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uneekwahn 06-24-2012 04:26 AM

Question about ground insulation
I did post this before but for some reason it wasn't approved by the mods :(

I'm looking at building a WFO in my backyard. I have just had a limestone retaining wall built, and as my property is tiered, I have the ability to have the floor of the pizza oven on the highest level, meaning I don't need to build an actual base.

Here are some photos.

In this first photo, the area where the oven will go is (unfortunately) directly behind the post.

In this photo, you can see the area a bit clearer.

And finally, the area where the oven will go. Basically right in the corner.

After today's effort of bitumen sealing the back of the wall, next weekend will be backfilling the area and then having it paved the following week.

There will be a 1.5m2 (about 5'2 - not sure how to symbolise feet squared?) area left of plain, clean sand. This is where I plan to build the oven.

I plan on making a concrete foundation and am wondering whether I need to lay insulation below this? Could I put some form of insulation material into the concrete? Would I even need to worry about insulation?

Look forward to hearing people's thoughts.



Faz 06-24-2012 05:12 AM

Re: Question about ground insulation
You need the insulation between the concrete and the oven.

The oven will be quite heavy - do you know if the retaining wall will tolerate the extra weight? I'd also be concerned about the building the oven directly on such recently made ground, as there is likely to be some settlement. Will you be able to dig footings down to good ground to support the slab?

Lburou 06-24-2012 05:30 AM

Re: Question about ground insulation
Hello Jason, I left this response in your first thread (it made it) and then I found this thread. I agree with Faz, the back of your oven needs the same footing and some kind of blocks to support the back side of your oven, or it will compromise your entire structure. :)


Originally Posted by Lburou (Post 133730)
It looks like you have a good location Jason :)

I don't see any value added to insulating underneath the slab. If you insulate as depicted in the pompeii oven plans, the insulation will be on top of the hearth slab and the oven on top of that.

Looking at your retaining wall, I'm sure the wall will hold the part of the oven resting on it....What I have a question about is the backside of the oven.....? Without a footing and blocks to support the back side of the oven, it will certainly settle and that will compromise the hearth slab for level and who knows what else. Are you planning some kind of support (roughly equal to the wall support) for the back side of the hearth slab?

Best regards, :)

uneekwahn 06-26-2012 05:11 AM

Re: Question about ground insulation
Hi guys, many thanks for the responses.

I hadn't given any thought to laying some form of foundations at the back before laying the slab. The guys laying the pavers will be compacting the area prior to paving, and I was hoping that that would be sufficient enough.

Regarding the limestone wall and whether it would take the additional weight, the oven won't be on the wall directly, but butted up to it.

Here is my dodgy drawing of what it would look like from the side.

My father was once a construction and maintenance manager for a reputable home building company a number of years ago and he believes that compaction of the soil by the brick pavers would be sufficient. He hasn't done this for a long time, and I am definitely happy to take on board what others here are saying due to your experiences.



SCChris 06-26-2012 07:36 AM

Re: Question about ground insulation
I see 2 areas of concern in your drawing and you may have them addressed already.

1. For the effort and cost, I'd want to add some foundation to the pad the oven will sit on. It could be as simple as increasing the pad thickness or a more formal footing. Ideally the foundation is a single structure and this will assure that the oven stays tight and unified.

2. You'll be happier if you get the pad up and away from any moisture that the soil will have in it. This moisture will wick into your substructure from the soil. This separation will really help minimize the heat transfer into the soil or moisture provided by the soil and this will keep your oven efficient.


brickie in oz 06-27-2012 01:07 AM

Re: Question about ground insulation
Just for you foreigners, Western Australian is made up of two types of dirt, iron ore or sand, Perth is all sand. :rolleyes:

SCChris 06-27-2012 02:37 PM

Re: Question about ground insulation
Ah.. I see, said the blind man..


Faith In Virginia 06-27-2012 04:33 PM

Re: Question about ground insulation
gee AL... and all this time I thought you were the foreigner. ;-)

deejayoh 06-27-2012 09:21 PM

Re: Question about ground insulation
1 Attachment(s)
Jason - I built my oven on top of a wall similar to what you are proposing. After a lot of thought, I poured the slab on grade for the back part, with no added foundation. Some suggested that was the way to go, but end of the day I figured that a 5 x 5 slab of concrete on top of compacted aggregate and soil was probably less likely to sink than one that was suspended on top of some skinny piers unless I poured big footers. and I just did not want to dig that much. Just my $0.02 - but it has worked fine on my soil type so far.

I would look into using some sort of additive in your concrete to keep it from wicking moisture into your oven. I used Xypex - which was kind of pricey, but the slab is dry as a bone even through a very wet spring. I am glad I sprung for that.

brickie in oz 06-27-2012 11:59 PM

Re: Question about ground insulation

Originally Posted by faith in virginia (Post 133999)
gee al... And all this time i thought you were the foreigner. ;-)


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