I've been reading up on roman cement and how superior is was and still is to modern portland cement. They used well aged lime putty, and added what is called pozzolan. It initially was a volcanic ash from near the city of Pozzuoli. They later discovered powdered marble and brick would also work. Modern pozzolans include coal fly ash, silica fume, and rice hull ash. Adding a pozzolan to lime makes it set with water, instead of absorbing CO2 from the air.

The thing is, I don't even know where to get these things, and personally would rather not use coal ash. I thought about firing kitty litter, but most of the things I've read about using brick as a pozzolan mention that its due to the transformation of kaolin into metakaolin during firing, and kitty litter is bentonite, not kaolin.

Hi Otto, we use to do it when preserving historic buildings with lime based mortar, and specifically a type of architecture in the Southeastern United States called Tabby. The historic application was to mine the shell midden piles of the native fishing and shellfish communities. These were typically oysters, some mussles, and animal bones. Put in a pit and burned with WAY too much firewood, the slurry at the bottom would be quick lime. That would be slaked, mixed with sand for mortar or more shells for Tabby. If there are still videos online you can check Fort Fredrica National Park, they would do one or so a year for educational purposes.

There are expensive places to find it St. Astier CO in France (or maybe it was Scotland, I forget), Virginia Lime Works in the US for historically accurate hydraulic lime. We had just as equal success with the hydrated lime bags from the local masonry store and reduced our material cost by over 100%. 

Thanks for the info Vern. I looked up tabby and have been reading up on it for a few hours. It doesn't seem to be hydraulic though, its just regular slaked lime made into concrete with shells as the aggregate. Maybe you read my post as talking about hydrated (slaked) lime, but I'm asking about hydraulic lime: lime based mixtures that require water to set, much like modern portland cement. The Romans used hydraulic lime cements to make massive concrete structures that are still standing thousands of years later, and they didn't even use reinforcement like we do today.

The reason I'm asking is because despite acting like portland cement in many ways, they still maintain the 'breathability' of plain lime mortar/cement/plaster while being much stronger.

Otto - Hydraulic lime is also lime that will set up under water. Is that what your after?  That type of lime is typically higher in magnesium.  Are you slaking your own quick lime?  There are other forms of pozzalon that can be used which are readily available at most Home Depots and Lowes.  Scoria works well as does perlite and vermiculite.  The later two are commonly used in potting soil mixes.  The former is occasionally used here in Arizona as a thermal drag material in 'cast in place' lime or cement walls.

Hey Otto

I admitt i'm most curious what you intend to build with it.


There any many substances with pozzolanic properties.


Some are wasteproducts that are much safer than coal ash and such. Coal ash contains heavy metals that might leach out or are unsafe during processing. To be avoided.

If you have no safe, legal and environmentally sound access to natural pozzolanes you could use ceramic waste products. The following links are a bit heavy to read but you could use the key words and key authors to locate information relevant to you. Are you familiar with google scholar? You could find this kind of publications in the library of technical and/or science colleges/universities.

http://www.ipcsit.com/vol28/025-CoimbatoreConferences-T003.pdf
http://waset.org/publications/9997569/a-review-on-the-usage-of-ceramic-wastes-in-concrete-production
http://www.ijettjournal.org/volume-9/number-6/IJETT-V9P253.pdf

I recommend that you don't use anything with fancy colouring (reds, yellows, greens and blues). Those colors are typically based on heavy metal pigments. For an environmental cleanup project some years ago we found a cement plant liked bathroom ceramics (ceramic toilets, white ceramic tiles to name some) best because they usually contain few heavy metals in Europe. I DO NOT KNOW for sure this is also true in the us. The EPA or industrial associations should have info on that.


If you use the stuff beware of the machinery requirements. Heavy duty crushers to produce the powder are just one thing. Dust prevention another.

Personal safety measures are also an issue, dust masks, cutproof gloves & protective eyewear (ceramic shards are SHARP) etc......

BTW it is a very good idea to use ceramics. They usually end up in a landfill, cost lots of energy to mine, produce and dump. Re-ussing should save a lot of CO2.


So that's my 2cents.

Good luck

Erwin

Hey Otto- Sorry didn't mean to get sidetracked. I should've asked what your'e planning to build! They are different but they are also very similar ( I know NHL 2, 3.5, 5 et al.) Also, US Heritage is now selling a comparative product to Virginia Limeworks. The method I was getting at was that instead of using limestone that they did not have in that area, they were able to burn very large ricks or bonfires over a pit filled with oyster shell middens that would also contain pot-sherds from broken pottery providing the needed clay addition to the lime. That resulting lime putty would stay covered in the pit with water for weeks to months. That quick lime would then be removed and remixed with more oystershells for tabby or river sand for mortar. The chemical reaction from the quick lime when mixed with water ( and sand) would create a chemical reaction that can heat a can as hot as fire (hence the term lime-burn amongst masons) It was definitely hydraulic as they built foundations for sugar mills right at the banks of the rivers so the boats could unload the cane right into the mill. The Coastal Defense Forts in that area were the same.

Are you trying this in a pottery kiln with a crucible or something?

I'll try to dig up some old material I have. I went to school for architectural preservation in the states, france and mexico and taught historic preservation at college. I don't how much made it with us in the move but I should have something from my apprenticeship as well.

Well, I'm not actually building anything at all, just trying to get information. I'm designing my dream home. So far my plan is to do a reverse brick veneer: i.e. conventional framing outside, brick inside. Theoretically however, this would be used as an exterior finish/stucco. I've heard a lot of mixed info about the strength and durability of plain lime putty mortar. I also live in a very hot area, where I would probably have to hose down the lime much too often for it to set properly.

Oh cool, I"m doing the same thing, actually just dug out the foundation for the greenhouse to create a Trombe wall on the south facade of the WellHaus. Trying to make space for the big addition. 

Yea the stucco part is a bit tricky in the heat. In Savannah, GA we had to build irrigation with mist machines on a timer. Sometime I would leave a trough of water on the ground and seal the wall up with plastic and make it a giant humidifier. On smaller projects I could leave wet burlap over it and mist the burlap. You know though, those were full masonry brick walls over 24" thick so they would absorb alot of the moisture through wicking.

I've also stuccoed additions to match the existing but used portland mix. Are you looking to stay away from it? When I was an apprentice I remember coming home and when I went to take a sip of beer all my knuckles were bleeding because they were so burned up, had to sleep in gloves full of neosporane.

Weel, GOOD LUCK! I hope I didn't confuse, I always digress, ADD

Otto - I live in Baja Arizona - gets pretty hot here.  Yet the history of lime plaster goes back many hundreds of years here.  The San Xavier Mission , just south of Tucson, was built about 350 yeras ago with lime and didn't need repairs until the 1980's.  It's mostly a matter of doing it at the right time of year, using high quality lime, free of mineral contaminants.  Slacking your own from quick lime and leaving it in putty form for as long as you can wait will improve the quality.  The reason Roman projects lasted so long is because they had a law requiring all civil projects to use lime that had been slacked for a minimum of 30 years.  The lime Michealangelo used in the Cistin Chapel had been slacked for 60 years.  You can also add a hydrophillic or structured water material like nopal juice to the mix which will help it to hold water longer, which will allow it to recarbonate (set up) more slowly.  The latter was used on the San Xavier MIssion.

Hey Otto et all, I too am very interested inhydraulic lime. I am also in Arizona, NE area, and i have a strawbale house that currently is rendered with earth, but it is way too labor intensive to maintain in our wind driven rains-- that blast the SW side of the house. I currently have several buckets of lime puddy from 'builders lime type S' which is a NON-hydraulic lime that I can use in areas that are less blasted by sideways rain. But I am trying to find a source of the low to mid range hydraulic lime to render the most exposed areas (needs to be breathable enough for my strawbales). I did speak to the folks at US heritage group, and they have a 3.5 mix, but they want to sell it already mixed with sand, which translates to very high transport costs. Any ideas for sources of just the hydraulic lime powder by itself?

Lime has been fascinating me for a while now. A finish that instead of deteriorating, keeps on turning into rock!!!

I will also be experimenting with using lime for grouting my sandstone slab floors. I will post anything I discover that works. But first I need to find a source of powder... 😊

If anyone wants to see some pics and info of my place you can go to: www.learningtoliveandlovegodsway.com

Hey Otto et al,

It's been a while since I was on the forum, so hello.

First off, let's just start by saying that an air lime like Type S lime is sufficient for any mortar or lime render that you need to plaster less than 1/2" as long as you give it time to cure. It is recommended to protect from sun and wind for a week or more if you have the ability, and hanging burlap works great. If that is unreasonable, just misting the walls several times a day will still give you great results.

There are many options for pozzolans in order to make your lime hydraulic. The key thing you are looking for is that the pozzolan contains amorphous silica and aluminate particles, hopefully close to 50/50. Trans Minerals offers bagged Natural Hydraulic Lime products (St. Austier) which are pricy, ($40 something a bag), and is shipped all the way from France, but it is a great product. Metakaolin is a great natural choice, but again will depend on our location whether or not you can find it locally. Rice husk ash works great, but good luck finding it in the US. Pumice works as well, and you can find it in the US. Perlite can work, but you want the fines, the waste from the plant operations. Brick dust works awesome, but it's hard to come by. Fly ash works amazingly, but it may contain heavy metals, as does blast furnace slag.

The more hydraulic the lime, the lower the permeability, the higher the strength, and the more brittle it is. Hydraulic lime will almost never be as strong as a cement-based mortar or concrete. But compressive strength doesn't mean it is better. The beauty of lime, especially hydrated lime (aka air lime aka non-hydraulic) is that is is much less brittle and can shift with the building. Concrete is so strong that it buckles upon itself. That is why control joints are necessary when using cement based products, to control where it cracks. Lime is self-healing on a microscopic level due to the free lime moving around inside the carbonated lime. This makes it much more suitable for softer brick, adobe, or any softer material or older building that may shift around.

I guess what I am getting at is unless you plan to use the lime as a foundation, or a thick render, then maybe consider using an air lime like a Type S lime. It has lower embodied energy, higher permeability, and more flexibility. Again, it totally depends on your situation. There is a lot of misinformation out there about lime and it is easy to get misled. Especially if you are getting your information from Europe where they use beautiful aged lime putty and their bagged products are inferior to our ASTM standard products here in the US.

That's more than my 2 cents, but hopefully, it helps. Good luck!

One other thing is that the more hydraulic, the harder that is generally, the harder your materials being cemented together need to be.  Using modern bag mortar with old soft brick or even a soft enough stone will, if exposed to the elements, cause a deterioration  of the softer stone or brick. The softer mortar made from an air cure lime will take the brunt of any expansion & contraction in the wall, while a harder hydraulic mortar will attack the material it's holding in place.