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Post by marudge on Mar 17, 2013 15:15:34 GMT
Planning my oven build for Spring 2013. I've attached a picture of the site where I propose to build it. First question is do I need to cut a hole in the slabs to put a concrete slab in place or will it be sufficient to build on? The slabs were laid well and are on solid ground but they do not have a solid layer of concrete underneath them - just five big 'blobs'. Attachments:
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Post by h12rpo on Mar 17, 2013 18:39:38 GMT
Someone will be along in a mo to answer your question........... Not sure if I'd get any work done though if I had a view like that !
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Post by cannyfradock on Mar 17, 2013 19:22:07 GMT
Hello Marudge
I wouldn't take a chance on the slabs myself if they have been laid with just dabs of compo. A 42" oven will have a fair bit of weight. I would lift the slabs in the area where the oven is going and lay some decent concrete underneath. You can then re-lay the slabs, but lay them on a full bed of concrete. If you use small 6mm chippings for the concrete at a ratio of 4 chippings 2 sand 1 cement....this should be fine. The spread of your support walls will stop the slabs from cracking.
I know the gurus at FB use fire-board a lot, but I've never used it myself....sorry. I always lay fire-bricks on top of insulating blocks.....on top of the concrete slab. The top of your oven should always be sealed (waterproof render, tiles, masonry paint etc). The damp the FB guys are probably talking about is rising damp. I always lay a DPC (damp proof course) on top of my first course of bricks to stop this. I also lay a DPM (damp proof membrane) under the concrete base.(when I can)
The finish is down to you. I haven't built a housing myself but it's a lot better than just waterproof render, plus with a housing the vermiculite which goes over the fire-bricks can be just loose filled into the void the housing creates.
Hope you get more feedback on your questions.
Terry
P.s....made a double post as this is your main build thread.
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Post by cannyfradock on Mar 18, 2013 8:12:00 GMT
Marudge Just re-read your post. If there is concrete under the patio then just re-lay the slabs as suggested. Just to contradict myself.....on my 2nd build I laid directly on concrete pavers, but I know that the sub base was well compacted with scalpings and 1/4 to dust and "wacked" several times. If you look at the 4th pic in my build...... ukwoodfiredovenforum.proboards.com/index.cgi?board=pompeiioven&action=display&thread=677 ......you will see how the dpc that was laid on top of my first course of bricks is stopping the rising damp. On the following pic you can see that I've also laid dpc ON TOP OF the walls also, before pouring my slab. Terry
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Post by bookemdanno on Mar 18, 2013 13:03:33 GMT
Wowzers! What a view! I echo "The main mans" views. Slabs laid on "dabs" will only ever take foot traffic. Its a quick, cheaper way, but not the best way to lay paving. Lift an area up, dig out an area for a pad allowing the level to be an Inch below the underside of the original paving and build up your base. Then trim the slabs back into place. The Inch gives you a mortar bed to re-lay the slabs.
What a wonderful place to live! Is that the South Coast?
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Post by marudge on Mar 18, 2013 20:11:45 GMT
Thanks for all you replies - that's helped my planning. I now have added the task of digging up paving slabs, clearing and laying a concrete slab before I start the build and then relaying the paving slabs. I am a great believer in putting in the preparation to give the best end result. Yes, the view is great. That is why I thought it was a great place for an oven. It is the South Coast 'bookemdanno' - that is looking over St Austell Bay towards Gribben Head. 'Cannyfradock' - have you got a URL for insulating blocks. I need to check that out before I decide which way to go? Thanks
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Post by turkey on Mar 18, 2013 21:03:17 GMT
insulating blocks is just the generic term, thermalite / breeze blocks are what Terry is referring to. They have high insulating properties can take the compressive weight of the oven on top, cheap and quick to lay. Downside is they are thicker than the specialist boards the FB boys use. Terry has the build he was referring too here with all the gory pictures ukwoodfiredovenforum.proboards.com/index.cgi?board=pompeiioven&action=display&thread=677
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Post by bookemdanno on Mar 19, 2013 12:40:53 GMT
Ahh yes, had many a trip further down the A30 Perranporth way, but can always remember the old China Clay workings visible from the road as a driving landmark and a visit to The Eden Project of course! Always partial to a pint of Tribute too!
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Post by marudge on Mar 23, 2013 20:30:56 GMT
Been working through the forums some more, trying to understand the build better, put some drawings together and a materials list. I am intending building a 42" Pompeii with all bricks tapered and bevelled. This should reduce the amount of cement needed when building the dome to an absolute minimum. I have decided to insulate under the cooking floor with 50mm of Calcium Silicate. I am looking to build a roof over the dome which I can fill with insulating material. Most materials I will get locally e.g. sand, cement, blocks, etc but I intend to order my bricks, insulation and fire cement from Kilnlinings. Before I place an order I would appreciate a sense check on volumes. I am looking at: - 2 x LBP HT Blanket 1200GD – 7.32M - 610 x 25mm (Density 128kg)
- 3 x Calcium Silicate 1000GD 1220 x 500 x 50mm
- 220 x Fire bricks 42GD - 230 x 114 x 76mm
- 4 x 25Kg tub Cement - KLW.A.S.C - Firebrick Cement - Heat resistant to 1600CCement
I think I may have overdone the cement and I am not totally sure about the HT blanket. Advice appreciated Thanks Mark
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Post by rivergirl on Mar 23, 2013 21:46:44 GMT
As the others have said , fantastic view!! Really looking forward to the photos of the build!
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Post by cannyfradock on Mar 24, 2013 7:09:55 GMT
Mark
I've never used the calcium silicate board. I always use insulation blocks or before that a mix of vermiculite cement and water mix. I know the guys on the FB forum use the CS board a lot.
I don't think you've overdone it with the thermal blanket. It's only 25mm thick and the normal depth is 50mm.
A lot of people have come unstuck using fire-brick cement because it can only be used very thin (check with Liam...or check his site data).....if you are confident that you can cut all your fire-bricks to fit perfect, then you will be OK. The problem using fire-brick cement is that if the thickness of the cement is more than 5mm? (check data) ....the stuff doesn't set. It may be an idea to buy 1 or 2 bags of powdered fire-clay, so if you DO have an area where a heavy mortar bed is needed, then you can mix up a small batch of refractory mortar using a ratio of 4:1:1:1.....sand, cement, clay and hydrated lime.
Terry
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Post by tonyb on Mar 25, 2013 17:01:44 GMT
I used 200 bricks (with just a couple spare) for a 42" internal diameter oven and small flue stack, but I only cut the 2 vertical faces and then not fully, ie just to lock the bricks. If you are planning on cutting all 4 faces to the small tolerances required for using fire cement, that's quite a task. Most of the pompeiis on this site are built without any cutting of side faces, and whilst I think some cutting of side faces does improve mechanical stability, none of this is actually visible so people won't be able to see your handiwork as its covered by the insulating blanket and vermicrete. I don't want to put you off this approach as a cement free build is probably the ultimate measure of the wfo builder's skill but it will take a lot more time and skill for arguably little mechanical/thermal benefit.
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Post by turkey on Mar 25, 2013 19:37:45 GMT
if you are building a roof over the dome to backfill with vermiculite to make a sort of house (4 walls etc) then the blanket insulation is a waste of money as the vermiculite is perfectly good. The blanket is better when a thin layer is required, ie when making an igloo oven as you don't want a super thick crust.
4 tubs of cement seems a lot to me, that stuff only really sets to a joint width of 3mm so you have to be extra exacting when doing all your cutting, I would suggest ordering less of that and get fireclay also, you will need the fireclay to dry lay the hearth bricks and I would also use homebrew to back fill the outer part of the dome, use the klwasc for the inner face part but where the bricks have bigger gaps keep some homebrew to use.
other than that the brick count seems ok with a sensible wastage buffer and the underfloor insulation is ok, perhaps make a thin layer or insulating concrete under it to be sure as that's what the US boys do and it seems you are following their build plans :-)
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Post by Belfastcity forester on Mar 27, 2013 2:43:51 GMT
A few pointers from my recent efforts. Don't be tempted to turn firebricks thickly, aim for minimum depths by stacking on edges. 4.5" wall or floor is really twice as thick as you really need for thermal capacity unless you burn daily for hours. I found that it's possible to guess, use eye to slice a slight diagonal and camber, freehand with brickies 12" saw. the 230mm angle grinder is hard to keep straight and dangerous kickbacks. Fire cement with shards wedged in as packing works well, u can do it with 2 maybe 3 tubs. Try to avoid any cement joints on the insides, it's possible if you buy arch bricks rather than std straight ones. Blankets. You can't have too much insulation top or base, 50mm silicate board is a minimum if u want a cooking floor. The 2xblanket reduces max temp to 250degC you need to enable render, and it would need the similar cash for the equivalent in 4+ bags of vermiculite so go for 75mm blanket =250mm loose vermiculite= 350mm perlite concrete
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Post by marudge on Mar 27, 2013 10:51:41 GMT
This is really helpful - thank you to all those that have contributed. A few things remaining: - tonyb - I am looking to cut 3 sides, not 4. Have I got that wrong? The attached PDF shows what I am intending to do. I know the accuracy of the angles is probably cloud cookoo land but I wanted to work out the theory first.
- Belfastcity forester / turkey - I will be building a roof over the dome so does this mean I can dispense with the blanket completely? I am not quite clear - thanks. The thickest blanket Kilnlinings do is 50mm too, not 75mm.
- turkey - the thin layer on insulating concrete under the board sounds a good idea - I had not read that. Do you know how thick they do it?
Thanks again for all your help Regards Mark Attachments:
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