mortar question

[shingletown paul]

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 ? 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 fa?ade complete only to find the oven mortar fail. There appears to be a thousand opinions out there should I follow the book?:

[eprante]

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

[dmun]

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.

[nissanneill]

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

[Dino_Pizza]

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

[kebwi]

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!

[markjlabate]

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.

[Neil2]

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.

[Neil2]

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.

[markjlabate]

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.

[Wheels1974]

Re: mortar question

I'm not sure if this will help anyone or whether it will benifit your topic.
I'm far from a expert on building Wood ovens but prior to building our wood oven, I done over 100 hours of research. I have noticed that the vast majority of people when using Vermiculite as a insulation foundation, they mix there Vermiculite with Portland cement. This is very wrong when one is trying to make a layer of insulation mix. If you are using Vermiculite it should be mixed with a refractory cement. If used this way then the Vermiculite works just as well as any product on the market but if the Vermiculite is mixed with Portland Cement then it's defeating the full "INSULATING" purpose.

I have called 6 suppliers here in Australia who sell both Vermiculite, Perlite and various kinds of refractory cement. 5 of the 6 suppliers were adamant about mixing a refractory cement when using Vermiculite/Perlite when making a base for a wood oven due to its insulated purpose.
I would also like to point out when purchasing Vermiculite here in Australia is a more expensive way of doing it. The best way is to use straight refractory cement it's cheaper and very easy to work with as opposed to Vermiculite but BEST of all it's new technology.

The reason I wanted to add this is because im sure some people will write back saying that the suppliers are saying this just to make more profit but that is NOT the case because if they did want to make more profit then they would push to sell the Vermiculite as it is more expensive here in Australia.

P.s. I noticed someone mentioned using REFMIX and loved it. Why don't you ALL just stick with a refractory mortar like REFMIX in the USA. It's simple to work with just add water and off you go. Is there a great deal of difference in price when purchasing REFMIX as opposed to your 3:1:1:1 mix? It would really need to be a sugnificant price difference between the 3:1:1:1 and the REFMIX for you NOT to choose the REFMIX because it's so much easier to work with and as I mentioned above it's new technology. If the 3:1:1:1 mix is half price then I can understand. I'm just curious.

Cheers
Wheels1974

[Tscarborough]

Re: mortar question

Price will vary by region, but here in Texas you can make an insulating layer (4'x5'x4") for less than 40 bucks retail if you buy the ingredients. Homebrew refractory cement will cost about 10 bucks per cubic foot, so it is way more than 50% cheaper to use ready mix, more like 1/5 of the cost.

The downside, of course is that the quality will vary with the skill of the mixer. It is well worth the extra cost for a typical DIY'er to buy the premix, considering the total cost versus the cost of tearing it out and rebuilding it.

This is something I deal with daily, and trust me, it is worth the extra cost for a homeowner to not have to worry about how to do it or why it works, just add water and lay your fire brick.

[Wheels1974]

Re: mortar question

Price will vary by region, but here in Texas you can make an insulating layer (4'x5'x4") for less than 40 bucks retail if you buy the ingredients. Homebrew refractory cement will cost about 10 bucks per cubic foot, so it is way more than 50% cheaper to use ready mix, more like 1/5 of the cost.

The downside, of course is that the quality will vary with the skill of the mixer. It is well worth the extra cost for a typical DIY'er to buy the premix, considering the total cost versus the cost of tearing it out and rebuilding it.

This is something I deal with daily, and trust me, it is worth the extra cost for a homeowner to not have to worry about how to do it or why it works, just add water and lay your fire brick.

WOW that is a huge saving going the homebrew or (3:1:1:1) or what ever is the correct formular. I can understand why people chose this way. I'm just glad our SHERLITE refractory mortar here in OZ is very well priced.

[cynon767]

Re: mortar question

The best way is to use straight refractory cement it's cheaper and very easy to work with as opposed to Vermiculite but BEST of all it's new technology.

The problem is the insulation- straight concrete, whether or not it's refractory, is not insulative. There needs to be something to create airspace. Here in the US, both vermiculite and perlite are relatively inexpensive; mixing them with a binder like cement helps them form a relatively solid subfloor under the hearth. Mixing them with expensive refractory cement might make them a little more temperature-stable, but it would defeat the purpose of using them instead of a more efficient ceramic fiber insulating board... namely, providing a low cost alternative to expensive new materials. They hold up relatively well under compression, and with enough thickness, provide adequate insulation. Really high tech stuff, like castable refractory insulation, is way too cost-prohibitive-- for me, anyway.

If you're willing to spring for the extra cost of refractory materials (as someone else pointed out, somewhere around 5x the price), you might as well use the insulation board instead, and not have to worry about mixing and working with vermicrete or perlicrete.

[markjlabate]

Re: mortar question

I mixed up 12 parts fine vermiculite to 2 parts lime, and 1 part (white) portland, and then went over it with a lime stucco. It seems to work just fine, and it flexes, so cracking is minimal and regular. When the dome cools off, everything seals up.