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james 07-04-2005 07:49 AM

Using Existing 4" pad
I was asked if you could install a brick oven on an existing 4" pad that has the fiber additive, but with no rebar or wire, or footing. The site is in the NW, so there are no freeze issues.

My initial thought is that it should be OK, but wanted to run it by the group.


paulages 07-04-2005 11:50 AM

my question would be: how old is the pad, and thus is there any knowing the psi strength of the concrete? if possible i would dig around the edges and check for good compaction beneath the pad.
using the estimated figures in the "how much weight is on the stand" thread, you could guessticalculate (maybe based on a low psi figure) how much the pad could handle.
also, they could broaden the footprint a bit (reducing interior space, but reducing specific pressure on the pad.)

james 07-04-2005 01:56 PM

Thanks Paul. I'll let you know what happens.

paulages 07-04-2005 02:00 PM

by the way,
where are they in the NW? i'd love to hook up with someone else up here who has built or is building one.

sledge 08-01-2005 08:25 PM

If you built the oven on an existing pad, would you still want to pour a thin (maybe 1 1/2" to 2") vermiculite insulating layer? Would you perhaps also need to pour the "isolated hearth"--the regular concrete in the middle of the insulating layer?

I'm curious about this, because my idea is to build an oven "at ground level"--mainly because I'm trying to adapt a project I've already started to include a pompeii style oven in it. I have a six inch footer (8 inchs in the ground--meaning two inches from the top of the footer to the grade) and am thinking about just building the oven on that. Would the heat soak into the footer and ground too much or would the ground and footer be enough insulation already?

Thoughts? I'm wondering if this will even work or not.

Robert Musa 08-02-2005 09:30 AM

i was concerned about the same issue when i built mine. i imagined the patio cracking down the middle and then both sides cantilevering up into a "V" but cracking hasn't been an issue so far and i've got more weight (due to the tandoor and bbq counter) than most. my patio is unreinforced concrete and underlying soil is clay. there was another builder on the old forum who also built on an unreinforced patio with no problems, however, soil compactability might be an issue (e.g. might be a problem if patio was poured over loam for instance).

sledge 08-02-2005 04:50 PM

I'm a bit concerned about my pad as it is reinforced with rebar...I'm a bit concerned about it heating and cracking the concrete...but mostly concerned about the heat retention properties without an insulating layer of concrete...does your oven maintain the heat properly?

Did you put down a layer of the vermiculite or perlite blended concrete over the pad before you built the oven?

Thanks Robert,

Robert Musa 08-02-2005 05:09 PM

sledge, for the pompeii i didn't use the existing pad as a portion of the hearth but rather as a foundation for the stand. if you wanted to use the existing ground level slab as a portion of the hearth then i certainly would create an insulating layer or it will take forever to get the oven hot.

my tandoor is probably more similar to what you are planning. i did totally isolate the brick hearth of the tandoor from the slab with a layer of 3 to 4 inches of cement and vermiculite on the bottom and on the sides (island hearth style), however, i don't have any idea how much heat "bleeds away" with the arrangement because once the tandoor is hot, the food is done pretty quickly (being small chunks on skewers and all) and i've never gone in after the fact with the temp gun to measure how hot the tandoor oven is several hours later.

based on my experience with the vermiculite / cement mixture on the pompeii, 4 inches does one hell of a job of insulating and retaining the heat once you get it up to speed.

if i were you, i think i would also build up the area under the vermiculite area with 1/2 to 1 inch of concrete or grout to keep rain water from entering the vermiculite / cement mixture during the wet season (e.g. don't put the vermiculite / cement mixture at 'sea level'; build a little plateau).

Alan 08-04-2005 09:59 AM

What about floating slabs vs. frostline foundations in freezing areas?

I'm in the northeast (central PA); our max frostline is 30". I don't have room to insulate the ground a great distance around the oven. I'm torn between pouring a reinforced slab over 5-6" of compacted crushed limestone (as is common in floating patios in this area) versus digging a big 3' deep hole and doing the footer and block wall thing. Either way, my oven will be on a block base and well off the ground.

Robert Musa 08-04-2005 10:44 AM

i'm no expert on frost heave but it seems to me that if the "footprint" of the floating patio was only slightly larger than the perimeter of the oven base or if the oven were not in the center of the patio slab, then you would run the risk of ending up with the leaning tower of pizza ... (couldn't resist that one). on the other hand, if the floating patio was significantly larger than the base and the oven was not on the outer edge of the patio then there would be less risk.

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