This Instructable shows how to work with hydraulic lime plaster on a strawbale building.
Lime Plaster refers to a mortar using only pure lime as a binder and sand as an aggregate.
Lime has a long history of use, serving both functional and decorative purposes.

This is what I'm using as a exterior stucco and interior plaster on this project. I use the St Astier Natural Hydraulic lime and I'm very happy with the result. This is a very old building method, in fact Saint-Astier Natural Hydraulic Lime was used to build the city of Perigueux in France in 30 B.C. I purchased it from PA Limeworks in Allentown, PA.
I used Hydraulic lime plaster because it is one of the "greenest" materials you can use in construction. This is due to its purity, its calcium carbonate composition, it's CO2 absorption, its longevity and potential for allowing the materials to be reused or recycled, and the result of a low energy production process.
Below are some key advantages to using Natural hydraulic lime as a stucco on strawbale .

 Elasticity-Important in minimizing shrinkage and cracking.
Allows for minor movements.If the building moves, a lime mortar will move with the building. Through crystalline bridging, using the free lime content, the lime mortar will heal those cracks that occur. Portland cement can become brittle as a result of it's high burning temperatures

Permeability- Good vapor exchange qualities allow for condensation dispersion.
Allowing structures to breathe reduces or eliminates condensation and rot . Bugs don't like it either.
Hydraulic lime plaster will combine the ability to resist water penetration while allowing the structure to breathe freely

Self healing- small cracks will heal up because of the amount of free lime in the product.
If some cracking occurs in the brown or second coat, you can mist the crack and close it up the next day.

Insulation- The breath-ability of NHL mortars reduces moisture in walls, therefore improving insulation levels.

Reworking- All St Astier mortars can be reworked (8-24 hours), reducing wastage and increasing work rate. This is due to the absence of cement, gypsum, pozzolans or high aluminates.

Recycling- Materials built with hydraulic lime mortars can be reused. the NHL mortar itself may be recycled in a number of ways, such as an aggregate for new lime mortars, fertilizer (NHL is calcium carbonate), or it can be used for water purification to adjust pH levels.

CO2 absorption- The most eco-friendly feature of using limes. CO2 is reabsorbed during the carbonation of the free lime. Also the amount of energy used at the production stage is one half of what is needed to produce cement. Consequently, the release of CO2 into the atmosphere is much less.

Step 1: Tools Needed

These are some of the tools I use to plaster onto strawbale walls. The hawk is basically just a big flat surface to put your plaster on and hold up to the wall. You can make one. The store bought units have a nice thick rubber ring to cushion the weight against your hand. I got mine at a garage sale for a buck

You will need trowels. The finish trowel is the main unit for applying the plaster. It can really move a lot of material quickly.
The pool trowel is the best for smoothing the irregular shapes you encounter in strawbale walls.
Pointing trowels are for getting into tight places. same with the small flat end trowel.
a Hopper sprayer and the compressor to run it, especially for exteriors, if you can afford it it will really speed things up. You will need a compressor that can push 18 CFM's
A cement mixer is essential on a project of this scale. The one I have is a cheapo unit and I'm always having to jerry rig something to keep it working.
For smaller plaster or concrete jobs you can use a drill powered mixer.
Buckets and tarps and rubber gloves.
ladders, scaffolds and other medieval devices.
scratching or scaring tool which can be as simple as a piece of hardware cloth or you can spend 30 bucks on a designer tool.
A big mortar pan is nice when you're up on the scaffold.
A hudson sprayer for misting. Keep it clean and for water only. I got mine for around 18 bucks new.
you might want a set of Coveralls so you don't get plaster everywhere.
Eye protection: if you're like me, if plaster can go in my eye it will, and it burns.
Helpers! sure make things go faster
<p>Excellent job on the shop and on the 'able. I may be trying something much smaller than this in the spring, we have a lot of clay around here, I might try a local clay coating.</p>
Lime is made by heating limestone, which drives out the CO2. The lime won't absorb more CO2 than it had to start with. As a carbon sink, it's a net wash.
My friend that has 20+ years as a concrete techie (yea, there are such geeks) says that making cement is pretty ugly for the environment. As far as this being a 'net wash' on CO2, I would want to see the chemistry behind it to believe anyones claims, either way. Once you have cement/concrete, it is good for hundreds of years if done right, to bad we give most structures less than 50 years to live in this country (USA). The worst thing environmentally in the concrete is the cement. That calcined limestone takes huge amounts of energy to drive off the water. I understand the portland cement industry is one of the highest energy consumers, just in the manufacturing of the portland cement. We use it because it drys/cures so much faster than other kinds of cement. (There is a good article on wikipaedia on cement and portland cement. Cement was used back in the days of Rome, but it did not generate as 'hard' a cement as we have today. Anyway, the article is good reading! I wonder how does the cost Natural Hydraulic Lime Plaster compare to (place your favorite competitor here)?
<em>As far as this being a 'net wash' on CO2, I would want to see the chemistry behind it to believe anyones claims, either way.</em><br/><br/>Nearly everything that people talk about as if they removed carbon from the air actually only store carbon. Growing trees absorb carbon, but rotting trees and leaves emit it. A mature rain forest releases just as much carbon into the air as it absorbs, as does every mature ecology. If the total biomass is constant, there is no net absorption of carbon.<br/><br/>The only ecosystem that actually removes carbon from the atmosphere is oceanic algae, which sinks to the ocean floor.<br/>
Many strawbale building books talk about the net CO2 absorption. Bale and cob houses have been known to be still standing after 500 years. There are still bale houses built in the pioneering days in Nebraska which are still there. If you want references, there are bales web sites that talk about all this. And books GALORE. But the CO2 issue aside, the fact that you are building with sustainable materials, gotten from local sources is huge. HUGE. <br> <br>Great job on the house BTW. I want a stable like this when we live in a permanent home. <br> <br>So no oceanic algas are not the only things that absorb CO2.
Don't forget peat bogs (assuming you don't dig them up)? L
Well, that's the problem, isn't it. (Assuming that you buy into this idea that CO2 is a driver of global warming.) When nature does manage to lock up carbon, we go and dig it up again.
Worse even: people will did a great big hole in a peat-bog, fill it with concrete and mount a wind-turbine on top - "green energy"?! L
Not to mention the resources to make the wind turbine were mined from the rain forest after cutting it down, shipped to America to be refined, sent to China to be made in to the turbine, the sent back to America.
What the hell does this have to do with lime plaster?
<br> (Buy your turbines from Europe instead.)<br> <br> L<br>
Thanks. I don't recall that I claimed that it will absorb more CO2 than it had to start with. The fact that it absorbs as much as it does, when combined with it's other benefits, in my opinion, makes it an excellent building material.
This also has to do with the relatively high insulative properties of your building concept. It's built to last (no wasting energy rebuilding). And provides a lot of thermal mass to hold and reflect heat. That being said having not constructed the building I am assuming a lot of things and am not and expert on the topic.
First let me start by saying regardless of the type of shop your going to have (wood, metal, smelting ect) THIS IS FREAKING NICE!! 2nd, I'm in SC where the temps in summer are usually 3 digits on occasion we have below freezing winters. This question may be irrelevant, however in your notes you stated the ambient temp inside was around 70 degrees. Is that a consistent temp or do you require an additional heat/cooling source? My other question concerns rodents; ie raccoon, mice &amp; rats. Does the lime act as a retardant or did you add something to the straw? I'm a disabled vet &amp; have waited years for a shop of my own. Sadly I know I'll never have one as nice as the one you've built..... but a guy can dream!!! Well done sir. Thank you for your post.
Great instructable!<br>As a suggestion to make your straw bale building greener, save money, and likely save time too:<br><br>You can plaster with mud first to smooth out all the walls and make a great surface to then cover with a thinner and easier plaster.<br>Mud sticks very well to straw, and lime sticks very well to mud, also protecting and more or less waterproofing it.<br><br>Most any dirt that has both clay and sand in it (silt is for gardening, not building!) but ideally you want clay from 10-40% and sand from 40-89/90%. Sand is the strenght (like aggregrate in concrete) and clay binds it together (like cement in concrete).<br>Mix with water and a fibre like rice husks or chopped straw from your bales in about 1:4 fibre to mud.<br>Plaster it on, and it's easy to work, easy to fix, if you make mistakes you can use water to turn it back to mud.<br><br>When 100% bone dry, plaster your lime on.<br>You can do this much thinner because it's being used more like a paint than a plaster, in fact you don't need to add sand for body (this depends how smooth you got your mud undercoat).<br><br>Local mud is a healthier option for the environment (no or little transportation and the only embodied energy is from the food powering your body to dig and mix it!) than anything else, but cheers to you for eschewing cement!<br><br>One other tiny hint - in a historical cob home book, I saw that builders would hang damp burlap sacks around the lime plaster for a week to help it cure slowly. This might save you time and misting!
Codini, I haven't tried this technique/building method yet but I find your instructions very easy to follow. Within 18 mos or so I hope to start my small cabin with outbuildings in north central AR. I'm hoping to incorporate lime plaster either for my workshop or my craft studio. Thanks for sharing your experiences & knowledge.
My understanding is that most Portland cement reaches it's strongest point in around 25-30 years, lime on the other hand binds with CO2 slowly and can take litterally hundreds of years to reach it's strongest point. At that point you have limestone again! The temps that you need to make P.C. are much higher than lime, so embodied energy is much lower with lime, but this stuff is brought over from France, so shipping ads to that. The CO2 issue and even the energy issue is moot after you feel what it is like to be in a lime plastered room. Not to mention the hydrostatic wicking that matches native clay better than P.C. And the St Astier stuff is like working with butter!
Wow that is so cool! I had no idea that plaster could absorb CO2. I loved the look of the plaster on the drywall. Is that the only drywall in your strawbale shop?

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