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Post by darrellme on Jan 19, 2014 17:49:01 GMT
Hi all
I've said hello before, last year I think, but now I am embarking on the build of a 36" corner Pompeii oven. I've only just dug the area for the foundations and I already have a question. I'm kinda using the forma bravo instructions as a guide but there was a little confusing bit in there regarding the thickness of the foundation slab. It mentions that it should be around the 5 1/4 "" in thickness but then also mentions about putting 3" base of pea gravel. So, my question is, is this included in the thickness of the slab, i.e. 3" pea gravel + 2 1/4" concrete = 5 1/4" thickness or should it be added to the total thickness i.e. 5 1/4" + 3" = 8 1/4" in total. In essence I'm wondering whether I need to dig down the 5 1/4" below the ground (leaving 3" above ground level as it mentions in the instructions).
Many thanks in advance.
I'll be posting pictures up throughout the build where possible and I would imagine asking many questions along the way :-)
Darrell
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Post by cannyfradock on Jan 19, 2014 19:53:34 GMT
Hello Darrell
I haven't seen the FB plans (woops) but the gravel and the concrete base/slab would be 2 seperate issues. So in answer to your question.... yes..8 1/2" in total. They would probably go under the idea that the builder is building his oven in his back yard or back garden. Therefore you will still have topsoil or soft ground if you just dug a pit 6" deep. Your floor slab needs a hardcore base for the concrete to be able to support the walls and oven.
They recommend pea gravel...which will be good, but smashed up roof tiles, bricks laid flat or scalpings will give the same effect. Any compacted masonry will suffice for your concrete. Once you have a compacted base it's always a good idea to lay a layer of sand (blinding) then lay a poly memberane over the sand, then pour your concrete. This will stop any damp coming up onto the base...ideal if you want to use the space below the oven for storage.
FB guideline of 5 1/4" is good. Many of us have used 4" concrete with re-bar....or straight 6" of concrete. Make sure you give yourself enough of a footprint when digging out for your base. A 36" internal diameter oven will need a footprint of 1m 20cm wide by 1m 35cm long if you are building a Pompeii oven with 4" walls, 2" thermal blanket and 3" vermecrete.
Hope I haven't confused you.....shout out if I have.
Terry
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Post by darrellme on Jan 21, 2014 12:02:18 GMT
Many thanks for the reply Terry. Ok, so I've been playing with google sketup, which is perfect for helping to realise that I have no idea when it comes to the measurements and will/won't fit. So, the first question I wanted to ask is that I've calculated that the oven width will be approx 59". This includes a 36" internal diameter, 4" firebrick width, 3" FB insulation and a 4" brick outer shell. From that I've then been able to calculate that to have enough room the foundation slab needs to be approx 80" x 80" (as its a corner installation). This seems pretty damn large to me so I just wanted to get some advice as whether the 36" internal diameter oven is too large or whether this is pretty accurate and a recommended size.
Many thanks
D
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Post by cannyfradock on Jan 21, 2014 12:14:29 GMT
Darrell
We've had a few corner builds shared with us on the forum with good detail and pictures diary.....I'll try to find the thread and post it so as we can check any calcs of yours. I'll get back to you later (unless someone beats me to it)
Terry
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Post by bookemdanno on Jan 21, 2014 13:29:52 GMT
You could build a round one, the same diameter as the oven? Build it up so it looks like a tower from a castle! A cone shaped, slated roof on top?
Remember that aesthetically, you want to place the slab one brick course under finished floor height so that it can miraculously disappear! Then it doesn't matter how big it is, so long as its big enough! I found that the best was was to simply sketch it out by hand, to scale on a large sheet of paper and then make a lifesize template from some old cardboard boxes. For all the CAD in the world, you simply cannot beat creating a mock-up of something to get a better feel for it. I work in a very technical industry right now, and believe me, some major mistakes get made by relying on CAD too much. So much that most still create a mock-up to verify the CAD work.
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Post by darrellme on Jan 21, 2014 17:25:54 GMT
Thanks Terry, I'd appreciate any help with finding the threads. I've been through quite a lot of them and couldn't find anything in terms of measurements, etc, in that level of detail.
In terms of the slab being one brick course under the finished floor height, I'm not sure exactly what this means, do you mean that the top of the slab should be around ground level or just slightly above it or should it be below ground level ? Sorry if that seems like a dumb question :-)
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Post by cannyfradock on Jan 21, 2014 20:41:14 GMT
Darrell I'll find more corner builds for you in the next few days, but, at the moment the only one I can find is from the previous poster...our own Moderator...Bookemdanno. ukwoodfiredovenforum.proboards.com/thread/67/suffolk-oven (hope that's OK to post your thread Danno). It's a fascinating corner build with quite a detailed build accompanied with many pictures. It was an interesting build to follow and I always love it when I get the chance to re-visit older builds. As far as your measurements are concerned I totally agree with danno on using a scale rule and hand sketch your design. I enjoy using a scale rule to sketch things out so I'll also make a scaled sketch of your design and measurements and post the result (again...in the next few days). The "one brick below ground level" was Danno's comment.....What he means (I think) is that if you have overmeasured your footprint (80" x 80" does seem too large)...and the slab sticks out further than your support walls, you will have 3" of depth so this can be made up with patio slabs or gravel/turf......I'm sure he will clear that up. Terry p.s.....there are no dumb questions on the forum.....they're all relevant.
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Post by darrellme on Jan 21, 2014 21:20:09 GMT
Ahh ok, the slab will stick out 4" further than the support wall as I'll be then building an external wall using reclaimed bricks instead of rendering it, if that makes sense :-), well, thats the idea anyway's. Many thanks for the help too, very much appreciated
D
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Post by bookemdanno on Jan 22, 2014 13:13:36 GMT
Your foundation will need to support your outer wall too, and project something like two to four inches beyond that too. Make the foundation big enough to do it all in one go. Never be scared to gain clarification on an answer, and never think a question as being a dumb question. Its all too easy to assume that someone "obviously" knows something.
I did a training course once where we had to write down a method for making a cup of tea, for someone who had no idea of it whatsoever. It really opened my eyes, and mind, as to the many possible questions that someone can ask!
Good luck with your build, i'm looking forward to it!
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Post by cannyfradock on Jan 23, 2014 14:05:37 GMT
Darrell I'm pretty pants with sketch-up so here's a rough (...and I mean rough) hand sketch of how I'd go about finding the footprint of the oven. From the rear of the outer brick wall to the furthermost edge of the 1 brick outer arch is 57". I haven't taken into account the extra overhang of the concrete base (as per Danno) to give the support walls the correct foundation strength. 4"? either side, plus you haven't mentioned any vermiculite between thermal blanket and outer brick...this should be another 3" either side which takes the overall measurement to 71". Other things to consider are ....the bricks (if you are using half bricks will be slightly longer than 4" and I haven't offset the outer arch to form a rebate so you're looking more like 75"....your 80" estimate is not far out. This is just a rough sketch so you may find other details not quite exact, but I have scaled the sketch to 1cm = 10cm....i think that's 1:10...? Uploaded with ImageShack.us Hope that helps Terry Attachments:
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Post by darrellme on Jan 24, 2014 11:13:52 GMT
Cool, many thanks, glad to know my measurements aren't that far out. Just a quick additional question, you mentioned the use of vermiculite between the FB and the outer wall, is this required for the thermal insulation then I take it? You're correct I hadn't taken this into account
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Post by cannyfradock on Jan 25, 2014 10:41:19 GMT
Darrell Above is another "rough" sketch that I done a while ago. It's not very good but it might explain my answer. If you are intending to use the outer brick wall as a "housing" so as your oven looks like a little hut...a little like this.. ...(http://img822.imageshack.us/img822/2193/7rdh.jpg) Then you need loose vermiculite fill between thermal blanket and outer wall. This is left in!. You should try to have a minimum of 3" of loose vermiculite between blanket and (lower part of) wall and 3" between blanket and roof trusses. If you are trying to lay an outer course of bricks to follow the line of the Pompeii oven, then you should lay a 3" layer of vermecrete (vermiculite, cement and water) ....or (devil's porridge as we call it)..over the blanket as you would if you were just going to finish the dome with waterproof render. Still confused?.....keep asking!! Terry p.s....click on top image to enlarge
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Post by darrellme on Jan 27, 2014 9:16:58 GMT
Ahh ok, its more like the second option you mention, I was going to lay a course of outer bricks along the same line as the pompeii oven so it retains its dome shape, so it makes sense. Many thanks for that. Its taking me a little while to dig out the foundation pit currently due the number of huge rocks and boulders, but its certainly making some kind of progress :-)
Thanks for the help
D
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Post by darrellme on Mar 31, 2014 10:29:07 GMT
Yay, now that the good weather is finally here I"m going to be getting to grips with the WFO. The hole for the foundations has been dug (took a looong time). I'm also getting my garden landscaped so they said they might as well do the foundation slab too as they are going to be mixing the concrete anyway. They reckon the slab will be around 8" thick as they've had to raise the garden level slightly after the hole was dug. That should be enough to take the WFO without the rebar in it :-). I'll be able to start posting some pictures at some point soon too.
Quick question Terry, is there still a discount at Jewsons for forum members as it would good to start ordering the blocks, etc
Many thanks
D
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Post by cannyfradock on Mar 31, 2014 18:06:19 GMT
Darrell
Great news that your underway......
Perfectly timed post......The Jewson account is still to be sorted. It just so happens that I'm off tomorrow so your post is a good prompt for me to get together with Jewsons to thrash out another good discount account for the members. Hang fire for 24 hrs before ordering. I'll post the new discounts tomorrow
Terry
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