Pdx 42" update

[Macrinehart]

Today I decided to take the form off. It's been 12 days since I poured the hearth.

I think it looks pretty good. The top is a little rough aftwr removing the loose material and I think it could use some patch work.

Sides are better except around the attempted bulldoze, which was done too late in the curing process. I encountered two issues on the bull note- first the concrete was too hard when I started. I should have just let it be. Second, I had covered the forms with painters tape, and when I used the bulldoze trowel it torn up the tape on the edge of the forms and embedded it into the concrete. If I had a do over I would not use the tape on the top 3/4 inch of the walls.

One you get below the mess with the bull nose things look pretty good! Minor air bubbles, no major holes, and the cove trim around the bottom edge is virtually perfect all the way around!

I suppose I can patch this up with some mortar. The top still feels a little gritty so I'll let that dry and brush it off. Maybe some leveler, or just mortar?

cheers!

[Macrinehart]

The question of depth of oven opening, flue gallery and flue size has had me thinking about the details on this part of the oven. I've read some anecdotes of differential configurations, but not why's. So today I decided to do a little research.

First call was to our local sheet metal fabricator. They don't have directly applicable experience but their opinion was that for forced air systems, which is their specialty, the crossectional area for transitions needs to be consistent. So for an 8" pipe, that 50.27" of area, which suggests an flue gallery opening with the same area. Some options: 4" x 12.6", 5" x 10", or 6" x 8.4". In theory, a reduction in crossection area could result in a negative pressure, pushing smoke back down the chimney and out the front of the oven.

A second design consideration comes from firebox design and cod specifications, where the following ratios are recommended from fire box to flue opening:
Square: 10 x 1
Round: 12 x 1
Rectangle (with aspect ratio > 2:1) : 8:1

So based on a 41" diameter oven, a rectangle flue gallery with 2:1 or better aspect ratio needs 173 sq opening. That looks like a 9" x 19.25" opening to the flue gallery! But of course that needs to shrink to an 8" pipe, which could lead to a negative pressure. Seems like a lot more than I've seen discussed so far.

I'm also thinking that because the actual fire is not going to be using the entire oven floor, maybe the firebox specifications are overkill?

Welcome any comment on this from the pros. Thanks!

[david s]

yes. You'll notice how much extra space you get between the gallery and the dome.
Let these pictures do the explaining.

[Macrinehart]

Hi david s - I drew this crosssection view, is this what you mean by setting the flue gallery inside the oven perimeter?

[david s]

To make the flue gallery shallower it can be set inside the oven perimeter. As the dome rises it gives you more space for the gallery vent opening. Building in brick units reduces the ability to make the gallery thinner and thereby shallower.

[MarkJerling]

.....Actually, as I look at it I realize that I presume on my initial plan that the chimney landing has to be "outside" the door reveal so that the oven can be fully sealed when the door is closed, right?...

100% correct.

....
As I was walking on a beautiful spring day I saw a vision of my future oven clad in a mosaic tile depictions of the park, reservoirs and forest from each of the cardinal directions.

Dang! Sounds like a real work of art. And I was happy when I painted mine the other day!

[Macrinehart]

For visual perspective I arranged a few brick over the floor template to illustrate the outline of the oven opening and chimney landing.


I put the 36" T there to visualize reach with a pizza peal. The plan calls for a decorative arch outside the chimney landing which I planned at 4.5" deep (another half brick beyond this model) but I suppose that is not required to be that deep.



The landing is not to scale, but gives a close idea of my thoughts for eventual placement and size. Actually, as I look at it I realize that I presume on my initial plan that the chimney landing hs to be "outside" the door reveal so that the oven can be fully sealed when the door is closed, right?

In other news, a walk this afternoon inspired me to name this project after or neighborhood Park. The entrance to Mount Tabor Park, which I am told is the only dormant volcano inside the city limits in the US is located about 3 blocks from our house. It's 176 acres and features three beautiful open reservoirs that used to supply city drinking water for Portland, plus old growth forest, and a public concert venue located inside the volvanoe's caldera!

As I was walking on a beautiful spring day I saw a vision of my future oven clad in a mosaic tile depictions of the park, reservoirs and forest from each of the cardinal directions.

https://www.portland.gov/parks/mt-tabor-park

[Macrinehart]

I just wanted to say thanks for all of your posts. I am grabbing information from your build as we work on ours.

Thank you, Miles! Also thank you to Mark Jerling, David s, Gulf, Mongo, UtahBeehiver, NC, and others that have contributed their experience and insight! I really appreciate all the help, and hope to pass what I'm learning forward. This is definately an excellent community!

[Macrinehart]

That's a crazily deep entry you have planned. The deeper the entry the harder it is to work the oven.

david s thanks for this feedback. It reminds me that the floor template was originally drawn without the door stop reveal, and that line I drew on the bricks also is missing the reveal. The depth of the opening is about 22" to the interior of the oven, but after the opening arch the width should be an additional 3" (1.5" reveal on each side).

That said, I am concerned about open depth too. I will dry stack some bricks to play with this some more.

[Doodbird]

Hi Mac,

I just wanted to say thanks for all of your posts. I am grabbing information from your build as we work on ours. I don't think that I will go through the trouble of cutting bricks for the wall parameter on the floor. We haven't decided on diagonal vs herringbone yet. I hope to layout floor bricks in a couple of weeks.

[david s]

The best way to cut curves is to cut straight(s) and then take off the excess. Obviously, binding a grinder blade in a cut is never a good idea. I used diamond blades and that worked very well. Work in a well ventilated space and wear a mask.

And make sure you cut them using a wet brick saw. That's a crazily deep entry you have planned. The deeper the entry the harder it is to work the oven.

[mongota]

When you cut your floor you might already be aware, but you don't have to cut it "as is" as shown in your photo. Meaning, the offcut shown in red can be cut up into smaller pieces to make the infills shown in green. That'll save you from having to cut up those two whole bricks just to get the two green triangular infills. Look through your floor pattern and you'll see how offcuts from one area can be used as the infills in others.

[MarkJerling]

Thanks for these tips, will give the diagonal a try.

UtahBeehiver, your picture raise another question I've been wondering about - cutting rounded edges for the boarder of the floor, as well as the intersections between the interior dome wall and the opening arch?

I've seen videos of folks using an angle grinder to cut these curves, plus a stone chisel and hammer for finishing, but I keep imagining the spinning grinder wheel getting bound in the curved cut and exploding into flying bits of shrapnel.

Is that how people are actually doing those cuts? Any safety protocol aside from the standard precautions (gloves, face shield, mask)?

The best way to cut curves is to cut straight(s) and then take off the excess. Obviously, binding a grinder blade in a cut is never a good idea. I used diamond blades and that worked very well. Work in a well ventilated space and wear a mask.

[Macrinehart]

Did some more playing around today with the advice on diagonal floor, but took a variation and built a V-pattern with the vertex aligned between the oven dome and landing. I also did a more thorough evaluation of bricks using a carpenter's square to check all the bricks from my prior effort.

Couple of thoughts out of this exercise. First, I rejected about half of the bricks due to various quality issues that would be irrelevant for the dome but possibly contribute to problems with the floor. Mostly these rejections were based on angles not being square. I figure minor variations in thickness can be compensated for by using the v-notched sand/fireclay bed under the floor. But that will not necessarily compensate for bricks being out of square, especially with the herringbone pattern.

The second thing is that while I did get tighter lines with my quality bricks, the layout was still not "perfect". I decided that modeling this on the template was not going to guarantee the same results on the real thing. Bottom line, it was a good practice exercise, but every time I do this, even if using identical bricks in the same configuration, it is going to come out a little different. I am glad to hear from MarkJerling that minuscule gaps will fill in with ash. With that in mind, I put away my toys for the weekend.

[MarkJerling]

Hi gang - Here's the latest from Portland! So today we put what is hopefully the last of the freezing weather behind us, although we are in for more rain over the next week. Nevertheless, we had a beautiful sunny morning today so I jumped on the opportunity to check out the hearth and make some progress on the build!

first stop, cleared out the tent and space heater, and then took a peak at my hearth to see how it's doing. It looks like a concrete hearth, no surprise there! The loose sandy material on top is about 1-2 mm thick, not a huge deal in my humble opinion. But I'm giving it another week under the plastic before I remove the forms. (That will be 2 weeks total). Weather will be highs in mid 50s (F) and lows in mid 40s with rain showers for the entire time.

Not satisfied to look at the hearth and will a week to pass in an instant, I decided to pull out the full size floor template, pick through firebrick that arrived last week layout the floor. The next couple shots show the formation of my herringbone pattern, which I realized is quite a puzzle, especially if the pattern starts to get out of alignment. I was expecting the bricks would have some variation in quality. What I didn't expect was for bricks to not be square or plumb. Yet there was some of that so I ended up doing a lot of sorting to build the best floor possible.

I was thinking of building a very large hand sanding disk to go over the floor once it's set in it's final arrangement but I think that could possibly have some unintended side effects, such as expanding gaps for bricks that are not perfectly plumb. Welcome feedback on that idea from the pros!

As for the trial run, I've attached pictures here and am interested to hear if this setup is good enough, or if any of the gaps are unacceptable. Also welcome any tips on how to maintain tight fitting herringbone pattern, as I can see that any small imperfection on one side becomes an unacceptable problem as I continue to layout the floor. Thanks in advance for everyone who's following along and offering tips!

Having done both herringbone and inside the walls, I have to say I like your floor. Is it necessary to go herringbone? Probably not. Does it look good? Absolutely yes. Does it work well, absolutely yes!
Herringbone pattern works well because it limits uncontrolled movement which is why it's used for driveways.

You need not worry about any miniscule gaps as they'll soon fill with ash.