Dolomitic vs High Calc

https://www.graymont.com/sites/default/files/pdf/tech/finish_lime_characteristics_1.pdf


High Calc Lime isn't widely available in the US. The closest supplier for me is limework.us. 20 hours drive total. For this reason I'm using dolomitic hydrated type S so far I haven't experienced any popping or de-lamination. Fingers crossed.

Magnesium is considered trash aggregate, I use normal cheaper hydrated masonry lime in scratch brown coats. It occured to me that in finish coats possibly I should decrease the amount of my aggregates by 28% to account for magnesiums presence. Is this thinking correct? Should I be doubling my lime to reach 86% calcium oxide content? and then decreasing aggregate? I realize this would be different for tadelakt. I'm mainly thinking about finish coat and skim layers of marmorino or other venetian styles.
 
Getting High Calc Lime isn't as easy in the colonies as it is in EU or the British Isles. Some might say High Calc Lime is as rare stateside as a good world cup football team in Britain :):):). I'm completely joking. I am just jealous of your ability to get High Calc Lime. Thank you for the welcome.

I'm talking about the mixing of Lime plasters from scratch when using dolomitic lime. That is Lime that is not high calc. It is 47% on avg CaO and 28% MgO. Higher Calc 95% CaO etc is suggested to be used for fresco intonaco or venetian work. This is because of Lime pops and the smoothness of the lime. The magnesium is considered by fresco workers to be trash aggregate. It's filler. It doesnt act as a binding agent in the plaster. In Dolomitic its really acting as an aggregate to increase compressive strength of the plaster to some degree and in a tadelakt setting it aids in the waterproofing by increasing surface tension of the plaster. Calcium in contrast I believe absorbs the water and passes it into the pores. In this capacity the presence of Mg is considered to be positive over a High Calc lime as it may be more waterproof than a traditional High Calc tadelakt. This is not my question.

I can't find anyone asking this basically anywhere on the internet but it occurred to me that if you were using between a 1.25:1 to 1.25: . 4 of marble aggregate for marmorino or 1.25 to 2 for a quartz brown coat, these ratio that are propagated are really talking about 95% CaO lime putty not dolomitic. To achieve an end product closer to say a St. Astiers or Carmeuse one might double the amount of dolomitic lime in a mix in order to offset the presence of Mg and decrease the other amount of aggregate such as sand, marble, talc, mica.
 

PNWalan

New Member
Getting High Calc Lime isn't as easy in the colonies as it is in EU or the British Isles. Some might say High Calc Lime is as rare stateside as a good world cup football team in Britain :):):). I'm completely joking. I am just jealous of your ability to get High Calc Lime. Thank you for the welcome.

I'm talking about the mixing of Lime plasters from scratch when using dolomitic lime. That is Lime that is not high calc. It is 47% on avg CaO and 28% MgO. Higher Calc 95% CaO etc is suggested to be used for fresco intonaco or venetian work. This is because of Lime pops and the smoothness of the lime. The magnesium is considered by fresco workers to be trash aggregate. It's filler. It doesnt act as a binding agent in the plaster. In Dolomitic its really acting as an aggregate to increase compressive strength of the plaster to some degree and in a tadelakt setting it aids in the waterproofing by increasing surface tension of the plaster. Calcium in contrast I believe absorbs the water and passes it into the pores. In this capacity the presence of Mg is considered to be positive over a High Calc lime as it may be more waterproof than a traditional High Calc tadelakt. This is not my question.

I can't find anyone asking this basically anywhere on the internet but it occurred to me that if you were using between a 1.25:1 to 1.25: . 4 of marble aggregate for marmorino or 1.25 to 2 for a quartz brown coat, these ratio that are propagated are really talking about 95% CaO lime putty not dolomitic. To achieve an end product closer to say a St. Astiers or Carmeuse one might double the amount of dolomitic lime in a mix in order to offset the presence of Mg and decrease the other amount of aggregate such as sand, marble, talc, mica.
I'm near Seattle. It's practically impossible to find hydrated lime here. I've called everywhere. Closest I've come is lime marketed for gardens/agriculture.

One shop does have lime for construction - it's the Western Lime brand by graymont. It's a dolomitic lime - which I regretfully found out. On graymont's website the defined dolomitic lime as containing as much as 45% magnesium.

In the book Building with Lime by Stafford White, White is pretty strong about using high calcium lines for plasters and lime washes, because of their ability to carbonate. He talks about dolomitic limes and other poor limes having a propensity to be chalky.

Eventually I would like to do a shower in tadelakt. It's my understanding that it's the soap scum that sits on the surface layer that makes the plaster waterproof. I find it interesting that you say dolomitic limes are preferrable for tadelakt. Do you have any more info on that?
 
"The results evidenced that the capillary suction of the Mg-lime mortars is lower, while their pore volume (evaluated through the measurement of porosity and absorption) is similar to that of CL mortars. This suggests that the pore system of the Mg mortars is coarser than that of the CL mortars, which agrees with the coarser grain of the Mg-lime deduced from its lower water demand. This also indicates that Mg-lime mortars possess a good behavior towards fluids, which can enhance carbonation and thus hardening, while enabling good performance in moisture areas. "

https://link.springer.com/article/10.1617/s11527-009-9488-9#Sec24

http://www.premiermagnesia.com/userdata/userfiles/file/CPG/About section/A Review of Magesium Oxide in Concrete.pdf
 
The presence of Mg and its extended carbonation time over calcium being as long as 100 years should result in a recurring chemical reaction and the formation of Magnesium Stearate. Meaning an even thicker regrowing self healing layer of soap scum. As people shower and splash water which inevitably removes some of the soap scum Calcium stearate teh Mg is also present. This means you have to re apply the waterproofing layer less often.
https://en.wikipedia.org/wiki/Magnesium_stearate
 

tta2

New Member
Well, I guess this is the place where all the people from the US (myself included) come for info on lime plaster. Some of the finest lime plastering in the world is in Italy, and a lot of the putty sold there is dolomitic. You can find high-calc dry hydrate in the US, but I'm not sure it's pressure-hydrated like Type S. I fiddled with some fresh high-calc dry hydrate from Mississippi Lime, and compared it to Type S from my local big-box store (Super Limoid was the brand). I couldn't see/feel any major difference. 90+% of the battle is the skill of the applicator. Main thing with dry hydrate is to be sure it's fresh. If you find a fresh batch somewhere (find a Home Depot with a new shrink-wrapped pallet), get it and mix it to putty in 5 gallon tubs. I have noticed that workability does seem to improve on storing it wet. The cohesiveness of the plaster really improves over that mixed dry and then wetted.

High Magnesium limes seem to carbonate just fine, as long as the lime is fresh. I've made limewash (inadvertently) in the process of rinsing out tubs, and after idly painting it on some bricks lying about it carbonated surprisingly well. Type S (official specification is that it's high magnesium) dry hydrate might have different compressive strength than mortar made from high-calcium or straight-to-putty lime mortars, but for plasters I'm not sure that's an issue.
 
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