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  #11  
Old 09-10-2012, 02:33 PM
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Default Re: Mortar Mixes

Now you have me confused. Are you looking for a mortar to use in an oven build from brick or a castable refractory? The two are very different things.
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  #12  
Old 09-10-2012, 03:07 PM
GianniFocaccia's Avatar
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Default Re: Mortar Mixes

Shuboyje,

At the risk of stepping on this thread, what is the viability of constructing a brick pompeii dome (quickly) by initially mortaring (homebrew) only the inside-facing joints, and finishing the backside all at once by pouring in a refractory cement 'slurry'?

I know there's a famous Italian oven-builder who does something like this. I was wondering if this is a viable approach for a home-built oven?
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  #13  
Old 09-10-2012, 05:01 PM
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Default Re: Mortar Mixes

It's a speed thing. The italians feel the entire dome needs to cure together and to do so the dome should be built in one day(their logic not mine). I'm sure the speed is just as much a factor for economic reasons.

By using this technique and a sand form the dome can easily be built in a day. I used a modified version in my oven, and it really is lightning fast. To do it you do not mortar between bricks within the same course, you only mortar between the courses(I have a graphic I made to explain this somewhere). This leaves the dreaded triangular gaps that many Pompeii builder taper bricks to avoid as empty voids in the bricks work. Once the entire dome is formed this way a slurry of some sort of refractory material is poured over the dome to fill all the gaps and complete the dome. In the US I could not find a product on the market made to be mixed wet enough for this procedure, so I used a stiff mix of castable refractory and rodded it into each gap.

As for your question about facing the joints in homebrew and then back filling them with commercial refractory mortar, that is the opposite of what you would want to do in my opinion. One of the problems with commercial refractory mortars in dome ovens is that they are generally made for 1/8" mortar gaps. Homebrew mortar does a much better job with the larger gaps. So if you wanted to do a hybrid system commercial refractory mortar in the small gap inside the oven and then homebrew as the gaps widens at the rear would be a better option.
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  #14  
Old 09-10-2012, 07:12 PM
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Default Re: Mortar Mixes

An Italian friend of mine built a red brick oven using this technique. He used half bricks, roughly cut with a bolster, untapered, laid up against a sand dome. The bricks had lots of wooden wedges sticking out on the outside. Once he'd gone up a few course the bricks were back filled with home brew, removing the wedges at the same time. It is quick and easy and probably produces as good a result as meticulously cut individual bricks.
Unfortunately he did not take my advice and failed to insulate under the floor. He subsequently had to retro fit some insulation under it later.

Last edited by david s; 09-10-2012 at 07:14 PM.
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  #15  
Old 09-11-2012, 12:31 AM
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Default Re: Mortar Mixes

David S .......speaking from experience on my first oven I tend to agree. Sure on my current build I will use my bricksaw to some degree to reduce the gaps inside the dome .... but plenty of homebrew elsewhere and homebrew "capping" the outside, before blanket insulation will give an oven a bit more mass. Reduce the airgaps and one whole mass that's effectively entomed by the outer insulating and render layer should be ample methinks.

Spinal I was thinking refactory mortar for a while but home brew seems to clinch it for me..and my first oven wasn't even homebrew and its results after 4years use was surprisingly minor cracking, no flaking etc......mmmmm.
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Last edited by Bacterium; 09-11-2012 at 12:37 AM.
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  #16  
Old 09-11-2012, 03:45 AM
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Default Re: Mortar Mixes

It's not the cracking/flaking I'm worried about (in OP mixes) tbh - it's the refractory properties.

I'm cutting my bricks with a bolster; they will not be angled in any satisfactory way. There will be (a lot) of mortar between joints. I may use a grinding disk to remove some sharp angles, but the way I figure the bricks are cut in half - the "smooth" edges (i.e. the non-cut face) goes inside the oven and the cut face is buried under layers of insulation... so I'll have triangles inside... but I'm not too concerned...

Based on the pdf I posted before, by changing the mix of chamotte (more coarse chamotte for thicker joints) you can fill some pretty thick joints... I'm ordering chamotte all the way to the 6mm grain size, so shouldn't have an issue filling my triangles.

The larger gaps will essentially be a castable refractory mix - coarse+medium+fine crushed firebrick grog, fireclay and HAC. Total alumina content will be proportional to the ingredients, so between 36% and 42% (if I use cheap HAC - if I were to go all out, kerneos do some with 80% alumina... but that's harder to source - and more expensive)

Dome will be built in a day... that's the plan! (and though I am Italian, I'm doing it for time reasons, not because I thought that's what was needed!)

1st layer of floor insulation has finished curing, and is now drying - 4" of vermicrete. Once it's dry, it will get 4" of bio-board (like ceramic board, but with a higher temp rating and not carcinogenic).

TBH - I just don't see the value of homebrew bar its "ease of use".

It's not substantially cheaper (using UK suppliers) and has negligible refractory properties. Even the ease of use is contestable, as I need to get the entire dome built in a day... so the curing speed of HAC will be beneficial (planning on getting a helper to mix while I mortar - one "ring" at a time using a foam/wood form for the last rings).

M.

Last edited by Spinal; 09-11-2012 at 06:27 AM.
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  #17  
Old 09-12-2012, 12:13 PM
Faz Faz is offline
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Default Re: Mortar Mixes

Unless you're a skilled/experienced bricklayer I think you'll find the use of HB beneficial, as it takes a while to go off fully meaning you can reposition bricks if necessary.

Are the other mixes you mention more rapid setting?
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  #18  
Old 09-12-2012, 03:02 PM
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Default Re: Mortar Mixes

OP based mortar sets quite slowly - iirc it takes a week or so to fully cure OP cement.

HAC based mortar will set much faster - 40 minutes for an initial set, and 48 hours until cured to full strength.

That said, if you want HAC to set faster, add some lime (which with OP acts as a retardant). If, instead you want HAC to set slower, trisodium citrate is your answer (I'm told).

M.
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