Andrew Sul

Yes, lime +pozzolan+aggregate=Roman cement. There was recently an article in the Washington post that explains how researchers are examining the mix design of the ancient Romans:

https://www.washingtonpost.com/news/speaking-of-science/wp/2017/07/04/ancient-romans-made-worlds-most-durable-concrete-we-might-use-it-to-stop-rising-seas/

I don't know about wood ash, you would have to try it and make some test cylinders. I would stick with what has historically worked. If you have a local source of fly ash I think that would be a great choice (unless you are making foamed lightweight concrete). Something to keep in mind though; no matter what kind of pozzolan that you use, the quality of mortar that you end up with will be largely determined by your quality of lime. Yes, adding a pozzolan to a feebly reactive lime will improve the quality of your mortar but pozzolans are not miracle compounds. So you will be somewhat limited by the quality of the lime you use. The higher the quality of reactive lime that you use, the higher the quality of your mortar since the pozzolan will be able to react with more of your lime. When I started making my own quicklime, I noticed a huge improvement in the quality of my test cylinders as opposed to the store bought bagged mason's lime. Until about 100 years ago, it was very common for farmers to make their own lime. They would store it submerged in water in a pit or barrels, so that it would not recarbonate. It actually improves with age when stored like this due to crystal formation. It is not difficult to make lime but it is time consuming and of course, you need a place to do it, and you need a source of calcium carbonate. I always thought it would be a good idea to use zebra mussel shells (which are an invasive species in the midwest) for your calcium source since you can get them for free by the truck load from many municipalities. Then you would be making tabby lime which is as good as, or perhaps more pure, than limestone lime.

https://en.wikipedia.org/wiki/Tabby_concrete

I guess it really depends on how much time you have and how much effort and money that you are willing to commit to your project.

I know this is confusing so here is a nice summary of the different types of limes available to consumers:

https://www.lime.org.uk/community/types-of-lime/types-of-lime.html

A quote from the above source:

Hydrated or ‘bag’ lime
This is the lime generally available in agricultural and builders merchants. It is a non-hydraulic lime produced by slaking Quicklime with a shortfall of water which results in a powder. It is generally considered to be an inferior product to the fat lime putty described above for a number of reasons but primarily because it starts to degrade from the moment it is made and can actually fully carbonate in the bag before use. Widespread use of ‘bag’ lime has given ‘lime’ a poor name because of the instances where it simply has none of its original properties left by the time the end-user works with it, hence it fails, dusts etc. If ‘bag’ lime is the only option, then it should be purchased as fresh as possible and left to soak for two days in clean water. Although the resulting product is chemically the same as ‘fat’ lime putty, it is physically different, in particular it is less ‘sticky’. A cement mix with a shovel of hydrated/bag lime in it is not a lime mortar, in this instance, the lime is simply being used as a plasticiser. It should not be used in pre-1919 buildings!

I would never use bagged lime for tataki. Ryan Chivers is playing russian roulette. Maybe his lime will recarbonate, maybe it won't. The last time I visited my parents, I found some lime test cylinders stored away in the basement. I made them when I was a civil engineering student in the 1980s and sure enough, they had recarbonated and seemed reasonably strong. If you review Simon's particular application, he wants to use lime mortar in a rammed earth wall and/or perhaps urbancrete using a typical type S bagged masons lime. In order for any non-hydraulic lime mortar to recarbonate, it must be exposed to atmosphere so it has access to CO2. Masons who have worked on buildings 100s of years old have reported that although the mortar on the surface (exposed) part of the wall had hardened, the mortar on the interior of the wall had not. That's because the interior part of the wall did not have a source of CO2 to recarbonate. So Simon's choices are to add Portland to his mix and make OPC mortar or add pozzolan to his lime so it becomes hydraulic. Hydraulic limes do not need exposure to the atmosphere to harden. Another option for him would be to use a Natural Hydraulic Lime. I haven't been able to find a source in the US, only europe, so that's why I had to make my own NHL. I sure wish a lime manufacturer would start offering NHL in the States. Maybe the natural building segment of the market is too small for them to bother with it but hopefully that will change with time.

Simon Malik wrote:

I'll look-up lightweight foamed concrete. Can you recommend any DIY resources ?

 

This guy is doing some interesting work with foamed concrete:

http://www.domegaia.com/

His foam generator is a bit expensive but it does work well. I made mine for $0 out of stuff that I scrounged from my scrap pile so if you are on a tight budget, you can just cobble one together.

Roman Cement!!! Yes! Well spotted!!! I got tired of making my own hydraulic lime. It is not difficult, just time consuming. So I decided to cheat by adding pozzolan to big box store limes and I can report that it does work. I was so impressed by the results that I opened a pozzolan mine in Colorado. It's not really a mine so much as a surface deposit. My pozzolan is a natural earth product, volcanic ash, from the San Juan volcanic field and I've made dozens of test cylinders to prove that it's reactive. Along with making Roman cement, I've also made Roman papercrete which turned out to be one of my favorite experiments. And just 3 weeks ago, I made a foam generator to see if I can make foamed Roman cement. I'm going to start selling pozzolan on ebay and I'll be offering free samples for testing to interested parties. My samples will be shipped in the small "if it fits, it ships" US post office boxes flat rate boxes. I'm able to cram just over a pound and a half of ash in that size box. It's enough to make some test cylinders and get some experience with your mix design. Vitruvius specified 1 part lime to 3 parts pozzolan (by volume) for general building and you can experiment with the amount of sand you add for strength (I like 2 parts sharp sand). I haven't launched my website yet but let me know if you want a sample. If you have a local source, you can also use fly ash from a coal power plant and it will also make our dead limes react. It's another good option if you can get past the toxicity issues. The only other drawback for me is that fly ash contains carbon and this corrupts the foam matrix if you are using it for foamed cement, whether it's ordinary foamed cement or foamed Roman cement. At least, that's what I've been reading on the web. I have no direct experience working with power plant fly ash since I have a local source of natural pozzolan.

There is a lot of confusion in the US about working with lime. I think this partially stems from the some of the terminology in the industry. In America, when you walk into a big box builders store (Home Depot, Lowes, etc) you can buy sacks of hydrated lime. These sacks are really meant as plasticisers for portland cement mortar mixes. Masons add it to their mortar mixes because it improves the workability of the mortar creating a "fat" or "buttery" mortar. The lime itself has very little to no cementious properties. It will not act as a binder. If you don't believe me, make some test cylinders. Mix sand and lime together, wait a couple of months and you'll be able to crush your test cylinders with your hand. No strength. However, if you made those cylinders out of hydraulic lime, you would get a very different result. Hydraulic limes set similar to portland cement. So what's the difference? Primarily, it's the temperature at which the lime was burned in the kiln. The limes sold in the US are burned at high temperatures and most of the mineral compounds vitrify and become non reactive. When burned at lower temperatures (around 1700F) the end product is a reactive hydraulic lime. It's easy to make lime in your backyard, I've done it hundreds of times and there are lots of videos on the internet instructing you how to do it. It's the only way that I know of to get hydraulic lime at a reasonable cost. You could import Saint Astiers or LaFarge but they are made in Europe and their kilns are coal fired. Shipping costs are very high so it becomes very expensive, very fast. So just adding BB store lime to your slipform project won't help bind your stones together. There is a way to "cheat". You can add a pozzolan to hydrated lime and it will take a dead, non reactive lime and make it reactive. It will then act as a binder. Building with lime is much more popular in Europe so it would be worth your while to research some of the european standards for lime such as EN459. Some good info here:
http://realfinishes.blogspot.com/2012/11/plaster-coating-series-en-459-12010.html
So basically, by european standards, our limes are feebly hydraulic because they have little cementious properties. You would get a stronger wall by using a sand/clay rammed earth system. Of course, you can always use portland cement in your mortar if your heart is set on stone but lime alone won't do the trick. If your wife insists on using portland cement, at least consider lightweight foamed concrete. It's easy to make and very versatile. Again, more popular in Europe than the States. Good luck.  

Google "foamed concrete" or "aircrete" or "lightweight cellular concrete".  You can make planters in any shape you want and lightweight concrete will float. I've made it, it's pretty strong and you can alter your mix design to change the density to suit your needs.

Chris Dubwize wrote:
If you suffer from low ambient temperatures led will not offer heat! So you may need to supplement.
.

40 Celsius = 104 Farenheit

I doubt he's still around since it's such an old thread. FWIW, I have used hay for cob. All the ranchers in my valley grow hay and I would have to drive 2 hours each way to get straw. A neighbor gave me a bunch of hay bales because they had some mold in them, mostly on the bottoms. I opened the bales and put the moldy parts in the compost heap and used the rest for my cob. All the books tell you not to do this but it worked out fine for me. I did have some sprouting but the sprouts just withered and died as the wall dried out. If I had convenient access to straw, I would have used it but I didn't. I do live in a very dry climate so that helped. It worked out so well that I plan on using spoiled bales again. Just my experience, YMMV...

Randy Richey wrote:Heya,

I am getting ready to build a 16x16 structure in an hybrid fashion.  I am wondering if anyone else has done anything like this before.... and with success!  

Imagine a 'normal' 2x6 stick construction all the way around.  Infill with formaldehyde free fiber glass insulation.  Without any vapor barrier, adding wood lap siding to the exterior.  Then on the inside, a 4" (properly secured to the stick framing) layer of earthen plaster with a final layer of Natural American Clay.

The concept is to have thermal mass on the inside of the insulation to absorb the wood stove heat in the Winter versus burning me out. Also to have R19 insulation but without vapor barrier so that the earthen layer can breath moisture in and out and won't get too trapped (slight worried about the lap siding but I might not caulk it to allow vapor movement.

This room with be connected to a 12x16 room with Hvac.  So any excessive moisture coming inside during the hot humid months of central Virginia will be moved around with fans and removed by a ductless HVAC in the 12x16 room.

So do you all think this will work?

I'm doing something similar to a 1970s ranch remodel that I'm working on. I'm building a pizza oven in the corner of the kitchen along an exterior wall. The wall is 2X4 construction skinned with 3/4IN CDX plywood which was standard construction back then. I took out the FG roll insulation and used it elsewhere in the house. A friend had given me some 2 IN thick sheets (4x8) of foam faced with foil radiant barrier. It's not the sort of stuff that I would buy but it was given to me so I may as well reuse it. The remainder of the wall cavity (3 1/2 wood stud minus 2 IN foam will leave a gap of 1-1/2 that I'm going to fill with clay rich cob for thermal mass. Then I'm going to plaster the wall with roman cement (Lime+pozzolan+sand) for even more mass. The idea is similar to yours; create a thermal mass to absorb the heat from the pizza oven but since I'm retrofitting previous construction, I'm also using some modern materials. The biggest drawback will be the time required to allow the cob to dry but I'm in a very dry climate so it shouldn't be too bad. How are you going to build your 4IN earth plaster wall? Are you going to build it up in layers? Four inches is thick enough to make a rammed earth wall if you had backing on the stud side.

Alan Loy wrote:Perlite and clay slip is used as an insulater in rocket stoves.  Would the say apply if used as an outside insulation layer for a building?

The test cylinders I made were kind of fragile. I don't think it would wear well on the outside of a building without a layer of plaster protecting it. You could always add more clay and get a stronger result. It works well in rocket stoves because it's kept in place, kind of sandwiched between the riser tube and the 55 gallon drum. And in a damp climate, you would probably have to stabilize the clay with Portland cement or lime. Otherwise it would be very weak when wet.