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Can you mix sand into dry bagged type S lime before adding water for plaster?  RSS feed

 
Dave Meesters
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Location: Madison County, NC
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We've been using some lime plaster recently on our slipstraw structures, mostly as a top coat over thicker base layers of earth plaster. All of the "official" resources describe making lime plaster by mixing sand into lime putty. This seems especially appropriate in the UK where lime putty is an available resource. We're in the U.S. and I only have access to supposedly-inferior bagged "Type S" lime. This is what we've been using. Since it's pretty laborious to mix sand into lime putty, I've taken to mixing the powdered lime with the sand (I've worked out the proportions so it yields a good final mix), and THEN adding the water to make the plaster. Much easier. Anyone have any thoughts on this shortcut? Am I making an inferior plaster this way? So far the results have seemed fine, but I don't have much to compare it to.

Dave
 
ties Lahlali
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I'm no expert but I am learned that is is always good to mix the dry stuff first before adding water. Sounds like a sound plan
 
Dave Meesters
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Location: Madison County, NC
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ties Lahlali wrote:I'm no expert but I am learned that is is always good to mix the dry stuff first before adding water. Sounds like a sound plan


Ah, that is good to know! Can I ask where you learned to do that?
 
ties Lahlali
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At the moment I am at the panyaproject.org and over here we often use a low quality type of lime to make plaster. My natural building teacher/guru Lola Byron aka "the queen of cob" always told me: "mix the dry stuff first"

Quess otherwise you might risk getting lumps of one type or the otheror the mix not becoming completely consistent I guess. Must say that we mix everything by hand and don't have cement mixers or the like
 
Bryant RedHawk
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Think of mixing the plaster formula as a cake batter, you always mix the dry ingredients then add the liquid to the dry while stirring.
To carry the analogy along, the reason you do this in baking is to fully mix the dry ingredients so that when the wet ingredients are added you have a more homogenous mix.
Stirring while adding the liquids is to prevent lumps from forming.

When I was doing brick laying with a crew, the guy that mixed the mortar for us, would put two shovels of sand in the mixer then turn it on, he then added the Portland cement then he added more sand, then he put in the lime.
The mixer was turning all this time, blending the "ingredients" once everything for the batch was in and fully blended he would take the hose and start adding the water.
I was watching him one day and with his method it took around 4 minutes for him to have a batch ready for us.
When I asked him why he used that method, his answer was "What do you do when you make a batter for cooking?".

 
Dave Meesters
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Location: Madison County, NC
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Yeah, all of that makes sense to me, which is why I mix my dry lime with my sand before adding water. Why then, I wonder, maybe now just out of curiosity, do ALL of the lime plastering resources ALWAYS (in my experience) tell you to mix your sand into lime putty? I know that in England, the "home" of lime plaster, the putty is the starting material for most people so they have no other choice, but I have found that even in the U.S. folks will tell you to mix your bagged lime into a putty before adding sand. Here is a good example: http://buildsimple.org/resources/See%20How%20to%20Make%20Lime%20Plaster.pdf

Maybe they're just not thinking independently. I guess I'm over-thinking it myself, and should just follow my instincts.
 
Bryant RedHawk
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Location: Vilonia, Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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In my opinion the reason all the books say to mix the sand into lime putty is a matter of ancient convention.
slaked lime was discovered by the Romans, this was always made into putty then sand and aggregate was mixed in to the proper consistency.
It is a great method and will always give you good results.

Today we have better measuring tools and scales and our lime is much more consistent.
You can take the time to whip up a batch of putty from bagged lime and most of the old plasterers I know do but their reasoning is based on how they were taught.
Think of farmers, there are many, many farmers that today, even though the science proves otherwise, still think you have to plow, plow and then plow again before you plant your seeds.
Never mind that this poor practice, is completely wrong, and has led to dependency on artificial fertilizers, herbicides, pesticides and kills all the micro organisms that make dirt soil, they do it because "That's the way my great granddaddy did it, my granddaddy did it and my daddy did it, it's good enough for me!".

I have made plaster both ways and My trowel tells me that there is no difference in the quality, just a time difference for mixing a batch. So, I follow the "work smarter not harder" method.

Try both ways, then give both batches the trowel test, choose the one that works best off your trowel and you can't go wrong.
 
Bill Bradbury
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Location: Richmond, Utah
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Hi Dave,

Slaked lime has more plasticity. That's the only reason for mixing hydrated lime with water first. The finished product is exactly the same either way, but application is a little easier if you slake the lime first. There are several pre-mixed lime plaster products on the market now. I use LimeStrong which is pre-mixed pumice and type s hydrated lime. These mixes are a little better than making your own because the gradations and ratios of aggregates are optimized for your specific application.

All Blessings,
Bill
 
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