He said he’d create a removable cap for it so I could fill/refill it with perlite for insulation.

Finished the insulation cap on the dome. I estimate between 4"-5" on the sides and probably a little thicker on top. Picked up my fire door and was really happy with what he’d created. Door is rather heavy (about 18# when filled with perlite), but the handles he designed and welded on make it really stable. Cap is held in place with stainless steel hex screws and the door fits perfectly flush against the oven’s reveal. The two pictures below show the door standing on some brick pieces--as I was seeing if air flow underneath was better than just around the sides (when the door was sitting on the landing a few inches from the reveal--see note below).

Continued with some higher end curing fires to finish drying the outer perlcrete cladding insulation. Had the first pizza on November 19, 2009 – five months from the foundation ground breaking. Even Hamelman’s pre-ferment (2-day process) pizza dough could not make that first pizza of ours look good......however, I’ll always remember how good it tasted and the satisfaction of knowing my oven was a success.

Note: I now just stand the door 2"--3" away from the reveal when I light the fire the night before my baking day. Only coals left in the morning and generally the dome has cleared and needs to equalize and cool down to under 600F for my bread baking. I generally bake my breads now around 2:30 in the afternoon and at about 575F in the chamber.

[SableSprings]

You're absolutely correct David...it was a lot of work and didn't gain me anything in the long run. At the time, with my limited experience I thought I would be able to get the perlcrete to hold better on the vertical sides with the mesh firmly in place. It didn't work very well and that's why I went with the outer plywood--to create a consistent width of insulation on the sides and to keep the wet perlcrete from sloughing off while it cured. I thought the mesh being embedded in perlcrete several inches away from the oven wouldn't be a conductor or a problem for the oven. On hindsight, I definitely would have skipped the mesh.

At the time I was starting the outer insulation cladding, I had decided not to stucco the outside. I was going to be building a permanent structure over the oven to protect it from the elements, and I fancied the look of the half barrel brick exterior. Since I had built the "sorta dome" for the advantages it would provide for my baking options, my intent was to create a brick "barrel" facade on the outside of the oven to give me a particular (and different) look to the oven. Addition of the plywood forms to contain the perlcrete while it cured on the sides would create a nice clean vertical wall that, hopefully would be beneficial to laying the facade bricks. I'll try to be showing what & how I got the barrel look with the dome functionality as I continue to document my build.

Incidentally as of last Friday's bake, we've put 4,100 pounds of dough (counting pizza, buns, bread sticks, biscotti, cookies, flatbreads, and regular bread loaves) through the oven since the fall of 2009. That dough total includes the 2,746 loaves of bread that I've made...1,877 (68.4%) given to mostly to friends, neighbors, and local police & fire departments. It's been a terrific, relatively inexpensive retirement hobby...and yes, I keep track of everything on Excel spreadsheets! (What can I say, I'm a retired CIS instructor...)

[david s]

Tried to put a thin layer of clay on the outer dome to smooth it out...waste of time for me. Decided to use 10:1 perlcrete for my top insulation. Made a quick form around the insulation base, leaving a couple of inches gap. Put some heavy wire mesh in place around the dome base form and placed a piece of ˝" leaning rebar to provide additional lateral support/strength for the front arches. Used two bags of standard redi-mix concrete to set the wire and rebar into place. Once the concrete had set, I bent and cut the wire mesh up and over the dome.

I planned for the wire mesh to be in the outer third of the dome’s perlcrete insulation layer. I spread a layer of diatomaceous earth (D.E.) over the dome and planned to spread some of it between each layer of the perlcrete (and the firebrick) as I mixed and applied it. My understanding was that the D.E. would give the firebrick dome some slip from the outer insulation dome...hopefully reducing or eliminating major cracking. I then simply braced pieces of plywood vertical to the outer surfaces of the lower base form. Used up one 94# bag of redi-mix and two big bags of perlite mixing 5 wheelbarrows full of the perlcrete insulation. I ran out of perlite before I was able to close the top.

We had to leave for a month, so I covered the open area of the dome with a tarp and put a canopy over it (double protection from Oregon rains). Ordered three more big bags of perlite hopefully to arrive by the time we returned.

I doubt whether having steel mesh in a weak 10:1 vermicrete mix achieves much. It is also a lot of extra work to get it to conform to a spherical surface. The vermicrete only needs to be firm enough to act as a substrate to apply the outer render/stucco coat onto. Having steel in that layer also increases the conductivity reducing the insulating capacity in that layer. I don't think it is a problem, just a waste of exta labour. Could be wrong, have been before.

[SableSprings]

Tried to put a thin layer of clay on the outer dome to smooth it out...waste of time for me. Decided to use 10:1 perlcrete for my top insulation. Made a quick form around the insulation base, leaving a couple of inches gap. Put some heavy wire mesh in place around the dome base form and placed a piece of ˝" leaning rebar to provide additional lateral support/strength for the front arches. Used two bags of standard redi-mix concrete to set the wire and rebar into place. Once the concrete had set, I bent and cut the wire mesh up and over the dome.

I planned for the wire mesh to be in the outer third of the dome's perlcrete insulation layer. I spread a layer of diatomaceous earth (D.E.) over the dome and planned to spread some of it between each layer of the perlcrete (and the firebrick) as I mixed and applied it. My understanding was that the D.E. would give the firebrick dome some slip from the outer insulation dome...hopefully reducing or eliminating major cracking. I then simply braced pieces of plywood vertical to the outer surfaces of the lower base form. Used up one 94# bag of redi-mix and two big bags of perlite mixing 5 wheelbarrows full of the perlcrete insulation. I ran out of perlite before I was able to close the top.

We had to leave for a month, so I covered the open area of the dome with a tarp and put a canopy over it (double protection from Oregon rains). Ordered three more big bags of perlite hopefully to arrive by the time we returned.

[SableSprings]

1 September 2009

Final oven specs - Oven opening is 19" wide and 11.75" high. Internal dome reaches 20" high at the peak so the oven's door height to dome height ratio is a little low at just under 59% (instead of the target 63%). The widest point inside the oven is 39" and from the cooking door brick to the back wall is 42". It's 11" of landing from the inner door line to the ash slot. The ash slot is 22" wide by 3.5" with another 12" of landing in front of the ash slot provided by the bullnose bricks.

We decided the first curing fire warranted a party. Twelve of our friends were able to come down for an impromptu toast to the first fire in the oven. One of our friends brought some white lightning to start the brief newspaper fire and to share with the gathered guest glasses. Fed the fire twisted sections of newspaper slowly for about 15 minutes to see if my low door height to dome height ratio would draw and breath properly. No problems with the draw once I took off the chimney cap. Put another section of flue pipe on top to improve the draw (and primarily to expel the smoke slightly above the crowd).

Home made whole wheat bread crisped with olive oil and salt & pepper, chunks of Parmesan cheese and some Peppadew (sweet peppers) for snacking while the fire burned. Brownies for dessert after the "fire ceremony".

Over the next week or so, it will probably just be me and my Black Butte Porter tending the curing fires.

[SableSprings]

To fill the gap between arches, I simply cut a notch from each end of a firebrick and set it into the gap. The long end of the firebricks wedged firmly into place so I only needed to use a small amount of mortar to seal the opening–keeping smoke & creosote out. Based on a flue design I’d seen on the forum, I cut two 8" flue pipes at an angle and then mortared them together. This creates a wider collection area that reduces down to the original opening size of the flue pipe. The bond is obviously weak, so I kept a string wrapped around it until it was supported by the outer chimney structure.

Once the 8" cut & joined trapezoid flue tile was set in place over the arch top center, I filled in the gap between arches with the notched firebricks. I continued to build up the front brick work so it tied in both side support (buttresses) columns and created a nice looking entry area. Since we were still in fire season, I put a chimney cap with cinder screen on top of the flue pipe and decided it was time to start the curing fire process.

[SableSprings]

In order to bring the outer landing (beyond the ash slot) up to hearth level, I used regular mortar to set in some 4"x8"x16" cement blocks as a foundation and lift/level. (With the added blocks it was easier to get inside the oven and check for any more big mortar gaps or gobs. Everything looked good enough, so back to work on the landing and chimney arch.)

On top of these cement blocks, I set bullnose bricks as the landing forward of the ash slot and across the entire front of the oven. In the second picture below you can see several of the bullnose bricks just resting on the base blocks. Picked up a two pieces of 2"x3"x3/16" angle iron for the front & back support (and leveling) of the cut chimney flue pipe section. Also set some bricks in place for the front arch side supports so I could experiment to see how everything was going to fit together. I knew that I wanted my chimney to have bricks on the outside (for looks) and my front arch was going to need some serious side bracing to accommodate the resulting downward & outward thrust/weight forces. The front side column bricks had holes in them (standard hollow bricks) and I put some pieces of rebar along with mortar through the stacks to make them pretty damn solid.

I used my curved piece of scrap wood and cut & mortared into place a back and front arch that would support the double flue tile inner cores and the outer brick surface. The gap between the arches was set at about 2" less than the length of my firebricks and enough so that an 8" flue tile would rest evenly between arches. The tops of the two arches were set parallel to each other, again so that my first flue tile would be level for the chimney base.

[SableSprings]

Although I was confident the dome would not collapse when I pulled out the brick/plywood/sand supports & dome form, I went slowly and kept my head out from underneath the dome . The bagging of sand in the platform really helped clearing the oven cavity in a short amount of time. The smooth curve of the short beavertail toward the front also helped in the sweeping out of the loose sand. I was amazed how humid it was inside the dome. Even though there was a fair amount of mortar visible on the inside surface it was, by and large, quite smooth and I didn’t see any reason to try to remove it. There were a couple larger knobs of mortar that descended below the dome surface (just before I put a layer of plastic between the sand and bricks), but they were easily knocked off with a trowel. I found one gap between bricks in about the seventh course that bothered me enough to fix with a pointing tool and ‘Sairset.

Because of the extreme humidity in the cleared dome, I planned to let the chamber air dry in our hot summer weather while I worked on the landing and chimney.

[SableSprings]

I found out that when I put bricks in place to determine how they needed to be cut, I was disturbing the smooth sand form way too much. It also bothered me that the mortar might pick up sand as I laid each chain in place, so I covered the sand form with plastic to keep the sand out of the mortar. (Yes, for those of you that noted the plastic bag logo, we’ve been to the SPAM museum...)

Cut, numbered, and mortared in place, the bricks of the 9th chain are almost vertical. The neck of the teardrop has been relatively easy here since I could use nearly full length bricks to close up. In an earlier chain at the front over the opening, I actually did use a full brick and although it sticks up above the surrounding bricks, I figured it would just be covered up with perlcrete later. The sand form seemed to be settling so I used small slices of bricks here and there on the 10th chain to keep the bricks even with the previous chain’'s inner surface.

Lots of angles, minor corrections, and grinding to fit the 11th chain in place. The keystone will need to be made in two pieces. A friend dropped over with an angle tool and we figured out a way to cut the two pieces so they'd fit reasonably well. Mortared the keystone pieces and tapped them in place with a rubber mallet.

From bare, top slab to setting the keystone (16 July 2009 to 11 Aug 2009).