Cob floors

[Vernon B. Johnston]

Eric D. Hart wrote on12/7/97 9:08PM my time in Washington (not DC)

>        Exactly how long did you wait for the floor to dry?  How thin was
>your floor 'batter'?  I know somebody in Wisconsin who did an earthen floor
>and it took at least two months to dry (to even be firm enough to walk on
>it).  So I'm curious to know how long it takes and a drying time of less
>than a month would be the best.  I'm thinking it wouldn't be very practical
>to put in  your floor and then build the walls while it dries.  Floors
>always get trashed during construction and I would imagine a curing floor
>would be easily damaged.  So, I guess you have to exterior finishing work
>while the floor is drying.  If you have a detailed work schedule that
>involves an earthen/cob floor I would be interested in seeing it.  Putting
>in the sub floor and then putting up the walls sounds like a good idea.
How
>long does the finish coat take to dry?  Its the thinnest so might only take
>a week or two.

Eric,
    When I put the cob floor in the Sweat/Sauna I did it for several
reasons.  One of the most important reasons was to run a smaller testing for
a smaller area so that I would have some experience with the material before
attempting the cob floor on my bigger home.  This testing is something that
I usually do not do.  My natural inclination is to "go for it".  But... the
"Cobber's Companion" did suggest running at least a square yard test patch
before wading into the larger project.  Perhaps if the person in Wisconsin
had run a test patch, then that 2 months may have been avoided.
    You probably don't know if the earthen floor in Wisconsin was a cob
floor patterned from the "Cobbers Companion"?  Perhaps they applied their
mixture directly on the earth subfloor?  Before I could comment on that
Wisconsin floor I would have to have more detail.
    I can, however, comment on my own floor.  The first layer "batter" I
used is the same as my cob mixture except that it was runnier.  In the book
Michael Smith says, "We like to work with a mix about the consistency of
cake batter".  Due to the cold and rainy days we have here in the Pacific
Northwest at this time of year I use a thicker mix, but not much thicker
than a thick cake batter.  To get an idea of what I am talking about mix up
some cake batter or pancake batter, making it on the thick side, barely able
to pour it out of the pan.  Then... add some straw!  You wont be able to
ball it up.  That's the idea.  Or... just reverse it.  Make up the cake
batter with straw just so you can ball it up, then add just enough  water to
make it pourable.  Anyway... play with it.
    I was able to work on top of my first layer of cob floor within four
days.   The days here at that time were about 55 degrees F with some
occasional wind.  I actually walked on it very carefully after two days.  My
big Black Labrador "Parker" left his paw prints in it, but who cares, this
was only the first layer.  This first layer makes a good working surface.
Any damage caused by construction is going to be covered over by the second
layer of special formula cob which is approximately 3/4 of an inch.  (By the
way, my first layer was 1 and 1/2 inches thick).  And if you choose to put
on the second layer,  who cares what construction damage occurs; it is going
to be covered over by the final 3/4 thick special formula cob.    So you can
see this material is very workable and forgiving.
    Another aspect which is important is the installation of at least a 3
inch layer of drain rock before you start your first layer of cob flooring.
I used 1 1/2 inch drain rock and went a little thicker.  This system is, as
Michael Smith says in the "Companion", a "no vapor barrier" system.  The
drain rock is applied over a  sub-floor (what you dig down to after getting
the top soil out).  If your sub-floor is a bit soft, then tamp it to harden
it up.  Then pour or shovel on your drain rock.  The drain rock acts like a
wick, wicking away any moisture before it can get to the cob floor.  These
rocks probably have a bit to do with the cob floor being able to dry out so
fast.
    Anyway... that is what I did.  All the info is really spelled out nicely
in the "Cobbers Companion", and I do recommend that you buy it.  It will
save you a lot of grief, lot of money, lot of time, and enhance your dreams.
It seems that everyone who has it on this list has recommended it.
http://www.deatech.com/cobcottage/ .
    After the final coat, which I have not applied yet (and I wont until
next year)  then I will consider the oiling and waxing of the floors to make
them hard and water proof.  In the meantime,  I just had my first sweat in
my Cob Sweat/Sauna on this very evening.  And... On the cob floor.
    I hope this helps explain a bit...I appreciate the feedback and
questions.   The building process was fun, and I enjoy this list as well!!!

Vernon vajohnston at nas.com