Since buying some property close to Mt. Shasta lastyear, I’ve been thinking about different ways to use materials I can find on the property to build structures. With the land only containing lava rock, sandy / silty soil with no topsoil or organic matter, and Juniper trees, I was left with only a few options. Based on the condition of the soil, my thinking is that rammed earth may be one of the most promising options.
After researching rammed earth construction and based on the characteristics of the soil, it seems that a mixture of soil, cement, lime, water and possibly an admixture could be combined together into a mix which would have both structural properties and an harmonious aesthetic . The hard part is: What proportion of each do you add to get the best of all these properties?
The soil appears to be made up of primarily sandy rock ash with a fair amount of course silt. It lacks any particles small enough to form clay and pretty much has no cohesive properties. Since rammed earth construction depends on cohesiveness of the soil and compaction, filler or stabilizer must be added. My hope is cement and possibly lime will take care of this and give me a material somewhere between rammed earth and mortar. Now I just need to figure out if it'll work.
Armed with empty Starbucks cups, chop sticks for mixing and plastic eggs as forms, I went about conducting my first tests. Although they need to cure for another couple days to see how they finally come out, here's my results so far:
Mix number 1 consisted of 2-parts sand to 1-part water and cement and mix number 2 consisted of 4-parts sand to 1-part cement and water. Both mixes seem to have gained a considerable amount of cohesion but don't seem to be setting up as hard as I had hoped and appear rather brittle. We'll see if this improves as it cures over the next couple days.
Although I am still waiting on this first round, I am pretty sure the results will be below anything usable. The next step will be to get things ready to do more testing on-site with more mixture combinations - this will include adding lime, possibly a courser aggregate like small gravel, and pounding the mixture into tube forms rather than plastic eggs. We'll see what happens!