Another Minneapolis WFO

[MnDude45]

Take it easy, Sixto. That smoke last week was brutal. Keep plugging away!

[RandyJ]

Hey Sixto ,when i did my oven base i doug 12" around the outside of the base and 6" in the center. My soil was very sandy so had good drainage. I haven't seen the oven up close in over 2 years as we sold the house but i saw it from the street today as we biked past and it still looks to have not moved at all. I have been helping a friend build a garage and they did the exact same thing for the slab for that. So i would think you are ok to do something similar to that.

As for the construction are you planning a igloo style? I know a few have had issues in the cold and snow with water getting in and wrecking stuff. You may want to consider some kind of enclosure to help protect the oven from the weather. The biggest issue is that the weight will climb. Mine was i believe close to 16k#. If you have questions send me a message and I would be happy to help .

Randy Janssen

[Sixto]

As for the construction are you planning a igloo style? I know a few have had issues in the cold and snow with water getting in and wrecking stuff. You may want to consider some kind of enclosure to help protect the oven from the weather. The biggest issue is that the weight will climb. Mine was i believe close to 16k#.

Hi Randy, thanks for sharing your experiences! I ended up going down 2' below grade and pouring a 1-foot thick reinforced concrete footing. I laid down landscaping fabric on the undisturbed soil and added a couple of inches of sand/gravel above that to help with drainage immediately below the concrete.. The concrete pad is 5' side to side x 6' front-to back. I figured if there is any movement, the whole thing will more likely move up or down with soil moisture and frost conditions. It ended up being about a cubic yard of concrete, and rather than mixing it myself, I opted to have ready-mix delivered... it took about 15 trips of the wheelbarrow.

So-far there is about 2100 pounds of block, mortar and grout above the foundation... by the time the brick dome/igloo style oven is finished, I'm sure it will be close to your figure which ends up being just under 4 pounds per square inch of net weight over the entire area of the foundation (assuming even distribution)... if my math is right, it's just a little over-designed... :-)

I'm attaching a few photos of my progress... 3 photos per post... I will pause construction over winter and resume in the spring.

Sixto

[Sixto]

My son helped me rake the concrete into place, since there wasn't an easy way to maneuver the wheelbarrow around all sides... I did the shuttling back and forth from the truck to the hole. Our friend Nick offered free advice, and my wife was the photographer from the roof deck...

[Sixto]

I made a form with 2x4's to locate the vertical re-bars and placed (fiberglass reinforcement rods in the holes, had to use a mallet to pound them into the still-wet concrete, to get around a few horizontal bars that were in the way... And started laying block (be easy on my masonry skills, I'm learning as I go....) at least it's fairly level. I'll fill the cores that have rods in them, and seal the open cores with plastic to prevent any issues with ice over the winter...5

I do have one question for those that have used homebrew refractory... I ended up with 3 bags of ready-mix mortar that I'm keeping dry till next year...Assuming it's a 3:1:1 mix, can I add 1 bucket of fire clay for every 5 buckets of ready-mix and end up with a workable refractory? (theoretically that would give me 3:1:1:1 for sand, cement, lime and clay). I have not come across any references to people adding clay to ready-mix grout so far...

[MarkJerling]

Well done Sixto. Looks good!

[mongota]

Free advice from the neighbor? NOTHING is free! Next time, charge him if he wants to give you advice. lol.

Process looks terrific. A great project for you and your son to build now, and enjoy later.

[david s]

"I do have one question for those that have used homebrew refractory... I ended up with 3 bags of ready-mix mortar that I'm keeping dry till next year...Assuming it's a 3:1:1 mix, can I add 1 bucket of fire clay for every 5 buckets of ready-mix and end up with a workable refractory? (theoretically that would give me 3:1:1:1 for sand, cement, lime and clay). I have not come across any references to people adding clay to ready-mix grout so far..."

That would work if you knew the exact proportions by volume, of the ready mix mortar. You are assuming it is in the proportions of 3:1:1 sand, cement, lime. As mortar is usually weaker than that, more like 10:2:1 and who knows what else they throw in, you could end up with a mix that might not perform as it should. If you call the manufacturer they may be able to help.

[Sixto]

That would work if you knew the exact proportions by volume, of the ready mix mortar. You are assuming it is in the proportions of 3:1:1 sand, cement, lime. As mortar is usually weaker than that, more like 10:2:1 and who knows what else they throw in, you could end up with a mix that might not perform as it should. If you call the manufacturer they may be able to help.

Great suggestion, makes sense to confirm the ratio of sand, cement and lime, and adjust them too if necessary. We'll see what I can find-out!

Thanks, Sixto

[Gulf]

Another word of caution. Most bagged mortars do not contain very much hydrated lime for that part of the recipe. The original formulas for masonry cement from which mortar is made has changed over the years here in the U.S. The change has been in the hydrated lime content. Lime was in the original recipe to increase the mortars workability. Since it was highly irritating to human skin the industry has allowed much of the lime content to be replaced with an 'equivalent" amount of crushed limestone and some other proprietary additives. It is still just as good or better for general brick laying but the "equivalent" is not good for our purposes. Crushed limestone does not react the same way as lime when heated. It swells!

There are very few companies that bag the original formula with hydrated lime so be careful. As for as the sand content is concerned here is the mix for the two most common bagged mortar types.

Type-N: 1 part Portland, 1 part lime, 6 parts sand.
Type-S: 2 parts Portland, 1 part lime, 9 parts sand.

[Sixto]

Thank you for the info about crushed or pulverized limestone, Gulf! I confirmed that was the case by looking up the manufacturer's data sheet https://www.midwestmanufacturing.com...SMortarMix.pdf
I will return the remaining bags and get the right basic ingredients in the spring. Sill have a couple of days over 50 degrees forecasted, so I will try to fill the bond beam at the top of the wall with core-fill before putting away the trowel for the winter.

Sixto

Another word of caution. Most bagged mortars do not contain very much hydrated lime for that part of the recipe. The original formulas for masonry cement from which mortar is made has changed over the years here in the U.S. The change has been in the hydrated lime content. Lime was in the original recipe to increase the mortars workability. Since it was highly irritating to human skin the industry has allowed much of the lime content to be replaced with an 'equivalent" amount of crushed limestone and some other proprietary additives. It is still just as good or better for general brick laying but the "equivalent" is not good for our purposes. Crushed limestone does not react the same way as lime when heated. It swells!

There are very few companies that bag the original formula with hydrated lime so be careful. As for as the sand content is concerned here is the mix for the two most common bagged mortar types.

Type-N: 1 part Portland, 1 part lime, 6 parts sand.
Type-S: 2 parts Portland, 1 part lime, 9 parts sand.

[Sixto]

Back at it after a long winter hibernation... I'm the one with the mask, trying not to breathe cement dust.:-) Sixto. It was great to have my pal come over to help, not just for the muscle, but also for the cool italian vibe he brings to the party.

I used fiberglass rebar, to avoid issues from water seeping into cracks and rusting the rebar down the road. I also wove the bars together instead of wiring them, and waited till I had 2" of concrete cover in the forms before placing the grid and continuing to fill the form.

The first photo shows the two wood storage compartments (One faces the back) I wanted to have a wall in the middle to tie the two long walls together, and take up some of the weight of the dome. The front and rear lintels are made from lintel block chamfered at 45d with an 8" diamond blade mounted on a grinder. (needed a spacer to fit right).

I also placed 4 vent holes (about 1" diameter Vinyl tube for stiffness, filled with a length of thick foam backer rod. (in case the vinyl tube doesn't want to come out)

I rented the mixer at 8:00 a.m. and returned it at 3:30 pm (with a lunch break and a quick trip for 6 more bags) Total was 22 bags of 60# ready-mix (3,000 psi) Slab is 4" thick x 6'-2" deep and 4'-7" wide, I did chamfer the back two corners about 9" to get more clearance between the garage and fence.... it's a bit tight walking back there.

I will post photos of the finished slab after it's cured and I've pulled the forms. It's now curing under wet canvas...

[NCMan]

Happy to see you're back at it and looking forward to your build.

[Sixto]

While I'm waiting for the slab to cure I had a few questions:
1). How long do I keep the curing slab covered with a wet blanket? It's been one day so far, and the top surface is already hard to the touch.
2) is there a case to be made for adding a closeable combustion air inlet at the base of the dome, and a corresponding closeable vent at the top of the insulated door? I'm thinking about maintaining temperature by re-stoking firewood overnight on day 2,3 or 4 to keep the oven temperature in a baking or roasting range...
thanks! Sixto.

[david s]

1. Keep it wet for a week. The strength build up is greatest as soon as the reaction begins, then slows down. Most of the potential strength gain has occurred after one week. Concrete strength tests are usually done after 28 days, but a week is considered sufficient. Best to throw some sheet plastic over the wet blanket to seal in the moisture.
2. The air inlet for the oven is provided by the oven mouth. A well designed flue gallery leading to a flue or chimney with an adequate cross sectional area is important.