A Successful Water-Resistant Earth Plaster in New Zealand

Now, I always say don’t build a free-standing exterior earthbag wall (ie. a garden wall or retaining wall), as they are so hard to plaster naturally and keep waterproof. But every now and again someone proves me wrong. Luke and Kath in New Zealand have created some mud magic here, which just goes to show, you should always take advice from experts with a pinch of salt:)

Luke and Kath’s lovely outside kitchen area.

Luke and Kath have done a stellar earth plastering job here, and used multiple techniques to create a waterproof and natural finish. So yes it can be done, but it takes some know-how and patience. Happily for us they have generously shared their process and photos with me (and now you).
 
“We are in the far north of New Zealand. The climate here is not ideal for earth plaster, hot and dry for three to four months over summer and then usually a couple of months of very wet weather over winter. We are on a hill so the wind can at times be powerful and incessant,” explains Luke.
 
Yes, New Zealand certainly wouldn’t be the first place I’d be itching to stick earth plaster out in the elements. But this funky outdoor kitchen has stood three years so far. How come?

“We applied our first coats of lime/earth plaster, onto an earthbag wall, three years ago, with the help of your course. We did two coats at that time, then burnished the whole lot. It has stood the test of time well. The main issue has been a type of creeping grass which sends its tentacles out and under the earth, popping up under and through the plaster. Areas under the drip line of the roof have also weathered significantly. Portions of the sandbags had become exposed so we decided to redo the whole lot,” Luke told me.

The earthbag wall looking good!

My first comments would be that the plaster in these photos looks exactly how you would want it to if you want to stand a chance of creating a waterproof finish. There are no cracks, as the whole lot has been burnished very well (in this case with the back of a spoon). It takes a bit of practice to get this skill off to a fine art, and Kath and Luke have mastered it. One thing we will want to know of course is what was in that earth plaster mixture? The result is heart-warming because so many of the materials were foraged from the land. This was one of things I wanted to achieve with my earth plaster course. I’m not against people buying ready-made clay plasters, but it’s definitely not necessary. You can create amazing plasters using the ground under your feet, and without buying anything.

The earth plaster here looks exactly how it should.

Here is how Luke and Kath made their water-resistant plaster, but be advised, don’t attempt to just copy this and think it will work. They are using their own soil and clay and sand, so it’s not a standardised commercial product.

“We used the same formula of plaster we devised from experiments before doing the initial coats. 10-15% lime, 20% clay/straw, 2-5% cow manure and the balance of sand. The clay we sourced from the stream at the base of our valley. Our soil is basically sand so once sieved is perfect. The manure is from the cows next door. We used hydrated lime (https://www.graymont.com/en-nz/products/hydrated-lime) and mixed with water first, as cheap lime putty is simply not available here. Once applied, we burnished the whole lot like the first batch, as we found that technique to be highly effective at making the plaster weather resistant.”
 
Animal dung, a bit of good quality lime* and some decent burnishing. This is why this plaster has endured.

Luke hard at work.

Now Luke and Kath want to take the plastering further. This time they’re going to add some layers of linseed oil to the wall too.
 
*Luke and Kath used a high quality hydrated lime instead of lime putty. If you want to understand more about the types of limes out there, read this.

Kath burnishing with a spoon.

Related links
 The Perfect Earth Plaster Course
If you want to create beautiful earth plasters from the ground you stand on, you might be interested in my flagship Perfect Earth Plaster Course. It’s a multimedia course with stacks of explanatory videos, PDFs to take away, and all fully downloadable.
 
https://the-mud-home-courses.teachable.com/p/the-perfect-earth-plaster-course
 
My Free Introduction to Earth Plaster
If you just want a taster of earth plaster, sign up for my free introduction to earth plaster here: https://www.themudhome.com/earthplaster-sign-up.html
 
When is the right time for earthbag?
https://www.themudhome.com/mudbuilding/when-is-the-right-time-for-earthbag

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The final result. Note how the wall is topped with flagstones to protect it from the worst of the rain. Good idea!