#11  
Old 03-09-2011, 04:38 PM
Journeyman
 
Join Date: Aug 2010
Location: Glendale, Arizona
Posts: 397
Default Re: Vegas Pompeii getting off the ground

Hi CVCrash,

There are a variety of recipes and opinions on what is best. I'm using:

1 part fire clay
1 part Portland cement
1 part hydrated lime
3 part 120 mesh silica sand. (or 60 mesh or anything in between it and 120)

Recent forum comments suggest an additional amount of sand and also less lime. Some even suggest no lime at all, because it is what starts the hardening process. You can try using less lime if you if you find the mortar sets-up too quickly for your building style. I've tried less lime and more sand but apparently it wasn't enough deviation to notice a difference. These ingredients are fairly forgiving as to proportions.

Mix up small batches of mortar, say one or two, one pound, coffee cans, of dry mix. See how many bricks you can do with that amount and if the mortar thickens too much before you are finished with a few bricks. That routine should give you an idea how much mortar to mix at a time. You may also hear from others about their preferred recipes and mixing methods. Somewhere in the Pompeii directions or on a thread you will find mortar recipes too.

Here is a tip on how to combine the various ingredients for a consistent distribution. Locate a 1/8" to 1/4" screen or a prospectors sieve or a bonsai soil sieve and pour your ingredients through it. It breaks up the lumps and mixes much of the ingredients as they pass through. Work over a 5 gal bucket or large tub. Next you can pour or scoop the nearly mixed dry ingredients a second time into another bucket or tub, use the sieve. This second sifting blends the dry mix consistently. Of course, you can do it the old fashioned way by tossing all the ingredients together and mix, and mix, and mix, etc.

If you decide to mix larger batches of dry ingredients you can do what is called "circle mixing". You will need three five gallon buckets. Toss the dry ingredients into two buckets, don't bother stirring them. A five gallon bucket will hold several recipes of ingredients if scooped with a one pound coffee can. This makes layers of raw ingredients. Pour a partly filled bucket into the empty bucket, then the other partly filled bucket into that one, then pour out half the filled bucket into the two empty ones. Blend this way until all the ingredients are mixed. It seems labor intensive but it works. Wear a dust mask. I like using the sieve method and making small amounts at a time.

The mortar should be mixed smoothly and I have good luck with mortar that is like thick pudding but not as stiff as cold peanut butter. A stiff mix won't let you lay as many bricks before setting up. If it is too thin then it runs off the brick. Somewhere in between is the right mix. Use cool water.

You will find out what hand lotion is all about after awhile too.

Cheers,
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  #12  
Old 03-09-2011, 07:48 PM
GianniFocaccia's Avatar
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Default Re: Vegas Pompeii getting off the ground

Hey Bob!

I thought I read that lime extends the set-up time of portland cement. Do I have it backwards?

John
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  #13  
Old 03-09-2011, 10:08 PM
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Default Re: Vegas Pompeii getting off the ground

Hi John,

I repeated what I read from other forum members about the addition of lime to our oven mortar and took it as reliable. However, I did a Google search on lime, Portland mortar mixes to verify what others were saying. Here is something that might clarify: "The speed of set can be increased by using impure limestones in the kiln, to form a hydraulic lime that will set on contact with water. Such a lime must be stored as a dry powder. Alternatively, a pozzolanic material such as calcined clay or brick dust may be added to the mortar mix. This will have a similar effect of making the mortar set reasonably quickly by reaction with the water in the mortar". Maybe not quite on point but pretty close. Apparently, there are several different types of lime that can be used for various types of mortar. I think any brickie will acknowledge that the addition of a little lime to Portland mortar for common brick construction enhances workability and makes the "mud' sticky. The temperature of the water and its chemical content also affect the mortar set time. There are other forum members who can provide a better explanation.

To contrast with the above, many historic and ancient buildings were constructed with mortar made of lime/sand in various proportions: no Portland at all (It wasn't invented until 1824). I couldn't find anything on the set time or workability of lime mortars.

Cheers,
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  #14  
Old 03-09-2011, 10:15 PM
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Default Re: Vegas Pompeii getting off the ground

Hi John,

Aw, drats. I had a nice long explanation all ready to send but it wouldn't go, then the entire page disappeared. So, here is the short version. Lime adds to the workability and plasticity of Portland mortar. You can add varying amounts of lime but too much will set-off the mortar making it too stiff to use.

Cheers,
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  #15  
Old 03-09-2011, 11:17 PM
GianniFocaccia's Avatar
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Default Re: Vegas Pompeii getting off the ground

Quote:
Lime adds to the workability and plasticity of Portland mortar
Thanks, Bob. This is exactly what I think I've observed. I do notice a stickiness to the mortar that is becoming more beneficial the steeper the courses become. I am curious though, apart from the lime's contribution to the mortar consistency and ease of application, what long-term attributes does it provide? Is it truly a refractory product? As my courses progress (I'm up to the sixth course now) I 've been fudging on the classic 1:3:1:1 homebrew mix: portland/lime percentage (a little less) and fireclay/sand (a little more).

John
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  #16  
Old 03-10-2011, 09:40 AM
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Default Re: Vegas Pompeii getting off the ground

Hi John,

Lime mortar is not a refractory product.

The addition of lime to our oven mortar is only for increasing its workability. Lime can't take the repeated high heat cycles of a refractory oven without breaking down. The amount we use in the mortar is a trade-off. Our ovens don't get much over 1000 deg so it holds up for our purposes.

Look here for information on various lime/cement mortars and their properties.

http://www.lime.org/BLG/Tate_Property.pdf

Cheers,
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Last edited by azpizzanut; 03-10-2011 at 09:40 AM. Reason: corrected spelling
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  #17  
Old 03-13-2011, 11:46 AM
GianniFocaccia's Avatar
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Default Re: Vegas Pompeii getting off the ground

Hey Bob,

Thanks for the link to the paper on Cement-lime mortar. I found it quite interesting that evidence of using lime in mortars dates back to 500 BC. Of particular note was this:

Quote:
Copeland et al (1964) found that if mortar air content is increased from 5% to 20%, a 79% decline in mortar bond strength results.
As a completely self-trained (ignorant?) mason, I have found myself taking a few extra minutes to 'whip up' my homebrew mortar feeling that the extra air-entrainment made the mortar feel more fluffy, and easier to manipulate between bricks when placing. According to the above, this is not such a good idea.

John
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  #18  
Old 03-13-2011, 06:28 PM
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Default Re: Vegas Pompeii getting off the ground

Hi John,

I don't think you have to worry too much about whipping air into the mortar with a trowel and weakening the bond. The type of "air" they were talking about is from an entrainment additive usually mixed in at the cement plant. Portland cements with additives have specs and the bags marked with the type.

The subject of mortar and its variations used for our oven construction is something most newbie's have questions about so hopefully we've helped a little with our discussion and references.

Cheers,
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  #19  
Old 03-13-2011, 08:59 PM
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Default Re: Vegas Pompeii getting off the ground

Hi All,

Here's more on mortar from a fellow forum member that I've pasted here for you.

Quoting from Lars: edited a little.

"I, too, had many questions about mortar.

Originally I got a high test bucket of dark refractory mortar to try out. It didn't seem to adhere to fire bricks very well, and needed to be fired to set. Furthermore, it dissolved when wet the next day.

Then I consulted a potter, actually two of them, who had built many kilns. They BOTH recommended the fire clay, Portland sand lime mix.

Knowing the Portland is just to knit things together and keep the rain from washing away the clay until it gets fired, I decided to put together the 'mix' of different recipes I have seen. I have worked with many different mortars, and the 3:2:1 ( and 1/2) recipe is GREAT --- fine quartz sand, fire clay, Portland, and lime.

The fluffy adherent mixture is twice the fire clay to Portland ratio. The FINE sand is good to keep the small mortar joints ( as possible) and this stuff sticks nicely ( I am up to the 7th chain with no forms.

The clay really retains the moisture a long time, so this allows the P ortland to set up very nicely without getting all the moisture sucked out of the mix.

As I understand it, the mortar is really a space filler, and not necessarily an agent of adhesion. It should get hard ( the fire clay) when fired, and the Portland, ( as I have read) will begin to lose strength on the cool down phase.

I have been cutting all my bricks at an angle so every piece is a wedge. Theoretically it would stand with just spacers in the back, and hopefully the clay will harden and become at least that ( and hopefully more )"

I hope this helps to understand mortar a little better. The recommended mixes are versatile enough that you can adjust the proportions a little to suit your needs.

Cheers,
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  #20  
Old 03-15-2011, 03:26 PM
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Location: las vegas
Posts: 19
Default Re: Vegas Pompeii getting off the ground

thanks for the great mortar advice... i have not been able to find a high heat mortar locally and have purchased 60 grit sand, lime, portland and fireclay.

tomorrow will be a day for the soldier coarse. thinking i will go with the 3:2:1:.5 ratio...
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