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Post by isolec on Aug 5, 2012 10:54:40 GMT
Just looking at how i am going to form the arch of my vault. Is an arch weakened by having an even number of bricks in it i.e. the joint is in the middle as opposed to having a keystone?
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twobecks
valid member
Cooking like a mad man
Posts: 55
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Post by twobecks on Aug 5, 2012 12:02:04 GMT
Isolec,
I ended up building two arches on my project.
The first arch I thought I could get away without having any cut bricks, as I wasn't confident doing this. I used a former made from two pieces of mdf sandwiched between a foam filler. The arch had a single keystone, albeit just a standard brick, and it looked okay. After doing some more research, it became obvious that I should have used a few wedge cuts to get the "turn" on the arch and the fillets of mortar between the bricks were huge. I decided to bin it and try again.
The second arch used the same former, but the bricks were cut down to get the curve more natural and without using vast quantities of mortar between the bricks. This again had a single keystone, but I think you can probably get away with having an even number of bricks so long as they are not "flat" in the arch - that is to say they meet at a bit of an angle.
My build thread in modular ovens has quite a few pictures of the arches and the thinking behind the former. It's in the Facebook link.
Good luck mate!!
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Post by cannyfradock on Aug 5, 2012 12:05:46 GMT
Isolec If the arch is shallow and/or the bricks are evenly spaced(with the exact same sized perps in between uncut bricks)..then it doesn't matter as the integrity of the arch will not be compromised regardless of where the bricks lie on the top of the arch. It always does look better aesthetically if you can leave the top brick central to the top of the arch......or have the perp directly central leaving the 2 top bricks evenly spaced either side of the central point. Where a more severe curve is used in a small arch and the perps will be too big to use uncut bricks, then either all of the bricks will be cut in a wedge shape ...or 1 keystone will be cut which WILL be directly in the center of the arch. Terry Addition.....interesting link to arch construction www.earth-auroville.com/avd_construction_en.php
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Post by isolec on Aug 20, 2012 7:51:10 GMT
Is Vermicrete just Vermiculite and portland or is there some sand in it? Oven chamber is built and i now thinking about insulation. i will try and post some pictures soon!!
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Post by turkey on Aug 20, 2012 9:01:56 GMT
just vermiculite and Portland, but in truth you can use any binding agent, so lime or a wet clay slip if you prefer. With cement you can get quite high ratio of insulation to binder you want 5+ vermicrete to each 1 cement.
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Post by isolec on Aug 20, 2012 15:06:59 GMT
Thanks Turkey - think i'll stick to portland. I hope its better to handle than the homebrew!!!!
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Post by turkey on Aug 20, 2012 15:59:21 GMT
if you found homebrew hard to work with I can only wish you the best of luck as I found vermicrete is truly a pain to work with, especially when trying to stick to ceramic fiber blanket, if going direct onto a brick vault it might be easier. Once you get going its not so bad as after you leave the vertical part of the brick work gravity helps a little rather than trying to hinder you.
My advice is buy plenty of disposable latex gloves and get stuck in with your hands.
Have a second bucket of water to clean your hands in prior to each mixing or needing to do anything else.
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Post by robinhoodoven on Aug 21, 2012 7:03:46 GMT
.. Can anyone give me the right mix for "FIRE CLAY + SAND + CEMENT" .. for teh outter sealant of our new oven .. Thank You .. ! ! ! !
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Post by isolec on Aug 21, 2012 9:21:38 GMT
Hi Turkey
I am going to do what many others have done - skip the fire blanket and go for a god thickness of vermicrete before rendering. The plan is to shutter the vertical parts and just poor it down and in. Presumably as we are not looking for high structural strength i can make it fairly wet so that forms well in the shuttering.
Had a small firing in the uninsulated vault night before last - more for curiosity than for drying. I was amazed at how long it took for the heat to disipate to the outside of the storage blocks. I shouldn't be suprised really as i was well aware of the high thermal mass in the storage heater blocks. Modern kiln bricks are relatively low thermal mass and should come to temperature much quicker. I've not seen any posts re the benefits / disadvantages of HTM over LTM. I am guessing that Storage heater block constructions will take significantly longer to come to temperature but will take longer to cool.
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Post by isolec on Aug 21, 2012 9:31:11 GMT
Hi Robinhood
Sand, cement, fireclay and lime should be mixed in the ratio of 3.1.1.1. However this should be used as a mortar for your heat bricks and not as an outer sealant. The outer sealant if not a brick and roof should be rendering
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Post by tonyb on Aug 22, 2012 11:51:41 GMT
It depends what you mean by HTM and LTM. If you mean high alumina as opposed to mid alumina (standard firebricks), I'm not sure there are any advantages for a domestic situation. If you are talking about low alumina (often called thermal insulating bricks), we've discussed this previously, including the thermal properties you highlight. On balance, I think the general consensus was that the medium alumina bricks were best, but not overwhelmingly so.
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Post by isolec on Apr 29, 2013 7:42:55 GMT
Hi All - long time no post. Back on the oven again. Landscaping the garden has taken priority for the last few months. I shuttered and covered the heat bricks with 4" vermicrete at the weekend. Just started to think about the final render. I am a little concerned about mechanical strength with just the render on top of the vermicrete. The vermicrete, whilst firm does not have a great strength and my worry is something hitting the render and it cracking - any thoughts?
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Post by turkey on Apr 29, 2013 14:30:09 GMT
HI Isolec, vermicrete may be a little delicate and flaky to the touch but it does have remarkable compressive strength, the render on top will protect it from abrasion and its already fine under load so I do not think you have much to worry about. I have stood on my rendered oven a few times with no ill effects to it. You do two coats when you render, the first scratch coat and then the final skim, this is a pretty tough layer in itself. I am sure Terry or someone with better knowledge on render systems can better alleviate your fears but I do not think you will have any issue as long as you do not go about tossing cabers you should be fine
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Post by isolec on Apr 30, 2013 7:53:06 GMT
Hi Turkey, sounds like i am being a bit cautious so i'll stop worrying. I've done a bit of plastering in the past but never rendered. When i trawl the net there are as many different recipes for the render as there are articles - some use sharp sand, some plastering sand, others a mixture of soft and sharp sand, some use lime, some plasticiser, some retarder, some put a waterproof in both coats others only the top. I am begining to think it is not an absolute science.
Also not sure how to handle the edges of the external corners. Beeding is fine on the straight verticals, but what about where the roll of the roof meets the vertical back. I cant see how i would make a rolling beed. Perhaps i should go for soft radius on all edges.
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Post by turkey on Apr 30, 2013 14:55:08 GMT
yup well and truly over my head, I was in a rush so I just mixed sand I had with cement and used waterproof in both coats, I did not do anything clever at the joints and I know mine does take on a little water at the outer edges so I know its not perfect.
Hopefully someone with some actual rendering experience will be able to give better advice on the specifics.
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