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  #21  
Old 02-07-2012, 01:22 PM
GianniFocaccia's Avatar
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Default Re: 39" Stargate Pompeii

Hey Aidan,

Nice looking arch! You are obviously blessed with a high level of dexterity and coupled with your layout skills and keen eye, you will no doubt have an oven to be proud of. What's nince is that as you fit each brick (arch and dome) together, you will know intimately what minor tweaks to make and can build a truly custom oven. I know it takes time, but hell - you only gotta do it once I say.

FWIW, I bought a continuous rim 4" masonry blade for my angle grinder thinking it would give me a smoother cut. Not so.

Quote:
Gianni - I read somewhere that you added more lime and clay and less portland for a more sticky mix. would it change the ratios or how precise were your measures?
As fas as I know, the homebrew recipe relies on measurement by volume. This is what I used. Once I found out that the role of portland cement is to act as a guaging material and is prone to failure over repeated 500F thermal cycles, I took it upon myself to slightly modify the ratios in a very unprecise process (eye method). Given that Francis' (Switzerland) dome was built using mortar of sand and fireclay only and is still going strong after several years, I believe the ratio is not all that critical.

Hope this helps. Keep the pics coming.

John
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  #22  
Old 02-09-2012, 04:09 AM
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Default Re: 39" Stargate Pompeii

Hi Gianni
Quote:
blessed with a high level of dexterity and coupled with your layout skills and keen eye
Not too sure about that - I think you left out a smiley there! Already I feel I might have to give this another go to get it right. I am still confident though about the dome to arch integration though

Quote:
Once I found out that the role of portland cement is to act as a guaging material..
I'm not sure what exactly you mean by "gauging material". I thought it's main purpose was as a hardening agent. The mix seems to work Ok. I tried to separate two brick pieces with today my hands and they held strong.

So if Frances used no portland - just sand and FC her oven should be easy to dismantle. Isn't that a kind of daub mix. It certainly should mean any cracks will be in the joints rather than the brick itself. I read her build and was impressed by the mosaic covering - but I must take another look.

I planned to start building but the rain is back Back to browsing.
Aidan
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  #23  
Old 02-09-2012, 09:02 AM
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Default Re: 39" Stargate Pompeii

Quote:
I thought it's main purpose was as a hardening agent
That's what I thought too. I am by no means knowledgeable on this, but it has been explained here that the role of mortar is to keep the bricks apart, not joined together. It was also explained that portland's role in mortar is to provide body/resistance (guaging) for proper alignment when squeezing a brick into place.

Portland cement does bind all of the mortar ingredients together, but with it's non-refractory properties, loses it integrity over time and thermal cycles. This is where the lime takes over.

I would think that Frances' dome and mortar has gotten stronger over time because of the thermal cycling. Just my thoughts.

John
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  #24  
Old 02-10-2012, 07:20 AM
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Default Re: 39" Stargate Pompeii

I ran into a small - maybe not so small - problem. When I did some testing of the mortar mix the other day I thought the mix felt "gritty" and found some largish bits of grit (brick?) had got in it. Since I mixed it on a concrete slab near where I was cutting brick I assumed I had picked it up from there but today I mixed some more and found the same problem. It was obviously not the lime, sand or cement, so I examined a trowel of the "fireclay" and it seems to have quite a lot of grit mixed through. How fine should this stuff be?

The bag in which it came was sealed although without any markings so I can't say if it was some particular grade? Now I don't trust that clay at all - see pic. Note the rather large piece separated out at the top centre which looks like a piece of brick to me.
Anybody else have a problem like this?
Aidan
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39" Stargate Pompeii-photo0283.jpg  
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  #25  
Old 02-10-2012, 11:12 AM
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Default Re: 39" Stargate Pompeii

Don't throw it away, you can simply sieve out the course stuff.
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  #26  
Old 02-10-2012, 11:25 AM
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Default Re: 39" Stargate Pompeii

As I understand it, the largest particles in your mortar should be smaller than your smallest brick gaps..


Chris
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  #27  
Old 02-10-2012, 11:33 AM
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Default Re: 39" Stargate Pompeii

Quote:
Don't throw it away, you can simply sieve out the course stuff.
Thanks David - I will try that. I also got on to the seller - they are getting back to me on Monday - maybe get another bag for free.
Quote:
As I understand it, the largest particles in your mortar should be smaller than your smallest brick gaps..
Yes Chris I would agree - not the case in this clay though. Maybe with sieving as David suggested I can use it - but I feel it should be "workable" not this coarse!
Aidan
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  #28  
Old 02-10-2012, 12:56 PM
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Default Re: 39" Stargate Pompeii

Try an old window screen. If your careful you can clean it up and put it back in the window before she finds out that it is missing

Here is one way.
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  #29  
Old 02-10-2012, 07:07 PM
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Default Re: 39" Stargate Pompeii

According to tscarborough, the ideal mortar has a variety of aggregate sizes in it, much like the jar with multiple sizes of rocks, pebbles, sand, etc. This keeps the portland to a minimum, and if the aggregate is small chunks of firebrick, even better.
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  #30  
Old 02-11-2012, 03:33 AM
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Default Re: 39" Stargate Pompeii

Quote:
Originally Posted by Gulf View Post
Try an old window screen. If your careful you can clean it up and put it back in the window before she finds out that it is missing
Luckily we don't really need window screens here. I guess we don't get a lot of balmy evenings with tropical insects etc. zooming about, and our mosquito population is virtually non-existent. I was tempted by some kitchen utensils but thought better of it and bought a sieve (with a few different grade inserts) for a few quid instead
that brickdust looks good. Mine is all over the place though because of the grinder.

Gianni
Quote:
According to tscarborough, the ideal mortar has a variety of aggregate sizes in it, much like the jar with multiple sizes of rocks, pebbles, sand, etc. This keeps the portland to a minimum, and if the aggregate is small chunks of firebrick, even better.
This stuff will work with larger joints Ok I suppose - but the smaller and variable widths I will need something finer. I guess I can make two mixes at once

thanks for the feedback - really appreciate it
Aidan
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