Earth Plaster Without Sand - Is it possible?

[dustinmattison]

I have built an earthbag house in the mountains in Sichuan Province, China. The problem I have with making plaster and cob is that the soil is almost completely clay. And there is no sand to harvest nearby. There is something that looks like sand, it is white and has small stones and pebbles in it as well as a powdering sand looking substance. But the sand looking substance can be smashed with your hands into a fine powder. I have tried using this but I still had cracking in the plaster. The only way I was able to prevent cracking is to add about 3 parts sand for one part soil/clay. I also add a lot of straw.



I purchased sand but I have to carry it on my back up the mountain! This is hard work and after trying it this weekend I decided that the amount of sand I need is significant. I need to find another way.



Can I use something else to replace sand? My ideas include:



1. Sawdust

2. Shredded styrofoam

3. Perlite (but this is expensive so I need to find something similar if this is an option)

4. Some kind of waste shredded plastic

5. Others?



I am looking forward to responses from anyone who has suggestions.



Dustin

[Deleted]

Mostly manure from herbivores is used all around the world.
If you cannot get manure you could chop and crush plant parts
then let rot in water a week or longer.

Sawdust is a second choice.

[dustinmattison]

@karl can manure replace sand?　I think I can use sand for the final coat, but for the rough base coats I don't want to carry so much sand up the mountain. Also, I was thinking I could use the rough rocky/pebble soil for the base coats. Even if it cracks, I could then use a better final coat with added sand or perhaps manure if that will do the job of sand at preventing cracking.

Dustin

[Deleted]

The plant fibers from the manure prevent cracks in two ways.
1. Water can escape faster from the inside and thus there
will be more uniform drying inside and outside.
2. Better connection.


Earth Plastering Guidelines for Finishes
thelaststraw.org/earth-plastering-guidelines-finishes/

Clay Plaster How-To
www.dancingrabbit.org/about-dancing-rabbit-ecovillage/eco-living/building/natural-building/earthen-plaster/

[Donkey]

I use manure, chopped plant fibers (mostly chopped straw) and sometimes cattail fluff.
For the first coat or two, I never add sand, just the fiber. I only really use sand in lime plasters and earth topcoats.

A little cracking on lower coats can be a good thing, it provides a good tooth for the next layer to hold onto. As long as the cracking isn't massive, there will be no problem.

[dustinmattison]

@donkey donkey  and @karl @karl Instead of chopped plant fibers can I use chopped/shredded plastic? That is convenient to buy and they use it instead of straw for making plaster. I have straw but my supply is limited and to try to harvest plant fibers other than straw will take too much time. I have been experimenting with making plaster without sand, but I get big cracks. I don't know if it will help if I add more straw or other fibers. If I need to add more fibers then I definitely will need to buy something like shredded plastic fibers because straw is hard to come by here.

Dustin

[Deleted]

Sand will reduce shrinkage a lot.
Shredded plastic fibers would be better than nothing.

[dustinmattison]

@karl what about sawdust? I am thinking a combination of straw/pp plastic fibers/sawdust. There is also diatomaceous earth deposits I can dig up with a shovel about 200 meters from my site.

Dustin

[Deleted]

Any kind of fiber will help.
You can use sawdust or make a paperslurry from old paper.

Diatomaceous earth is commonly used for plasters.
Diatomaceous earth is a natural pozzolan and thus
can be used with lime to make roman cement.
With diatomaceous earth, clay and lime or cement
one can make a castable refractory or a water resistant plaster.

[patamos]

The more the fibre is shaped as filaments (eg horse manure, chopped straw…) the better its ability to help prevent cracking. Straw shredded to 1" minus works quite well with or without sand. Leaf shredders/mulchers are good for processing a bale down to fines.
Water content is another big factor. The drier you can mix a batch without compromising its workability… the less shrinkage will want to happen.
Thus, the finer the non-filament fibre the better

[shilo]

you can look for the leftover from rice pilling.

[dustinmattison]

@karl and all, I finished the based layer of plaster inside the house. I know want to use Lime and Diatomaceous Earth and some clay to make the final coat. Can anyone give me an idea of how much lime I need to use (the ratio)? It costs about $30 for 50 kg of lime. My room is a circle, 3.5 meters in diameter. Do you think 100 to 200 kgs will be enough?

Is lime a better choice than Kaolin Clay? I want to use something white.

Regarding color, I have iron oxide pigments but they don't look that natural. Does anyone have any suggestions on how to create a natural looking bright pigment, like yellow? If I use diatomaceous earth the color won't be perfectly white because my D-earth is mixed with some clay and dirt.

Or I can just use Lime to paint a final thin coat, without mixing with anything else (perhaps some Potassium Silicate.

Dustin

[Deleted]

A natural yellow pigment is yellow ochre (Fe2O3.H2O).

Mineral paint is usualy made up of organic materials such as quark, hide glue,
starch and cellulose or inorganic materials like water glass and lime
and minerals like clay or stone flour.
For the starch one can take boiled and mashed sticky rice.

Paint made with quark or hide glue needs to be used up fast
as it will start to stink after a few days.

For example
1 kg lime
100g sticky rice
100g mineral pigments
2-3 liters of water

Wallpaper glue would be better than the sticky rice,
a much smaller amount would suffice.

One liter is for about 1.5 to 3 square meter.

Mixing of hydrated lime and diatomaceous earth results in roman cement.
One can add up to three parts diatomaceous earth to one part lime.
Parts of the diatomaceous earth can be replaced with clay.