Plaster samples

Two weeks ago, my dad and I worked on some gardening tasks. We had nice weather and the ground dried enough for it to be worked. Gardening tasks are important, and it’s that time of year. My dad has agreed to do a lot of the gardening work in order to free my time for working on the house.

Right now getting the root cellar floor poured and the blocks laid for the walls is what’s standing in the way of significant visual progress on the house. As I’ve been down in the root cellar hole shoveling out dirt that’s washed back in with the rain, I’ve wished greatly that I would’ve been able to have done the concrete and block work last summer. It would’ve saved time right now. I cleaned out about half the washed in dirt a few weeks ago, but you wouldn’t know it now. It actually seems like it’s worse than it was before. I shoveled out a bit last week, but it was frustrating because it was wet and kept sticking to my shovel.

However, as it stuck to my shovel and I complained to no one in particular, it occurred to me that this might actually be a good thing. Why is this dirt sticking so badly? That is one of the properties of clay – it’s sticky. As I continued to grow in height while working in the hole (I had a couple inches of the mucky goo stuck to the bottom of my boots), I became more excited about the possibility that I might be mucking around in the plaster for my straw bale walls.

With this in mind, I collected two samples: one from the bottom of the root cellar hole and another from a pile near the cellar that was excavated from it last spring. I put these samples in jars, added water (and a little salt), shook them vigorously, and left the contents to settle. With this process the larger aggregates and sand settle first, then the silt, and finally the clay (adding salt can help speed up the settling of the clay which can take a long time). Once everything settles, you can determine the relative percentages of the different materials in the soil.

It seems like there is a lot of clay in my samples, so much, in fact, that I cannot clearly determine the lines of demarcation between the different strata. When working with the dirt in my hands, there are clearly some small rocks (aggregate) mixed in, but nothing too bad.

The next thing to do was to try making some sample batches of plaster with this dirt. I brought some up the hill along with a hay bale from the barn. I cut the bale in half with my chainsaw so that I would have twice the surface area to try out my samples of plaster on. Then, I mixed two batches of plaster using dirt from the pile near the cellar.

For the first batch, I mixed on part dirt, one part washed masonry sand, and one part chopped straw (not pressed into the measure, just loose). I plastered a section of the side of the first half bale with this mix. Then, I mixed the second sample using on part dirt, two parts sand, and one part chopped straw. My younguns helped me put this plaster on another part of the same surface as the first plaster.

The plaster actually felt good, and we enjoyed putting it on the bale. The second batch felt a bit sandier, of course. Both went on nicely. They’re not dry yet, though. So, I haven’t determined for sure their suitability for the walls in the house.

The weather’s a bit cool, so it’ll take a little while for them to dry completely. At that point, I’ll see how well the samples adhered to the bales and check them for other desirable qualities. In the following photos, you can see the texture of the samples and the chopped straw in the plaster. The one on the left is the first batch (one-to-one mix) and the one on the right is the second batch (one-to-two dirt/clay ratio).

It will be really neat if we are able to plaster our walls with dirt harvested from our building site. Previously, I figured that I would buy bags of pottery clay for the walls. This new possible method will save some money and will just be better in many other ways. Even so, in order to get the desired wall color inside our home, the final coat on the walls will probably use kaolin clay bought from the pottery supply store.