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Old 11-28-2009, 07:38 AM
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Cool mortar question

I am building my first wood-burning oven; I have been using a book “The bread builders by Daniel Wing & Alan Scott” and the web, thus far things have been going great. This week I would like to lay the oven wall firebricks and arch bricks. The book states refectory mortar or a mixture of 10 parts mortar sand, 3 parts Portland cement, 1 ½ parts fireclay. This will provide a hardened mortar that will have an expansion rate similar to the firebrick as well as making it sticky. It would be a shame to get my bricks; insulation, cladding and façade complete only to find the oven mortar fail. There appears to be a thousand opinions out there should I follow the book?:
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Old 12-01-2009, 09:05 AM
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Default Re: mortar question

Paul,
You have stumbled onto one of the most discussed topics on the forum. Use the search tab to search for refractory mortar poll. It will give you plenty of information, but may not answer specifically what you are asking. The FB plans ( download free from the Forno Bravo Store) have a recipe for home made hi temp mortar: 3:1:1:1 sand, portland cement, fireclay, lime. It has been used by many of the builders on this site, some people have modified it. What I have been able to learn from reading is that lime makes the mix easier to work with, the cement burns out in the curing process and that some people feel that a higher ratio of fireclay will result in a better end result.

Good luck, please post what you finally end up using and how it works for you

Eric
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Old 12-01-2009, 01:16 PM
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Default Re: mortar question

The 3:1:1:1 proportion is pretty standard, and the lime really helps. It's speculated that the lime takes over when the portland fails from heat cycling. It also helps to get the finest sieved sand you can get, it makes for a much more workable mortar.
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Old 12-01-2009, 01:58 PM
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Thumbs up Re: mortar question

Paul,
The poor man's mortar is a good, tried and proven, cheap mortar to use. Dmun is right on with his reply, the less portland you use the better. My oven was built using the 3:1:1:1 mix and I would not use anything else, over 2 years down the track, many uses and no cracking! I also used the normal brickie sand and not the finest sieved sand.
I mixed a single batch for my initial soldier course, and it went and lasted for 3 courses, so it is easy to work. The fireclay makes it a lot stickier which is good once you get into the top courses.

Neill
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Old 12-03-2009, 08:29 AM
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Default Re: mortar question

Hi Paul,
I feel a need to chime in about the homebrew mortar mix. I had a chance to use the high-end Refmix (loved it) then finish the last 3rd of my oven with home brew:

FIRST: In spite of a very small flurry of slight changes to the mix lately, the 3:1:1:1 (sand is 3 parts) mix IS THE WAY TO GO. It really works. The 'official' FB down-loadable plan calls for it in this ratio, always has.

SECOND: If you go to dedicated brick yard for any supplies, I strongly suggest picking up your sand there and asking for #90 (90 mesh) silica sand. It's extremely fine grit silica. Not at all like the stuff you get at Home Depot.

THIRD: Having used this homebrew with the fine #90 sand, I can attest to how smooth and sticky it was and that it held my bricks as good as the purchased stuff.

Just like you, I learned a lot from Alan Scotts book but after finding this forum, I've now got a Pompeii pizza oven that bakes bread too and have had a great time building it.

Good luck on your build, Dino
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Old 12-03-2009, 09:59 AM
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Default Re: mortar question

Not being an expert, I must concur on the sand grit. I have only used homebrew (not quite 3:1:1:1, but that isn't my point in this post anyway). I used #30 clean white silica sand from HD. At #30 it does make a pretty gritty mortar, enough so that I find really tight mortar joints a bit difficult to smooth out. Go for a higher grit, at least #50. Dino's recommendation of #90 must make mortar like toothpaste!
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Old 12-12-2009, 08:13 PM
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Default Re: mortar question

I am in South Florida. Because of the high rate of evaporation, I cut the portland to 1/2 and increased the lime to 1and 1/2 in the sandard 3-1-1-1 recipe. I am a firm believer in lime, and the sparing use of portland cement.
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Old 12-13-2009, 04:29 PM
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Default Re: mortar question

“The bread builders by Daniel Wing & Alan Scott”

A good book but do not put the insulation layer under the structural slab. Put the insulation layer between the structural slab and the hearth bricks.
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Old 12-13-2009, 04:31 PM
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Default Re: mortar question

"I am a firm believer in lime, and the sparing use of portland cement."

I agree with Mark. The portland cement only helps with workability and the initial set up. Over time, and with the temperatures reached, the portland cement breaks down.
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Old 12-13-2009, 04:46 PM
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Default Re: mortar question

I think of portland cement as a reagent or catalyst for lime. The other authorities I have consulted regarding traditional masonry indicate that the mortar mix should be no more than 10% to 16% portland cement.
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