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Post by Calaf on Feb 6, 2012 22:00:08 GMT
Porca Santissima!
Due to the design change of moving the storage heater blocks to the floor and using firebricks for the rear wall I have lost 21mm. I forgot to accommodate for this by positioning the Calsil board a little forward. It doesn’t sound much but my design is compact with tight tolerances. Now the space between the rear wall and the cement board outer wall will be just 50mm. Enough for the ceramic fibre blanket but maybe not the Rockwool backup. Perhaps I can squish it down enough. Vedremo.
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Post by Calaf on Feb 6, 2012 22:00:49 GMT
My build requires 9 half-bricks, 2 in the rear wall and 7 at the door. I was a bit worried about splitting these firebricks as I have read here that they are a bugger to cut. I needn’t have worried at all. My extravagant £4 diamond disc cut through them like butter. I suppose the fact that they were so wet helped. I will use the leftover half-brick by cutting it diagonally and placing the splits either side of the inside entrance to make brushing out ash easier.
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Post by Calaf on Feb 6, 2012 22:01:15 GMT
I’m getting as excited as a Nun at cucumber stall. First two courses are down and I'm strting to get a feel for the oven's size now. I pushed mortar into the perimeter where the blocks meet the Calsil skirt, then brushed fireclay into the cracks between the blocks. The join of the skirt to the base has also been sealed to prevent any hot air venting out from the air pockets under the hearth. The firebricks are incredibly wet, even after spending two days indoors stacked in front of a radiator. Some have a bit of algae on them. I’ve kept the mortar joints thin, I know this ready-mix cement has a reputation for cracking, by handling it like floor tile cement. I am pointing the outside with a wallpaper scraper and the inside with my specialised tool, a digitus secundus manus. Because the heater blocks are butted dry but the firebricks have a thin mortar joint the front edge of the wall sits a few millimetres forward. This is all part of the plan as the aperture arch will then sit slightly over the CalSil skirt.
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Post by Calaf on Feb 6, 2012 22:02:48 GMT
Looks lovely so far Calaf, but i'm a little concerned about the fact that your brickwork doesn't have staggered joints and the rear wall isn't tied into the side walls. Especially as you're going to have forces wanting to push the side walls outward once your setting your arches. You've been very thorough so far, so maybe i'm a bit off... nice tidy work so far, and pretty good for the time of year! Hi Bookemdanno. Thanks for pointing that out. About the rear wall, I honestly hadn’t considered tying the rear wall’s bond to the vault, which does seem insubstantial now you mention it. I will incorporate something in the final course like some wavy galvanised steel wire. Thanks for the tip-off. About the arch piers, I can see what you mean. Because the arch is not a full semicircle the thrustline is angled to push outward against the wall. I’m not an engineer, so I lack the knowledge to work this out correctly, but I’m thinking each of the four arches will be 9 bricks with a dry weight, including mortar joints, of approximately 45-48Kg, each bearing down on the support walls with <24Kg static load entering the springer at 45 degrees, so the horizontal force is <12Kg per arch, or <48Kg over 92cm of wall. This probably wouldn’t be enough to topple a mortar bonded wall with a height only 1.3 x its thickness but for security the base of the wall will be buttressed with ‘vermiperlicrete’ because it does overlap the CalSil, which I don’t feel confident about mechanically. I'm probably talking twaddle but the resident brickies will put me straight.
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Post by Calaf on Feb 6, 2012 22:03:31 GMT
I had a long hard think about the above problems last night.
The rear wall is under little stress, just compression, so two short ties in the final course should suffice.
For the arches, one idea was to incorporate a steel wire along the length of each wall and tied to the rear wall to resist any tension exerted by the arches. But I suspect this might introduce weakness as the thermal coefficient of steel is far greater than brick.
The weak point in the wall is the bond to the block floor which is only 80mm of its 115mm thickness, plus 25mm of calcium silicate. I think it will be sufficient to use a vermicrete abutment to the first course. The forces are not sufficient to cause a problem for the second course.
I could crash and burn with this over-engineering.
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Post by Calaf on Feb 6, 2012 22:04:11 GMT
The vault's segmented arch. Making a template for the arch form.
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Post by Calaf on Feb 6, 2012 22:04:41 GMT
And here's the arch form made from 18mm plywood. The gap in the front arch is for access to the shims at the back.
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Post by Calaf on Feb 6, 2012 22:06:06 GMT
Calaf I love your diagrams and posts and WISH I had the time to discuss your detail.....in detail ( I must make the time). I like the way you are designing your arch formers. As a bricklayer I calculate the height of the support walls then the springing point, then the curve of the arch and transform all that to plywood etc....and cut my arch formers.....I then mark out the former to make it work bricks.....or space the bricks accordingly...or make a keystone to fit the gap at the top....Your system looks much easier. Terry Thanks for the encouragement, Terry. I don’t know about my way being easier, more convoluted perhaps. Here is what I did. My starting point was the bricks. I knew I wanted to span 600mm with a low vault, and not a semicircle, using 76mm bricks so I figured I would need 9 or 10. A rough drawing confirmed 9 looked aesthetically more pleasing. Then I used my own simple formula to calculate the offset of each brick… Sa1-Sa2 / (Bn-1) Where Sa = Spring angle in degrees, Bn = number of Bricks. In my case I wanted a segmented arch with a simple 90 degree turn. Result = 11.25 degrees. This is then easily transferred to paper. I think this method is better for me as I don’t have access to a table saw to accurately cut bricks. I’m using a 115mm angle grinder, hand held, so wouldn’t be able to cut a custom keystone with confidence. BTW, I’ve also found a cheeky way of avoiding cutting the skewbacks.
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Post by Calaf on Feb 6, 2012 22:07:38 GMT
Calaf, A piece of advice regarding your formwork. You may find it easier if your form isn't a perfect arch, but is 9 straight edges spanning the arch. This will help your bricks sit on the form much better and avoid rocking. I personally found this easier not having laid bricks before. Although I would be tempted to leave your form as it is given how wellit's made! ) Hi DuncanM, great idea. The picture doesn't show it well but in fact that’s what I did Although the jigsaw and subsequent sanding rounded the corners off there should be enough flat to steady the brick.
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Post by Calaf on Feb 6, 2012 22:08:48 GMT
The corrugated roofing I was using over the project lets in too much moisture in this damp weather. So I switched to a polytunnel sheet which seems to have worked better. The "air-setting cement" doesn't seem to be in any hurry to set in air.
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Post by Calaf on Feb 6, 2012 22:09:59 GMT
I have designed the vault to be fairly low to impart some of the Pizza oriented properties of the Neapolitan round oven design. However, the inclusion of a quarry tile floor means the oven’s apex will be under 300mm high. The vault height should be 1.6 X the door height (1/63) so to fit my 195mm chicken brick, 195 x 1.6 = 312. Therefore 300-310mm is my target. To solve this minor problem I am adding height to the side walls with a row of clay roofing tiles before starting the arch. At this point I’m starting to get nervous about building those arches as it is outside of my comfort zone. My bricklaying skills are worse than a drunken cowboy.
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Post by Calaf on Feb 6, 2012 22:10:43 GMT
I originally planned to start the segmental arch at 45 degrees using some plywood wedges and filling the joint with clay brick cuts. However, giving it some thought, the dead load of the arch generates shearing force that is converted to downward compression here, making it a critical point. Far better to use a properly cut skewback and minimise the use of the dodgy ready-mix cement. Not trusting my ability to cut bricks correctly I found the solution: This is a PL3.1 Plinth Stretcher. A bugger to source but I serendipitously stumbled upon a pallet at Selco. They are slightly shorter than the Firebricks so I bought 10. Plinth bricks x 10 ---- £20
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Post by Calaf on Feb 6, 2012 22:14:20 GMT
Skewbacks are complete. Arch ready for liftoff. There is salt leeching from the mortar joints. I'm assuming that is normal.
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Post by Calaf on Feb 6, 2012 22:15:40 GMT
Calaf Your build is starting to get real interesting.... Salt extruding from the mortar joints is usually caused by rainwater that has entered the aggregate of the bricks when they were made....or bricks that have been left uncovered for a long time ..or sand for making the mortar which has been saturated with rain water...Efflorescence!!! It can be chemically treated, but often will still return until it is treated 2 or 3 times. The salts in the wall will eventually eak out of the wall naturally. Myself, I would just clean with fresh water every couple of months....the salt crustations will soon disappear. Terry
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Post by Calaf on Feb 6, 2012 22:16:16 GMT
I said to the wife, why go through all this bother and expense for a pizza oven when you can buy a Presto Pizza Oven for a fraction of the price. She just gave me one of those looks.
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