petec
WFO Team Player
Posts: 232
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Post by petec on Aug 30, 2012 9:49:17 GMT
Hi All, so my base and stand are nearly finished now - most of the blockwork completed last weekend. Hurrah ! I plan to then make a plinth using 450mmx450mm paving slabs, as my base is 1350x1350mm or very close to that. This seems easier than casting a slab. Plan is then to build insulating leyer etc on topn. BUT...... wife and friends have suggested I should now go the whole hog and make it a Pompeii brick job, rather than clay , so it stands up to the bloody awful summers !! ( now that they have seen progress they start to believe this is really going to exist !!! ) Seems like a good idea, but my dilemma is whether my base is big enough for a viable Pompeii build ? Looking at the Forno Bravo plans the bases are much bigger than my 1350x1350mm one. Anyone tell me what size pompeii would be viable ? My plans so far revolve around a 27.5" cob oven design. Still unsure which route to go. Cheers Pete
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Post by bookemdanno on Aug 30, 2012 12:14:31 GMT
My 36" Internal brick oven, sits on top of a 54"x54" (1370mm sq) base. I've trimmed down the insulation slightly, but it should fit...eventually!
I had to make doubly sure that i had the oven in the right spot when i started the build, as there isn't much spare room.
Turkey has built a 30" brick oven too. So you can check his build blog for base size.
I'd say your base will be fine.
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petec
WFO Team Player
Posts: 232
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Post by petec on Aug 30, 2012 12:54:23 GMT
thanks bookemdanno,
It occurred to me after I posted that I could always use a flagstone plinth with an overhang - i.e. larger than the footprint of the stand - and it would look OK and be structurally sound. This would allow a slightly larger oven footprint.
I will check the other builds as you suggest and go carefully. On the hunt for suitable flagstones at the weekend !
Cheers Pete
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Post by turkey on Aug 30, 2012 13:31:14 GMT
the heavy part will be the bricks and not the insulation the clads it, and it will only be insulation that overhangs. You might need to measure and check where the entrance will be and perhaps somehow get a lintel under there but otherwise it sounds like you have plenty of space for a reasonable sized oven,
if you have space to move round the base its a lot easier to use every available mm as you will have the room to render etc, mine is pushing the hearth space but I am pinned in by two fences which is where it becomes hard, if it was an island it would be much simpler.
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petec
WFO Team Player
Posts: 232
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Post by petec on Aug 30, 2012 14:14:20 GMT
....I'm hemmed in too, I have a wall on the right and a fence at the back of my oven stand. Rendering is going to be fun - the fence might have to come down for a bit with neighborly agreement ( i.e. free bread and pizzas for a while ! )
I am using a concrete lintel at the front of the block stand so all good there for some sort of overhang.
Turkey - where can I find your blog ?
cheers Pete
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Post by faz on Aug 30, 2012 14:53:38 GMT
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Post by cannyfradock on Aug 30, 2012 16:48:15 GMT
Pete
If you want a 90cm/36" internal diameter, then you must calculate the thickness of the wall of your dome, plus the thermal blanket, plus the vermecrete layer, plus the final render coat...x2.
Dome wall = 4 1/2" x 2....= 9" Thermal blkt....2" x 2.......= 4" (2" minimum...4" maximum) Vermecrete.....4" x 2.......= 8" Waterproof render 1/2"x2..= 1"
=...... 22"......base is 53" (1350mm)...so you are left with 31 inches...or nearly 80cm of an internal diameter. I say that a 90cm internal diameter is perfect for domestic use.......you can also do exactly the same with a 80cm internal diameter. (some people ask....how many pizza's can the oven take at any one time?....in reality the majority of people only ever cook 1 pizza at a time. It takes about 3 minutes to prepare a pizza, but only 90 seconds to cook one in a Pompeii oven that is up to temp)
As has been mentioned ...oversized slabs will cantelever your base walls to give extra space if needed....or you can still (if not yet done) pour a re-enforced concrete slab on top of your walls, and if you are a D.I,Yer you can extend a little box shuttering to extend the sides of your walls, where you have space.....especially at the front. As long as some re-bar are extended into the area that is canterleving the walls, then you can have an overhang of up to 6 inches.
......these are just my thoughts on an interesting change of planning from a Clay to a Pompeii oven.
Terry
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petec
WFO Team Player
Posts: 232
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Post by petec on Aug 31, 2012 19:26:30 GMT
Many thanks for the tips guys - really appreciate the help and advice.
Havent sourced the slabs yet so may go for a poured slab with rebar. Need to research how the slab, and overhang in particular, would be done.
Rgds Pete
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petec
WFO Team Player
Posts: 232
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Post by petec on Sept 1, 2012 8:39:51 GMT
Quick question before I continue building today.....
I am going to shoot for an overhang but wanted to check that using concrete flagstones on top for the plinth will be ok - seems a thin layer compared to a 3-4" cast/pored slab with rebar. i dont need much overhang with the flags - maybe just 10cm all round.
i see plenty of people using flagstones instead of poured slabs for cob/clay ovens , and it looks very quick - but will it take the weight of the bricks in a pompeii oven OK ?
many thanks Pete
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petec
WFO Team Player
Posts: 232
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Post by petec on Sept 1, 2012 9:05:13 GMT
meant to mention ...
I have 3 steel reinforced 4" concrete lintels, level with , and spanning the top of the blocks - so as long as the flags are OK on top of these there is plenty of strength below. cheers Pete
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Post by turkey on Sept 1, 2012 11:09:33 GMT
with these things its the size of the gap spanned that makes a difference with the material. The flags will take massive weight if they are 100% supported, if they have a gap under them then pressure down could split them.
what is the largest width you have to span?
and if worried could you retro fit a couple more lintels for peace of mind?
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petec
WFO Team Player
Posts: 232
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Post by petec on Sept 1, 2012 12:22:33 GMT
thanks
largest "unsupported" width is about 300mm max.
I guess its the areas where the dome perimeter sits on the plinth that has most downwards force . The weight of the hearth and underhearth insulation is probably not so much.
I will look around for thick pavers first then weigh up options i think. i'm not so confident about making the overhanging frame to pour another slab.
anyway - just about to mortar in the final block course and lintels etc after lunch then a bit of shopping around. cheers Pete
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Post by turkey on Sept 1, 2012 16:34:10 GMT
2 layers of paving at 90 degrees so the joints do not overlap? But nice thick council pavers would be ideal.
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petec
WFO Team Player
Posts: 232
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Post by petec on Sept 1, 2012 18:00:58 GMT
thanks Turkey,
have finished top course and cut in the 3 lintels at 450mm centres including the one at the front lip.
been scouring Wickes and B&Q looking at concrete paving and found best thing seems to be Marshall's 50mm thick slabs from local merchants - had every other size I needed in stock - but not the 450mmx450mm . i reckon 6 450x450 for the back 6 flags and then 3 of 450x600mm for the front row. This gives me exact width for my 1350mm base - and also a 150mm overhand at the front to help with entry arch and flue.
Would be great to get front to back ( including the arches ) - oven dimensions for a 30" hearth oven build if anyone can help.
Anyway at least made some good progress again today.
Rgds Pete
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petec
WFO Team Player
Posts: 232
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Post by petec on Sept 3, 2012 17:27:30 GMT
Hello All again , sorry for the barrage of questions - lots of re-planning going on due to my decision to go Pompeii firebrick oven rather than the original cob build. I am constrained to a 31" diameter interior dimension. I can just get away with it for blanket, vermicrete and render layers - so long as I have an overhang at front of my oven for the external arch and landing. My stand is just about finished - I am using 50mm deep council pavers for the plinth. Few questions I need help with : 1) Can I use a vermicrete and glass bottle layer for my underfloor layer instead of just 4" of vermicrete - I saw this in Kiko Denzer's earth oven book and have been accruing empty bottles for quite a while ( burp!!!) 2) Which insulating blanket spec does anyone recommend - bewildered at the choice on Liam's site. 3) I only bought 27 firebricks for my original clay oven hearth and now need to go big on my next order . How many would I need for a 31" pompeii style build - hearth and dome and landing ? Working out surface area of my bricks I reckon the hearth floor will need 31 bricks allowing for going under the thickness of the dome wall - but obviously I need to go beyond that a little . I want to do herringbone. Really not sure how many for the dome due to mortaring and cutting the entrance. Sorry for all the questions - I have been reading the pompeii threads like mad the last few days though. Maybe we need to move this thread to the pompeii builds section now ? Cheers Pete
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