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Old 09-14-2009, 11:56 AM
kebwi's Avatar
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Default Yet more foundation discussion

I apologize that some of these questions come up with minor variations over and over, but please realize that for those of us who are complete novices in construction, confidence in the designs and specifications is shaky at best.

The Pompeii directions prescribe a 5.5" #4 rebar and mesh reinforced foundation.

I meticulously calculated the actual pressure that the oven is going to impart on the foundation wall, factoring in the weight of all materials involved and dividing by the footprint of the wall against the foundation, as subtracted by the voids in the empty cores, and I got a whopping 6 lbs / in^2. That's right. The full weight from the bottom of the walls to the top of the chimney should be in the 4000-6000 lb range for a stucco design and the footprint (for my exact wall design) is 996 in^2, and that is with two openings in the wall. Thus, about 6000 / 1000 = 6 lbs / in^2, and that's for 6000 lbs, the heavier end of my weight estimate. Given that the original Pompeii directions have only one opening, there is more area against the ground in such a design and thus even lower overall pressure, maybe as low as 3 lbs / in^2 for a lighter oven on a complete wall.

This makes me wonder why I need 5.5" of #4 rebar and mesh concrete. Please forgive my naivete in these matters. What am I missing here? My favorite contractor (I realize many folks on this forum are weary of contractors because they may not understand the demands of a brick oven, but be that as it may) suggested 4" of meshed concrete, job done.

I'm thinking about the guy who decides to take this thing apart some day, I don't want to make that eventual job more difficult than necessary...but without sacrificing the stability of the oven. I really don't want to sell out the oven's stability, but I don't want to do more than is necessary and make the job down the road a hundred times harder.

How about 4" with mesh? Would I be a naive fool asking for my oven to fall over in a pile of rubble if I went that route?

Thanks.
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Old 09-14-2009, 12:27 PM
Jed Jed is offline
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Default Re: Yet more foundation discussion

Hey Kebwi,

My opinion is that you would be fine with the four inch, wire mesh enforced, slab to support an oven.

What the guys who put the instructions together can't know will include a variety of variables about the guy (person...) doing the building, the materials, and the site. If frost heave was a concern, if the soils are unsuitable to support any weight, the the actual concrete used is weak, etc. With that in mind it is reasonable to develop a basic plan that makes it easier for a novice builder to end up with a safe, and stable oven. Against the engineers math I would expect the standard plan is 'over designed' for most applications, but that just makes for a longer lasting product, at a nominal additional cost.

Good luck with your build.

JED
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Old 09-14-2009, 02:25 PM
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Default Re: Yet more foundation discussion

The cost of the rebar and additional 1 1/2 inches of concrete are negligible in overall cost (and manhours) you are putting into this thing.

It may or may not be over designed, but one thing I have never heard on a construction project is the phrase "Danm, I put too much rebar in that foundation"
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Old 09-14-2009, 02:29 PM
kebwi's Avatar
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Default Re: Yet more foundation discussion

I really didn't mean to give the impression that my consideration was economically motivated. I agree, I don't care about the cost of the extra concrete and rebar at all. I was far more concerned about the difficulty of one day dismantling it.

Basically, I imagine some ornery home-buyer may not want it :-( and if it's easier to rip it out, all the better.
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Old 09-14-2009, 02:36 PM
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Default Re: Yet more foundation discussion

I think a well designed and executed WFO would be a welcomed addition to most any home even if the home-buyer may never use it.
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Old 09-15-2009, 09:09 AM
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Default Re: Yet more foundation discussion

I agree with Neil. Nothing better than doing it right the first time, overkill is always better than underkill. Also, I wouldn't even consider how hard it might be for a future home owner to demolish your oven foundation as a factor in how stable to build your foundation. Tearing up a 5" slab is no more difficult than tearing up a 4" slab. Also... if the day comes that you sell you home and the potential home buyer does not like the pizza oven, tell him NO DEAL. He doesn't deserve to buy your home!
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Old 09-15-2009, 09:12 AM
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Default Re: Yet more foundation discussion

You guys rock. :-D
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Old 09-15-2009, 01:09 PM
Il Pizzaiolo
 
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Default Re: Yet more foundation discussion

Speaking from experience...The poor sap that has to break up and haul away your rebar/mesh enforced slab IS NOT going to be able to tell the difference between a 4" slab and a 5 1/2" slab. Without a jackhammer and a bobcat, enforced concrete slabs are a real B**** to remove.
Have the added piece of mind and go 5 1/2", build it as heavy (stone or brick finish) or as light as you want.....worrying about the removal is crazy, unless you are pretty sure that person will be you...in which case YOU are screwed regardless of the thickness.

RT
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Old 09-15-2009, 08:34 PM
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Default Re: Yet more foundation discussion

I just finished my WFO and for what its worth the peace of mind I have knowing I overdid it on the slab thickness and rebar, the patience I took in laying each chain of bricks and the thickness of the ceramic blanket I used (3 boxes, 4 layers) gives me comfort that I don't worry about the slab shifting, bricks cracking or dome being too hot (I had it up to 800 degrees in the dome last night and the dome was ambient temperature to the outside air). For the next person who buys my house...if they want to tear it down..that's their loss not mine.
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