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

 
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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
 
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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
 
gardener
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Location: Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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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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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.
 
pollinator
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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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I'm learning about lime putty for the home we are building, reading the book "Building with Lime" by Stafford Holmes and Michael Wingate, and watching a lot of videos on the subject.  From what I can tell, there are two main reasons to make the putty first.  One being so the lime has time to hydrate and develop its characteristics.

But the second is that the recipes for plaster are based on volume - but it's the volume of hydrated lime putty to sand - not lime powder to sand.  I think the recipes for mortar, which is what most Type-S lime is used for in the US, are based on dry volume.

We are making our lime putty for interior plaster from Type-S lime.  When you add the water to the lime, it decreases in volume.   It's a lot like adding water to flour in that way, and lime putty is like a dough you make various other things from.  So if you mix dry lime powder with sand using the prescribed ratio for a lime putty and sand -  your quantities of the chemically active material are off.

Now that I think about it, a third reason to make the putty first is that each layer of render and plaster requires a different mixture of the putty, sand, and at some points water or hair/fiber.... so it helps to have the putty all made first, as that's your base.

On top of that, from the info I'm going with, Type-S is a high magnesium lime and requires a specific ratio of sand-to-putty that is different than for high calcium NHL limes.

Before we made our putty for our upcoming building project, I stumbled upon something else that it seems important too -  use really really fresh Type-S lime, or else it doesn't harden up properly.  I learned that in a video by a guy making mortar out of pure Type-S lime in the US.  He figured out that it's freshness made the difference between a crumbly mortar or a rock hard one.  So for our putty, I called around to get a totally fresh batch of the Type-S lime, still on the pallet wrapped in plastic.

I'm suspecting that all these finicky points are why not a lot of people recommend using Type-S lime for plastering nowadays, and why a lot of people have homemade lime plaster attempts fail.  In the US, Type-S seems be used most commonly in mortar, where the cement is relied on for the hardening properties so these treatments don't matter as much.  Here's hoping this works and we don't have a cleanup project instead!

How did your project end up turning out?
 
Dave Meesters
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Location: Madison County, NC
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Hi Kim,
Thanks for the reflections and the information. Yeah, I agree that if you're mixing sand into dry bagged lime, you basically have to work out your own recipe by trial and error. The lime loses SO much volume when you add water. And using recipes that start with putty just won't do, unless you are going to make pure putty and start with that. In my project, a little trial and error yielded a good recipe. It's been a while, but I think I did 3 parts by volume powdered lime and one part playground sand, then added water to make a nice lime top coat.

Bagged type-S lime here comes already hydrated/slaked, so giving it time to develop its characteristics is unnecessary as I understand it.

I second your observation about the freshness of the lime. At one point I made an extra top coat, maybe a pigment coat actually, with the end of a bag of lime that had been sitting around for a while. It didn't cure properly and dusted off of the wall endlessly! A terrible situation. I actually made it worse by coating one part of it with wheatpaste to see if that would hold the dust to the wall, but no, the wheatpaste didn't adhere either and peel off in lime-coated flakes. What a mess!  I finally took a scrub brush to the wall to get off what I could, but it still makes flakes occasionally.   Use fresh lime!  It really matters!
 
Kim Goodwin
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Thank you so much for responding; I was wondering how things turned out.  That's great that they did, and of course wretched on the hard (albeit flaky) lesson learned.  But it sounds like you handled it well!

I have not figured out why the information on how to use Type-S magnesium based plasters is so variable.  I have read all sorts of information - some saying that you can use it instantly, others saying that it has to soak a lot longer than NHL lime in order to work well.

What if all along it comes down to using fresh bags, versus old ones? I found that little gem of info on Youtube, by a guy who had a ton of clips about building computers, and one little video - with barely any views - on his experience making mortar out of just Type-S lime.

The book Building with Lime does have a field test section with instructions to test the reactivity of whatever form of lime you are using.  I guess that's how the professionals do it, which makes sense.  It's not an "experiment" for them and if it flakes off that's a lot of labor they have to redo for free.

This all reminds me of the disturbing observation many have made - that the knowledge for how to survive can be lost in one generation.  Cooking skills are a great common example of that, but almost every skill has been lost now and what was once a basic housing technique used in many parts of the world (meaning plastering in general) may as well be rocket science to most people.

Thanks for sharing your experiences and inspiring others to try, too.
 
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