42” Corner Build in the Shadow of Mount Nittany

[Giovanni Rossi]

I was worried about all the water still in the build and the hard freezes on the horizon. Once the flue gallery was in place, I had been keeping two large incandescent bulbs in the oven overnight with the door fit as tight as possible. Not sure how much it helped, but the outside of the dome was warm to the touch each morning.

Once I finished the coat of mortar on the dome, I wanted to try to dry it out a little more. Heeding all the warnings about not firing an uninsulated dome, I loosely wrapped it with two layers of some of the ceramic fiber blanket. Not sure if this was necessary because I wasn't planning high temps; but, just in case...

Then, over 4 days, I built increasingly larger fires with charcoal briquettes and twigs. I didn’t want to push things too far so I stopped on day 4 with the top of the dome at 275^oF, hoping I had done enough.

[Giovanni Rossi]

Sorry for all the posts. Rainy day so I'm trying to get caught up to the present.

I had leftover 2-part mortar so I saved some in plastic containers in case I need to make repairs down the road. I mixed the rest and coated the dome to even the surface and add a little more refractory mass.

[Giovanni Rossi]

Setting the pre-cast flue gallery was a little more challenging. david s frequently reminds us to not underestimate the weight of castings, especially if you need to move them.

The directions recommend 2 bodies for this job. I could carry it by myself but I couldn’t rustle up help this day to mortar it in place. I didn’t trust myself to not let the gallery crash into the arches.

After a little head scratching, I redeployed a bottle jack and cut a section of 2x4 that fit into the gallery from below. This setup allowed me to rest the gallery above the arches. With the mortar in place, I opened the jack valve and eased the gallery in place.

[Giovanni Rossi]

Next up: the vent arch.
This is a simple part of the build using the supplied form and provided the entryway bricks were laid correctly.

[Giovanni Rossi]

I had saved two of the largest bricks to cut and lay flat for the keystone but they were just short of what I needed. So I had to pick up 2 standard firebrick. I joined them with mortar and let them cure overnight.

Needless to say, it was a little challenging cutting on an angle from a dodecagon with an angle grinder!

Again I was inspired by UtahBeehiver but am lacking in artistic talent so I settled for a simple detail.

I’ve read many builds where the placing of the keystone is is both exciting and a great relief. I can second both of those emotions!

[Giovanni Rossi]

At this point the kit plan calls for casting the keystone using the fiberglass dome. I had decided at the beginning to use all brick. The kit has extra to accommodate this.

These were the last six of the smallest bricks in the kit. I wasn’t able to use the trammel at this point bc the bracket that holds the brick was too wide. Had to support each from below as before. I ripped some thin strips of wood and cut them just long enough to be flexed for lateral pressure to hold these bricks in place.

I will cut six of the larger bricks to fit the gaps. When cutting, I soak the bricks for a long time and wear a respirator. I only had my trusty angle grinder for the job so it was slow going as I kept adding water to capture the dust. Definitely would not do a full oven without a wet saw!

[Giovanni Rossi]

The trammel is used through course #8. A fiberglass dome is supplied to provide support to courses 9-11. It is supported from below by whatever means you like, scissor jack, etc. and is flexible enough to be removed via the oven entry when finished. I wanted to have more control over the inside look of the dome and clean as I went so I continued to use the trammel and support each brick.

The last brick course in the plan is #11. These are some of my favorite pics of the build.

[Giovanni Rossi]

Progress slowed as the dome wall became more vertical. With the arch in place, it was time to set up a platform to make it easier to crawl into the oven to clean the excess mortar from the inside of the dome.
Losing daylight earlier made working by trouble light necessary but it made for more dramatic pics

[Giovanni Rossi]

I’ve been checking for level on each course and making sure the inside bottom corner of each brick is set tight to the course below has kept things true so far. I dry fit each row so I can adjust the bricks to make sure I have proper alignment for the mortar joints and determine any cuts I need to make.

In order to finish course #5 I had to build the internal arch. While I didn’t have to, I marvel at the effort of the builders at this stage to calculate and mark the cuts for these bricks. This, like Indispensable Tool design, is necessary Forum reading. The precision of some of the craftsmen in preserving the internal face of the dome is amazing!

[david s]

Just scatter some dry sand on the floor. This prevents any mortar falling onto it from sticking.

[Giovanni Rossi]

The first sign of trouble:

Things were going well until course #5. I had laid the anchor brick for course 5 the night before. When doing an anchor brick I just set it in place and leave it in the trammel over night. This day I finished course #4 and had some left over mortar so I placed 3 bricks next to the course 5 anchor brick leaving the last brick in the trammel.

The next day I found the middle 2 bricks had slipped about ¼ “. I was irritated and confused because I didn’t think the slope was that great at that point and the mortar seems to firm up pretty quickly. It really wasn’t a big deal structurally but it was going to be visible from the entry way.

Now, do I leave well enough alone or risk damaging the dome by removing them? I really should have thought it through before I went at it with a brick set and hammer. The WFO gods were kind to me bc I was successful removing them without any apparent damage to the lower course or the anchor brick. We’ll see once I fire it to working temps. Again, I didn’t think the slope was that great. If you’ve followed this build from the beginning, you may recall that my foundation footing is sitting on bedrock. My site is about 300 ft from a 4-lane road…vibration from the traffic?

What this meant was that I had to support every brick from this point to the keystone. A reminder to new builders to cover your floor because cleaning at the end of the day is impossible with the props in place.

[Giovanni Rossi]

Continuing the build:

Another point to consider is providing a thermal break between the dome and the outer arch. Some builders extend this break through the floor. The reason for this is to reduce cracking from uneven thermal expansion and to decrease heat loss from the dome. Different materials and inventive techniques have been used. If this is of interest to you, it is worth spending some time searching the Forum. A thermal break was of great interest to me because my main reason for building the oven is to bake bread so retaining heat is important. Unfortunately, this kit doesn't use a thermal break and I didn’t think it was advisable to try to cut one in. This is the biggest tradeoff I had to make when deciding whether to use the kit. To try to compensate I’ve increased both the under floor and dome insulation.

You can read a lot about a refractory mortar mix on this Forum. The experienced builders here have perfected this “Homebrew” formula for strength and workablity at an economical price.

The kit I’m using contained a 2-part mortar mix. I mixed it in small quantities at first so as not to waste it and to determine how many bricks I could lay at a time before it went off. At the end of each day I made containers of the combined dry mix in batches enough for 5 bricks. That set me up for work the following day. I typically had a little left over to pack into any gaps on the outer surface of the dome.

The kit has 3 main types of bricks. About 48% are tapered on 1 plane. 44% are tapered on 2 planes and are in 2 diff sizes. The remainder are termed “stagger” bricks and are also in two sizes and are used to help stagger the joints from course to course. The plan shows how to use these on each course but I felt I had to deviate now and again to adjust the spacing. The directions also state to use mortar to fill in small gaps at the front of the dome that would be out of sight. I didn’t want to do this so I had to cut some of the extra bricks supplied. The scheme builds the entry and dome in unison up to the arches.

I have to pause here and say how much I admire those of you who have cut every brick. At this point in my build I had so much work in on my site and the stand that I don’t believe I had the energy or time to do so.

[david s]

With the full weight of the dome resting on the outer floor bricks, I can’t imagine ther’d be much slippage. You should follow the manufacturer’s instructions.

[MarkJerling]

Looking good Giovanni!

[Giovanni Rossi]

Starting the dome:

The next debated decision point is whether to mortar the first course of dome bricks to the floor. I’m not sure from my Forum research that there is consensus. There is a good argument for not mortaring to allow movement as the dome and floor will expand at different rates. MarkJerling did some calculations a couple years ago trying to assess the expansion of different points in a 42” dome. His conclusion was it may be best to let the dome free of the floor. Others argue that any cracks that develop at that juncture would not be seen anyway. I think if I were building from scratch, I would not mortar the dome to the floor.

However, this kit plan instructs mortaring. All the bricks are pre-cut. The process starts with the first internal arch bricks which are laid using height indicators on the forms. With those two bricks set and cured overnight, I had good reference points and anchors for the first course of the dome.

A trammel tool is supplied with the kit. The center floor tile has a hole that receives an anchor pin in the base of the trammel. This tool helps set each brick at the correct angle and distance from center to achieve a proper dome shape. This set up is a little different from recommendations on the Forum to make your, what’s generally termed an “indispensable tool” (IT), such that the pivot point is at finished floor height to get close to a true sphere. It’s worth searching for these terms bc there are many ways to build one of these and you will find some truly creative versions. The tool incorporates a bracket or clamp to properly position each brick. From my reading, the most critical aspect is that an envisioned line drawn from the pivot point through the tool should intersect the midpoint of the brick thickness. It's time well spent doing research on this!

Note: I embraced the direction of UtahBeehiver to place a single brick of the next course at the end of the day to have a solid anchor to work from at the next session!