Help! Soil test result and ground for earthen plaster for earthbag building.

Last year I did a soil test and the result was no layers, just water and one layer of dark soil.  Someone suggested to me to post a picture, but I had already thrown it out.  This year, once again, I did a new soil test because we want to be able to use our dirt for rendering the exterior of an earthbag building we will be building in the spring.  The earthbags themselves will be filled with cinder rock, and it will be a round building of only 12' diameter.  We know that we will have to bring in the sand and purchase straw; however, we were hoping to use our own dirt if possible.  I got the same result as last I did last year, but this time I took a picture.  I believe that it is clay only because of when it rains, some low spots hold water for several hours before sinking in and also the ground cracks when dry.  I have pictures of the ground too.  And then, the ground is very rocky, all sizes little bitty to medium size boulders and a lot of flat rocks, as well.  We do not have cinder rock, but there are several cinder rock quarries around here (North Central AZ).

Can anyone tell me by looking at the picture whether they think we have clayey ground or not?  Thanks in advance!

MA Carey

First off, for what you are wanting to do the correct test is to dig a trench so you can see the horizons in your soil.

The floating portion is not clay but something that is lighter than water (probably a sort of pumice or other super light material).
Clay usually settles to form a top layer over rock, humus, and sand.

You can do a finger test (rub a material between finger tips) to determine particle size, slickness and texture of that floating layer.
I don't know where on planet earth you live since you didn't fill out that part of your profile (please do that so others can offer pertinent advice in the future).

The photo of your land shows cracks on the dry surface, this is an indicator of fine to superfine particles forming the surface layer but the fact that this material floats indicates it is not clay.
It could be some sort of silt but I'm thinking a form of light volcanic material.  To further confuse, the rocks in that wall stack appear to be a form of caliche.

When you dig the trench see if you can take a good (clear) photo and put it up here. I will study it and see if there is a clay layer.

Redhawk

First off, for what you are wanting to do the correct test is to dig a trench so you can see the horizons in your soil.

This dirt was taken from the trench that was dug for the earthbag round building, and came from about 12-15" under the top soil.  There were no layers in the dirt, just tan dirt, all one color, and lots of rocks of pea size to baseball size.  Unfortunately, my husband has finished digging the trench down to 18 or so inches and has put rubble in it, which is large flat rock, baseball size rock, graduated to smaller rock, and finished off with cinder rock that we had purchased last year.  So, I am not able to provide a picture of the sides of the trench.  Anyway, there were no layers of color or different consistency.  The ground was very hard and very rocky and we had been working on the trench for over a week.

You can do a finger test (rub a material between finger tips) to determine particle size, slickness and texture of that floating layer.
I don't know where on planet earth you live since you didn't fill out that part of your profile (please do that so others can offer pertinent advice in the  future).

The dirt is some clumps and powdery when broken up, and dry.  The floating layer is somewhat slimy, with some organic matter such as roots and very small sticks.  I noted that I live in north central AZ.  My profile used to show my location, but I changed that as well as my user ID that is viewed, because of some stalking and harassing issues from someone local that must be on this forum or at least lurks on it.  I will not make that mistake again.  I am 50 miles west of Flagstaff, but our terrain is not at all like Flagstaff.

Last year, after trying the soil test, I went ahead and made some sample bricks with this soil, about 1/3, and coarse sand, about 2/3, and some dry cut grasses from prairie land.  Before forming the bricks, I rolled the test material into a ball in my hand and also a long 8" roll and wrapped it around my wrist, and it did stay formed without breaking.  Once I made the mud patties or bricks, I left to dry in the sun for 3 days and 7 days consecutively, testing at those two different times.  When dropping from waist high on day 3, onto the ground, there was no breakage, but at shoulder high, one corner broke off, approximately an inch.  From over my head drop, the brick broke into 3 pieces.  (Test at waist high and over head high were same brick, test at shoulder high was a different brick.  On day 7, dropping from waist and shoulder high, no breakage on ground, but did break upon contact with a wooden floor of shed, into several pieces from shoulder high.  Drop from over head (I am 5'6" so maybe at 6'6" or so height) another brick crumbled when dropped onto floor, and a different brick broke in half and another couple of small pieces when dropped onto ground.  I don't know if these tests mean anything or not.  The unbroken brick was left out in the weather leaned up against the north side of a shed, but unprotected, and it survived several months.  I forgot about it and my husband finally threw it away.

Bryant has said most of what i think.

I'll add this - A soil dominated by clay does not hold water for hours - it holds water for days. So i think in the direction of volcanic ash/windblown deposit or so. Might be a good thing because that is usually a very fertile base for soil formation. One bad aspect is the risk for wind erosion. How deep did your test go. No soil formation ~ layers are not visable under yust a few circumstances.

The picture with the floating stuff is not that clear - looks to me that i might be lots of organic material.

Bryant is also correct in saying that you should give the location. There are lots of resources on line concerning geology and soil formation. Knowing where helps us to help you.

The trench was dug about 18 inches below the topsoil layer, so probably 24 inches or so below ground, and my test of soil was at approximately 15 inches below topsoil layers, so probably 21 inches below ground level.  The area is near Valle, AZ.

I took a peek at the USDA soil map and zoomed into Valle and the immediate area and took a snapshot.  Is your land on the map? It shows the soil types for that area as:

22—Kopie-Servilleta association, moderately sloping
33—Poley-Tusayan association, gently sloping
35—Quivera very gravelly loam, 0 to 8 percent slopes
40—Servilleta-Tusayan complex, 1 to 8 percent slopes
61—Winona stony loam, 0 to 8 percent slopes
62—Winona-Boysag gravelly loams, 0 to 8 percent slopes

Screen shot of soil map for Valle: https://ibb.co/gPbhM5

Here is an example of the info available for these soil types:

Coconino County Area, Arizona, Central Part

35—Quivera very gravelly loam, 0 to 8 percent slopes

Map Unit Setting

National map unit symbol: 1rsz
Elevation: 5,700 to 6,800 feet
Mean annual precipitation: 12 to 14 inches
Mean annual air temperature: 49 to 54 degrees F
Frost-free period: 130 to 170 days
Farmland classification: Not prime farmland
Map Unit Composition

Quivera and similar soils: 100 percent
Estimates are based on observations, descriptions, and transects of the mapunit.
Description of Quivera

Setting

Landform: Fan terraces
Landform position (two-dimensional): Summit
Landform position (three-dimensional): Tread
Down-slope shape: Linear
Across-slope shape: Convex
Parent material: Alluvium derived from pyroclastic rock
Typical profile

H1 - 0 to 3 inches: very gravelly loam
H2 - 3 to 28 inches: gravelly clay
H3 - 28 to 60 inches: very gravelly loam
Properties and qualities

Slope: 0 to 8 percent
Depth to restrictive feature: More than 80 inches
Natural drainage class: Well drained
Capacity of the most limiting layer to transmit water (Ksat): Moderately low to moderately high (0.06 to 0.20 in/hr)
Depth to water table: More than 80 inches
Frequency of flooding: None
Frequency of ponding: None
Calcium carbonate, maximum in profile: 30 percent
Salinity, maximum in profile: Nonsaline to very slightly saline (0.0 to 2.0 mmhos/cm)
Available water storage in profile: Low (about 5.7 inches)
Interpretive groups

Land capability classification (irrigated): None specified
Land capability classification (nonirrigated): 6e
Hydrologic Soil Group: C
Ecological site: Loamy Upland 10-14" p.z. (Provisional) (R035XA113AZ)
Hydric soil rating: No

We are 6000 feet and we get very little rain and snow, compared to Williams and Flagstaff.  Last year was supposedly a wet year and we received several snowfalls but only equaling maybe 16" in total.  As far as rain goes, it usually goes around us and a good rain for us is probably less than 1/2" and that is during the monsoon season.  According to neighbors who have been here awhile, very few winters have they had no snow at all, but normally the snow is like the rain, it goes around us.  

I would say that we are in either of these two soil areas:
61—Winona stony loam, 0 to 8 percent slopes
62—Winona-Boysag gravelly loams, 0 to 8 percent slopes
, with more likely the #61.  However, we are not quite located on the map in your screen shot.  I went into the website and it is a bit complicated, eg, over my head.  I did copy/paste the #61 soil type into google and came up with a choice of Valle, showing the below information:

Map Unit Composition
Map units consist of 1 or more soil types, commonly referred to as "components".
Component Name Geomorphic Position Area Fraction Component Type Horizon Data
Soil Type 1 Valle stream terraces
alluvial fans / Summit 100% Major Soil Type YES

Note: links to horizon data marked with an * are approximate.

Map Unit Data What is a Map Unit?
Cartographic information about this map unit.
Map Unit Name: Valle gravelly silt loam, 0 to 8 percent slopes
Map Unit Type: Consociation
Map Unit Symbol: 57
Map Unit Area: 2072 acres total in survey area
Raw Map Unit Data
Raw Component Data (All Components)

Map Unit Aggregated Data
Generalized soils information within this map unit.
Farmland Class: Not prime farmland
Available Water Storage (0-100cm): 12.08 cm
Max Flood Freq: None
Drainage Class (Dominant Condition): Well drained
Drainage Class (Wettest Component): Well drained
Hydric Conditions: 0
[Annual] Min. Water Table Depth: n/a
[April-June] Min. Water Table Depth: n/a
Min Bedrock Depth: n/a
Raw Aggregated Map Unit Data

Associated Point Data
Links to any NSSL point data within this map unit.

Since I am only really concerned about the exterior rendering of the earthbag building, I think we will try some samples on the walls to see how they turn out.  Kelly Hart has suggested adding lime, starting at 10% to our mixture.  We plan to use lime plastering over the earthen plaster, probably two coats starting at 1/4", then 1/8", and follow with lime wash.  I do know that I will have to bring sand in from a quarry, but will try our soil in the mix.  Owen Geiger suggested that we make some rendering samples now and see how they weather over the winter and see how different mixture samples hold up.  Since we don't have bags yet, maybe I will just plaster some odd pieces of wood pallet we have around here.  If all goes well with a particular sample, we will go with that recipe.  Otherwise, I guess we will try to find some clay dirt and haul that in when we get sand.  

I have issues w/ setting an AOI on the map on mobile devices and have found setting the area of interest to the county and then zooming in is the easiest way. If I zoom out it looses the soil types, so if you give me a direction vector (N, NE, E, etc) I’ll grab another screenshot of that adjacent area so you’ll have the appropriate map.

setting the area of interest to the county and then zooming in is the easiest way.

I did this and actually got a marked point of our place.  I could see the pond that is northwest of us, approximately 3/4 mile, but when trying to pinpoint the soil, I couldn't do it.  I was probably in the wrong place or misunderstood the instructions.  I also tried on the website using our GPS coordinates, and it also was marked, but no soil info, so I am sure I wasn't going into the right paremeters for getting both my site AND soil type.

Anyway, from your screen shot, I would say the railroad showing is west of Hwy 64, mostly runs parallel with the highway, and we are 2 miles east of hwy 64 and 4 miles south of hwy 180 (Valle junctions both 64 and 180).  I am thinking if your screen shot was moved east and south it would show our area.  The funny thing about this area, it is quite diverse.  We are prairie with no trees, but 1 mile in any given direction there are pinon pine and juniper trees, and we are in a lower spot, with rocky ground, but 1/2 mile from us is extremely rockier, redder dirt, and slightly higher ground, maybe 200 feet or so.

Thank you for your assistance, James.  I appreciate that you take the time researching what I can't figure out.

I read through all the comments, including the geologic profile.  The word LOAM keeps on popping up.  The floating material in your shake test is most likely organic material = loam.  Your area is predominantly sedminentary in nature geologically, and I would venture to guess that pure pumice is not involved, however you may have some volacanic ash showing up in your sedminentary layers.   When you do the shake test, the clay will take a long time to settle on top of the silt.  If it settles out quickly, it's silt.   I imagine that what you have is silt.  And maybe caliche which makes it extra hard.

My own ground in Santa Clara County, California is valley bottom land.  It is mostly a very fine silt that appears to be clay, but it's silt.  I imagine other properties have more clay in their soils than mine.  I do get standing water during rains during the winter, but I think that it's just because I'm bottom land and I get the water accumulation from a lot of different directions.  If it doesn't rain, it will drain in a day.

I took my shake test to a cob oven workshop, and my instructor said... well you can add clay and sand......  However being that the only ratios we talked about was clay, sand and straw.... silt is definitely not part of the equation!  
Clay has particular laminar molecular properties that makes things adhere that silt doesn't have, so maybe you can find plaster material elsewhere.   In our area, apparently there's a quarry that has free "pond fill" that is leftover from their excavation and sand screening that's mostly clay.  You might want to keep tabs on some excavators in your area to see if they have clay they are excavating that they want to dump.

When you do the shake test, the clay will take a long time to settle on top of the silt.  If it settles out quickly, it's silt.   I imagine that what you have is silt.  And maybe caliche which makes it extra hard.

I believe that you are correct, Dado.  We picked up some 1/2" minus cinder rock at a quarry in Williams the other day and inquired about reject sand and about clay for future plastering/rendering.  The sand looked usable, but I am not sure about the clay.  It was orange- brown looking, and looked okay, but I would want to do the shake test before purchasing.  The yard man said that would be fine, but I didn't come prepared with a jar to take some home with me, but the next time we are in Williams, will have a jar in tow.  I have been told that if the soil is poor, I can still use it for rendering if I also mix 10% lime putty in with it and the sand and add straw, or I could use cow manure, which there is plenty around here in free-range country.  Another option is to add wheat flour paste for which I was given instructions.  I am certainly glad I am researching all of my options, but of course, I would prefer to find some good clay.  There is a cow pond not far from where we are, and the soil looks very good, but it is not our property and I do not know who owns it or who owns the free-range cattle.  If I did, I would ask about taking some for testing and adding to our soil if it turns out it is clay.

Thank you very much for your input.