[Cob] Websoilsurvey

[Mom]

I am so glad someone brought this site up. This is a fantastic  
website, not only when trying to figure out what is the probable clay  
content of your soil (for cobbing) but is an essential resource when  
looking at property (to buy or rent), for building sites and growing  
food. There is all kinds if info for builders (drainage, foundation  
depth below frost line, watertable depth, hardpans, for supporting  
your building structure,etc). They can fairly accurately name the soil  
ok your site, but the thing to remember is that it is accuracy depends  
on how many holes they dug, so yes, things can change a few feet away.  
But anyone building anything, especially a cob structure, should  
really "dig" this site (sorry, couldn't resist).

I agree that it isn't very user friendly, patience is key. There is a  
tutorial, I was just too lazy/impatient to invest the time. The more  
time you spend on it, the better you get at using it, and the more  
valuable it becomes, it is a veritable supermarket of information (it  
also tells you where stone outcroppings are, and if your soil has  
rocks), it is an addictive site.

Also want to weigh in on the clay thing, all clays aren't created  
equal. The white clay mentioned is probably a kaolin (very old  
weathered clay, not much plasticity to it, low shrink swell ratio and  
not good for cob).  The technical definition of clay particle is that  
it is smaller than .002 mm across,  and some clay particles are flat  
(there are names for clay types too). Flat particled clays have great  
plasticity (are very slippery and probably generally better for cob in  
the right ratio) and will have higher shrink swell ratio, which locks  
sand grains together but you will need less of it (or you get too many  
cracks).

To trst fpr clay content amd quality, take a small kneaded lump of  
clay about the size of a shooter marble between thumb and curled  
forefinger and try to extrude or push a ribbon out.  The longer you  
can get it before it breaks the better and higher your clay content is  
(you can look up on web, I can't remember measurements but think two  
inches is a good high clay soil).   Jar test is good but less reliable  
than extrusion methods supposedly, as some clay particles are so small  
that they take forever to settle out. I also agree test bricks are the  
way to go. We made some cob bricks with what I thought was too silty  
of a Western state soil, but they held up amazingly well out in the  
weather after a year (though we didn't get too much rain). Really good  
clay seals out water, which is why certain kinds are used to line  
landfills.

Ok I will shut up now, soil is one of my favorite topics to discuss,  
and hardly anyone in my family wants to talk about it anymore.

Monica



Anyone looking for a good summer read could pick up "Hope, Human and  
Wild", by Bill McKibben on topic of resource conservation, voluntary  
simplicity, "less is more", etc. Example of Curitiba, Brazil, gives  
hope that urban areas can be more sustainable places