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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.
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Signing UpStep 1Tools 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
Trowels.
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
Trowels.
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
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As a suggestion to make your straw bale building greener, save money, and likely save time too:
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.
Mud sticks very well to straw, and lime sticks very well to mud, also protecting and more or less waterproofing it.
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).
Mix with water and a fibre like rice husks or chopped straw from your bales in about 1:4 fibre to mud.
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.
When 100% bone dry, plaster your lime on.
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).
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!
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!
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.
The only ecosystem that actually removes carbon from the atmosphere is oceanic algae, which sinks to the ocean floor.
(Buy your turbines from Europe instead.)
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