BeanAnimal's 42" build - Pittsburgh PA

[BeanAnimal]

Okay 15 years of planning and an annual fight or two with the warden regarding "no new projects until the other projects are complete" has finally granted me a permit. I would like to think that my finely honed Jedi Mind trick worked, but alas, I fear she has agreed simply out of frustration and fatigue due to the daily badgering during Covid Lockdown. Actually, does relentless badgering count as Jedi powers?

Anyway - on the to the project.

15 years of planning and when it came time to pull the trigger on materials - I second guessed myself and began redesign yet again!

1. I was afraid of supply chain issues and materials availability
2. 15 years of DIY has caused me to become less fond of the rabbit hole syndrome that seems to plague most projects.The very thing I used to love (digging into the minutia of detail and planning) has given way to just wanting to get things done. Part of that is fear of the warden's wrath - but to her credit, I don't finish a lot of things.
3. I still want to build my oven - precast was likely a better choice, but not AT ALL what has kept this idea alive for 15 years.

With the above criteria in mind, I set out to refine my plans and start sourcing materials. The new goal was to get this done right AND efficiently. The self gratification of cutting each brick is not something I desire any longer - I have spent the last 15 years cutting brick, tile and everything else under the sun. I called the wonderful folks at Forno Bravo about pre-cut brick availability and found out that the they no longer offer the product. Local brick yards are pretty much closed down and supply chain problems are clearly going to be an issue.

I did a bit more research and found an Australian based company that actually exports kits to the USA. Looking at the plans and the design, there is very little difference between their D105 and the 42" DIY Pompeii oven. I fired off an email asking for a bit more details, and the owner of the company called me back that evening. I have to say, I was impressed with the service and the conversation.

So with that said - If there are interested parties, I will document my plans and progress here. I am a bit hesitant, as I don't want to offend our hosts or be seen as promoting or shilling a non Forno Bravo product. I see a few other posts regarding the kit I am building, but they are mostly (all?) Australian builds.

Well that is the background - next post will be foundation/site issues and the plan/solution to those issues.

-Bean

[BeanAnimal]

Given the forum reset - I am going to edit/repost in condensed format.

My property is on a fairly decent size hill in Pittsburgh. I

• 6-10" of topsoil covering orange and grey clay of unknown depth.
• oven will be in a fairly poorly drained (flatter) area of the yard.
• Our frost depth is listed at 36"

Slab on grade: not a good option, as I can't excavate deep enough for a sub base AND get drainage. Any hole deeper than about 8" below grade becomes a clay lined pond!

Final design:

• 36" deep (40+ on high side) foundation
• 10" footing with rebar (calcs below)
• Block walls with all cells filled with grout/concrete (freeze thaw explained below)
• no ground slab (no need)
• stand formed and poured on foundation

Back of napkin engineering...
2,800 Pounds Oven
2,500 Pounds Hearth Slab
2,600 Pounds concrete stand
3,500 Pounds foundation walls
4,000 Pounds footing
1,000 Pounds Finish material (veneer stone)
0,001 Pizza
__________________________________
~16,401 Pounds - wow!

Clay soil bearing capacity - IBC and other codes list 1,500 PSF (likely extremely low estimate)

16,400 / 1,500 = ~11 square feet of bearing surface min

Poured footing

• avg 16" width
• 10" depth
• ~32 square feet
• 44 #80 bags of concrete
• #4 rebar (3 per side on 3" chairs)

So even I up the total live/dead weight of the finished oven to 20,000 Pounds:
20,000 / 30 = 625 psf - a very comfortable safety margin for both the bearing capacity and the footing itself.

[BeanAnimal]

On to the work:

Saturday 5/16/2020 and Sunday 5/17/2020

Manual site excavation: I contemplated renting a small excavator. I hindsight, i should have!

It took most of Saturday and most of the day Sunday to dig the foundation trench.
I used a small 2 bag mixer to mix the 44 #80 bags and dump them into the hole.

I built a small concrete chute and set the mixer directly above it. This was a huge time saver, though climbing in and out of the hole, spreading and mixing got a but tiresome.

[BeanAnimal]

The footing was hand screeded with a board and a level as I worked my way out of the hole (toward the chute side). I am pleased that I ended up almost dead level, with a single 1/2" corner and a bit of a dip (1/2") in the middle of the right side wall.

I will have to trim 1/2" off of the just the corner of one of the blocks when I lay them.

Rain delays, tired hands and a busy daily work schedule have pushed foundation block work off until late afternoon Thursday May 22nd.


Time to address some of the items from post #1

1. Cell grouting: Because this is a "hole" in the ground in clay soil, it really has no natural drainage and the cells will fill with water. Repeated freeze/thaw cycles with that much water will destroy the underground block. Grouting the cells will hopefully eliminate this problem.
   
   The alternative was to form and pour. That meant another 30+ bag continuous pour. No Thanks! I will still have to mix and pour, but can do it at my own pace.
   .
2. The foundation will support the stand directly, a ground slab is not needed, as the foundation bears on the footing. I may pour a floating slab or use a plank floor or pavers for the wood storage area. Will deal with this later.

[BeanAnimal]

Friday May 22, 2020

CMU Block Foundation Walls:
8x8x16

Method: mortar between layers, but not between adjacent blocks. This allows me to tweak level/plumb and keep the perimeter dimensions as small as possible.

10 cells in length by 9 cells in width, no mortar gives me almost perfect dimensions for the foundation, including a ~2" brick ledge WITHOUT cutting ANY block. This also means turning the pattern 180 degrees for each layer gives me the staggered bond that is needed to keep cells lined up for grouting. See the pattern below, noting the corners. Not only can I turn it 180 degrees, but I don't end up with the oddball dimensions changes, as each side has 1 long and 1 short corner. Everything stays symmetrical without the mortar joints being needed to make up the difference.





2 more layers to go:

Not sure if I am going to trim the final layer height or not - I am still working out where the finished ground profile will be and would like the brick ledge slightly below grade. I also don't see a need for a bond beam - but may pour 1 anyway.

There is a several in drop between the back and front of the oven - as well as the front of the oven is going to be adjacent to a walkway and patio. I am not sure how this is all going to tie in yet. Stay tuned!

[BeanAnimal]

Sat-Sun May 23-24

Finished up foundation!

Poured cores and backfilled - rebar added to every other core.

Everything is nice and level around the perimeter

You can see the beginning of the forms for the poured stand walls..

[BeanAnimal]

Week of May 25th during evening:

Constructed the rest of the formwork for the stand walls and integrated opening arch.

Form Notes:

• Exterior walls have 2x6 walers integrated into the framework - this should prevent outward bowing - may add stakes and braces to be safe.
• Exterior wall top and bottom plates interlock - will drill 1/2" hols and drop rebar pins into the corners to secure them during pour.
• Interior walls are somewhat modular - single panels would be impossible to strip, as they would end up wedged in place. Side walls are 2 or 3 pieces. End wall is a single piece but 1/2" short on either side (see photo) so it should slip out fairly easily.
• Front wall/arch form (next post)

All formwork was painted with commercial form release. Cherry smelling mmmmm


Example of modular side wall (not lined up yet)
Left room for top 2x4 plate to tie all sections together in a straight line.



You can see the basic form starting to shape up with rebar going in as well.

Verticals are #4 embedded in foundation cores
Horizontals are #3 bent at 90 on two sides to form sidewall reinforcing that goes around both corners and is tied in the back with significant overlap.



Bends were made using two 3/4" iron pipes for the short 90 and then DIY wooden jig (old crate pallet in photo) and single 3/4" pipe for the long side (you can't slide the pipe off the after a second bend). The wooden jig bends are clearly not as tight - but well within the radius needed to fit in the form corners.


Some temporary blocking on all sides to set wall thickness


Rear wall to the left - notice is is 1/2" short.
Should make it easier to strip the day after the pour, as the side wall forms will come out first.
I should have made the rear wall in two pieces - but was too lazy to rebuild it once I realized that was a better plan!

Detail of side wall panels (3 sections on one side) for easy removal when stripping.

[BeanAnimal]

Coming together nicely



Front span (where arch will be) is dead nuts side to side. Nice!

[BeanAnimal]

And lastly - the slab support arch -

I want to be able to strip the forms within 24 hours - but would like the arch form to stay in place for 10-14 days. It will be in place for the slab pour.

The solution was simple - build the support form and sandwich it between the inner and out form walls. The walls can be removed, leaving the arch form.


Just a simple plywood form covered with coated hardboard - who knew - the big box stores no longer sell regular old masonite - just this coated paper crab that resembles what masonite used to be.



Glued and tacked with a brad nailer - 5" thick and very solid already.



Add vertical sides and bracing form scrap - the bracing will be screwed into from the outside and inside form walls. This sandwich will be very secure and should not spread during the pour.

[BeanAnimal]

Sandwiched in place - almost ready to pour!

[UtahBeehiver]

That is some serious form work. This is going to be a bomb shelter.

[BeanAnimal]

That is some serious form work. This is going to be a bomb shelter.

yep!

Always amazed at how even the most substantial forms bow, swell or outright fail under the weight of a wet pour. I didn’t want canoe shaped walls!

The corner pins worked perfectly. Even with the 2x6 walers, the bottom cord started to bow slightly as I rodded the mix. Given that the walls are 4”, even a bug holed dry pack will be overkill, so I barely rodded and hammered the walls.

6” block walls would have been far easier, but there is a chance that this stand does not get covered, Exposed block is ugly and I don’t care for stucco.

I now have a 2” brick ledge around the perimeter, giving me plenty of option when (if) we decide to veneer.


But yes... a bomb shelter.

[BeanAnimal]

The pour went well. 33.3 bags- exactly what the volume was calculated as in Fusion 360.

A few notes on hand mixing this concrete. Over the past 15 years I have hand mixed ~500 bags of concrete for various projects. In most cases. The pours were non critical things like post holes or simple footers and I have always mixed by eye with the garden hose.

I used this and the footer as a trial run for the upper slab, as that is a critical pour that I want to go well. I measured the water exactly for each batch in the mixer and have to say that I am not at all pleased with then bag to bag consistency of the Sakrete 80 product. Some batches were almost soupy and others so draw that they needed substantial water additions of up to a quart or more. I also. Priced that some batches had a higher sand continent and other far more portland. That is some batches were grainy and others more plastic like. In the end, most batches had to be watered by eye... Also - would have been far better off with two / three wheel barrows and help. First to last bag was 2.75 hours and could have been cut down to 1 hour or 30 mins with two mixers.

As much as I hate to pay for it, I may call the meter truck for the slab. $265 for the first yard... not really that bad considering the saved work and lessening chances of shrinkage cracks due to time between batches.


Arch form left in place. Some bug holes and a few poorly consolidated spots at the base. Not bad at all.


Another shot. Rather pleased with the outcome considering the minimal rodding and side hammering.

The forms literally self separated as the pins were removed. The release agent worked far better than DIY solutions (Pam, WD40,etc) that I have tried in the past. Did i mention cherry scented.... mmmmmmm.

[GreenViews]

Greatings BeanAnimal! I'm Tom (Greenviews) from Indiana. We're relatively close and starting at about same time. I just made my first build post showing base for my table on which I will place my oven. Your base looks prettier, but I have plans to later stucco coat my block base. I'll try to keep an eye on your post. Are you still importing your kit? I foolishly plan to do all my cutting . Cheers

[BeanAnimal]

Greatings BeanAnimal! I'm Tom (Greenviews) from Indiana. We're relatively close and starting at about same time. I just made my first build post showing base for my table on which I will place my oven. Your base looks prettier, but I have plans to later stucco coat my block base. I'll try to keep an eye on your post. Are you still importing your kit? I foolishly plan to do all my cutting . Cheers

Thanks Tom!

Yes - I went ahead and purchased the kit. I did a lot of research and am very comfortable with my decision.

My rationale was simple:

• 15 years ago, I would have been happy to cut brick. Now - after a fire pit, a stone patio and stone walkway, 2 decks, raised beds, and a whole home remodel - I don't see the reward in cutting brick!
• With a 3,000 pound wooden crate in the driveway - the warden is hard pressed to change her mind. Doddling around trying to source stuff would have given her chance to take back her approval.
• I have to source very little a-la-carte - and am at this point in life happy to pay a premium for that.

I still get to build my oven brick by brick and enjoy the reward - Honestly, if I were to "do it again" - recognizing I am not even close to being done - meaning if we ever move, the next oven will likely be a pre-cast dome - or a contractor can build the foundation and stand

A few notes: The 42" kit has a 6" chimney - I think some here may frown on that - but I see no complaints from other "kit" builders. Also - my chimney height will be taller, as it will have to pass through the timber frame enclosure roof and extend at least 3' feet past. It should have plenty of draw.

I mentioned it in the first post - but I did call Forno Bravo to inquire if their DIY kits were still available - they are not.