42” Corner Build in the Shadow of Mount Nittany

[david s]

It is not available in our country, but another alternative is waterproof calcium silicate board. This is obviously too late for you to consider it, but might be useful to others reading your thread.

[Gulf]

I too like that maximum steps are being taken to protect the underfloor insulation. When viewing this thread from on my iphone a couple of days ago I saw some pics of the weep holes, and scoring, along with some bug screening. This morning, I came back to the thread to get a closer look on my laptop. I was wanting to make sure that the weep holes were bug screened from underneath. In my area, dirt daubers will plug those holes in one season making them useless if they are not screened from below. Now, I don't see the pics of the weep holes from my laptop?

[Giovanni Rossi]

Thanks for the added info David. You all started posting about that newer calcium silicate board during my planning but I hadn't seen anyone use it at that time. I think now it's probably easier to source in the U.S. than Foamglas. Though I didn't do any casting, I appreciate your knowledge on materials and techniques. I'll put a little of that to use when I get to the perlite render for the dome.

Joe, The pics are still there in post #22. I was trying to not flood the Forum with posts but that meant putting a lot of info in at one time. I guess the system will only display a max of 3 pics per post and you have to click on them to see the rest. I'll add them again here in case someone is just quickly scrolling. Thanks for pointing that out. You've probably noticed by now that I pay close attention to your posts. Thanks for documenting so well.

[UtahBeehiver]

The new Thermo 1200 CaSi board is suppose to be water "resistant" and I have seen a perlite board that is water resistant as well, although I am not aware of anyone who has used the perlite board. As far as FoamGlas, originally it was a Dupont product with a plant in the US, I believe all FoamGlas is now manufactured in Europe, hence it is hard to get in the US unless old stock.

[Giovanni Rossi]

Buona Pasqua a tutti!

Didn’t have the oven ready this year but hope to make next year’s Easter bread under the dome!

Planned on 4 x 1” layers of ceramic fiber blanket on the dome. The first layer will rest on the CaSil board. The others will rest on the Foamglas. So, 3” of FOAMGLAS is exposed at this point.

[Giovanni Rossi]

Well, I hope I don’t lose the purists out there. As I stated earlier, like many builders, I have been planning an oven for years. I remembered reading about brick oven kits but when I searched I couldn’t find any in the U.S. Forno Bravo had stopped making them but still offered the plans. That’s how I found this forum. I was amazed at the work being done and documented here.

When I started sourcing the tools and products needed, I discovered some supply chain challenges. Then the pandemic arrived, and things got more complicated. Ironically it was info on the Forum that turned me back to searching for kits. While I felt up to the challenge, the thought of cutting all those bricks really started to turn me off. I found BeanAnimal’s build (Pittsburgh) while searching for guidance on foundation depth in my region. His site topography and soil type were similar to mine. Reading his build cemented my thoughts on ordering a kit from the Fire Brick Company. It is an expensive way to build. You are basically paying for the convenience of not sourcing most of the components, of having the bricks cut and tapered and the flue gallery casted.

The U.S. is their largest market. You can pick up the kit at a distribution node near you or just have it delivered curbside for an additional fee. The delivery guy was quite helpful and with 4 of us we were able to get the 2560 lb crate up that steep section of the driveway from the street to the sidewalk with his pallet jack.

The kit is basically precut bricks, cast flue gallery, a couple forms, CaSil board, ceramic fiber blanket, vent pipe, steel door, proprietary refractory cements, and some misc. items to assist the build. Bags of Perlite were used to top off the pallet as packaging material around some of the fragile components. Total shipping from Melbourne to my house was $470.
Yes, I would do it again. I customized the build and every one of the bricks I had to cut reinforced the decision.

The process for assembling the kit is very similar to many of the recommendations on this forum.
I’ll try to point out the departures from best practices as I’ve identified on the Forum. First, the CaSil board is placed directly on the slab and, while there is a lot of discussion about keeping water out of the insulation, there isn’t any recommendation for weep holes and mosaic tile to eliminate it, just aluminum flashing and silicone caulk where it meets the slab. So, as you’ve seen, I built the kit on a platform of tiles and FOAMGLAS.

[Giovanni Rossi]

This plan adds a layer of castable refractory under the floor bricks to balance the mass of the floor relative to the dome. This requires a heat tolerant barrier to keep the CaSil board dry. The plan called for Al foil. A heavy duty roll of plastic is used as formwork. This was a bit tricky to place. Had to use a large clamp and heat gun to fit the corners at the front. The form screwed into the CaSil. I used this opportunity to level the base as it was about 1/8” off east to west. This layer added about an inch of height.

Honestly, I would have rather had thicker floor brick or 2 layers and skipped the castable. The supplied floor bricks are 12”x12”x2”. Had I been thinking, I could have tried to pick up more of them to do a 2^nd layer.

[david s]

It sounds like a kit from the Melb Firebrick Co. Ben built his first oven from advice from this forum. Other builds have used foil as a moisture barrier, but remember that if water does get in, from nail holes or where the foil overlaps. The calsil acts like a sponge and the foil then works equally well to hold the moisture in.
However, with it sitting on foam glass I’m sure you won’t have any problems.

[Giovanni Rossi]

Agree David, I remember you all discussing trapping moisture like that a number of times of the Forum. As I stated, I wished I had thought earlier to source more floor brick and skip the castable but I was running out of good weather and just pushed through. I'll have a couple questions pertaining to this when I get to the render stage that I'll ask you and others to weigh-in on.

Now, on to the next step:

This step was a little challenging. The kit comes w/ 5 bags of castable refractory. About 3.25 bags are needed for the floor and the remaining for the dome keystone. The directions are clear to add water slowly. It wasn’t my first time mixing concrete or mortar, but it was a first for this stuff. I wish I had mixed half the volume at a time, but it was a hot day and I wanted a single pour so the first half didn’t set. The mix seemed to want to stay dry. I thought I had a pretty good product. I shoveled it into the form and started to work it flat and it became apparent that I had added too much water. Also, I didn’t have enough mix! It seemed to be going off fast with the heat so I quickly mixed up more at a dryer consistency and tried to work it into the first batch. I was still short of filling the form and this is the point when my anxiety peaked and I was ready for an episode of reality TV . Not my finest hour.

I ended up mixing two more small batches and using 4 ½ of the 5 bags and then it dawned on me that not only had I leveled the form work but raised it to get a little more thermal mass in the floor. Who knows why I didn’t recall that before. I didn’t plan to cast the keystone so it didn’t matter if I had used it all.

Glad to be done with this part.

[david s]

Yes, the stuff is tricky to work and goes off fast. In hot weather I always use chilled water as it’s really temperature dependant. Don’t leave bags in the sun for the same reason and don’t mix more than 1/2 a bag at a time.

[Giovanni Rossi]

Next up: Floor brick

This topic has seen a lot of chatter on the Forum about whether to mortar the floor or not. The consensus seems to be to dry lay the bricks on the floor insulation. If the insulation is not even or the bricks are not true, use a thin bed of fine sand/powdered clay mixture to make adjustments. Dry-laying is preferred to make it easier to replace a damaged brick down the road. That said, the long-time members will state that it is very rare for someone to replace a brick.

The kit uses 2” thick 12”x12” floor tiles. They are pre-cut to fit the shape of the dome and entry. The literature states they are fired at a very high temp and have sufficient durability for residential use. I recall reading that this company’s commercial oven kits use a second layer that is dry-laid on top of the first so they can be replaced because of the beating received from high-volume daily use.

I was fine with mortaring the floor. The mortar bed was about 10mm thick. All told I ended up with just under 4” of refractory mass in the floor. The kit supplies another proprietary mortar and the builder adds locally sourced sand, general purpose cement and hydrated lime.

I drew a center line from front to back then started with the half tile in the middle to set the alignment and finished height. Letting that one set overnight gave me an anchor to work from the next day. I set the rest 3-4 at a time over a few days so I always had a solid section to tap against to get the joints tight and to preserve level.

The diameter of the floor of the dome is 2” smaller than the CaSil board / castable because the plan calls for the first layer of 1” ceramic fiber blanket to rest on the casted heat bank.

[david s]

You are correct re floor bricks and replacement of bricks. A thicker floor for an oven used occasionally rather than daily means a longer heat up time and higher fuel consumption though. The larger the brick in area the greater the tendency for it to crack because of uneven thermal expansion. With the dome sitting on the floor bricks replacement of those sitting under the dome is pretty much impossible, but because cracking or spalling of floor bricks occurs in the centre, you won’t have a problem with those bricks at the perimeter. Likewise with only occasional use you won’t have a problem with the bricks in the centre either.

You should follow the instructions provided by the kit manufacturer to avoid any warranty issues.The advice provided on this forum is for home builders rather than assembly of manufactured kits.

[Giovanni Rossi]

Planning the dome and arches:

I left the heat bank form work in place to protect the CaSil board from abrasion during the floor and dome construction. Likewise, the heavy-duty Al foil to protect the FOAMGLAS.
The first order of business was to dry fit the first course and get an understanding of the scheme. The 2 arch forms supplied are pictured.

Another debated point on the Forum is whether to build the dome on or around the floor bricks. The consensus seems to be that it really doesn’t matter but there are considerations.

Building the dome on the floor allows for less accurate cuts to the floor bricks. The builder just needs to make sure the dome is supported and that there is adequate allowance for insulation around the floor given the space afforded by the support slab. The downside is, as david s stated in his last comment, the difficulty in replacing a floor brick that’s under the dome bricks. However, those floor bricks would generally receive less wear and tear.

Building the dome around the floor requires more precise cutting of the floor bricks. It is recommended the floor bricks be cut such that a small space at the perimeter is retained to allow expansion of the floor without putting lateral pressure on the dome.

This kit is built with the dome sitting on the floor tiles.

[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!

[MarkJerling]

Looking good Giovanni!