Monday, February 6, 2012

Examining My Subsoil Composition

As a homeowner, I keep a list of small, non-critical home improvement projects I should do when money, creativity, and free time coincide (i.e. never).  Last week while I was daydreaming, two of these projects collided in my mind and an idea was formed. 

The first project was an area of my backyard that just begs for a flower bed.  Grass won't grow there during the summer because of excessive shade, so it is pretty much overrun by weeds and some years is just bare earth.  The trouble is that the soil is not great and is full of tree roots, so I'd prefer to build a raised flower bed.  That means money for soil and for the material that retains the soil, ideally in this case something that can be arranged in an organic, curving shape, like stone or brick.

The second project is the removal of all the dirt deposited in our basement/crawlspace during the flood last spring.  The dirt is still sitting there because, frankly I just don't know what to do with it.  For reasons I won't go into, it can't go back where it came from, can't stay where it is, and can't go anywhere else on the property.  (Okay, it can't go anywhere else because it's really awful subsoil that nothing would grow in, except trees, as you'll see in a moment.)

Oh, if only there were some natural, locally available, dirt-cheap material to build raised beds with...oh, if only there were some useful purpose for yucky clay that turns hard as a rock when dry...oh!  Bricks!  We could make bricks!  It would be fun and educational for R, put all that dirt to good use, and probably make for an interesting conversation piece during cook-outs!

It turns out, you need some pretty particular soil composition to make good bricks.  (I'm not aiming for excellence, but it would be nice if they didn't crumble in the first good rain.)  After reading a lot of crazy stuff on the internet, I've accepted that my bricks "should be" at least half sand, by weight.  How much sand is in my soil?  Let's find out.

I filled a jar about 1/3 with the soil, then filled the rest with water, stirred, fished out some gravel chunks that I thought might break the jar, and then shook really hard for one minute.  This is the classic test of soil composition.  As the soil settles out of the water over the course of several hours, it should separate into easily visible layers according to particle size: sand settles first, then silt, then clay.  Like many things I have read about and then confidently tried, I am thoroughly confused after trying it.

I was not at all surprised to find that there was no visible "sand" layer in my jar.  Here's a picture of the jar a few minutes after I mixed it up.  (I was, conincidentally, making R a peanut butter and jelly sandwich.  This was amusing for me and confusing for him.)

Left: Natural Peanut Butter, Right: Subsoil Suspended in Water

Several hours later, I was beginning to wonder if my soil was entirely composed of one particle size (which I assumed to be clay).

Subsoil, several hours later

By the following day, however, I could see an extremely faint separation between the silt and clay layers, too faint even to show up on camera.  The clay (top) layer represented about 10% of the total height of the soil.  What?  What?  So, my subsoil is mostly silt, with a tiny bit of clay?

Sigh.  I'm going to do some more research about this, because I just don't like being wrong.  But for the time being, I may just try making a dang brick with it anyway.

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