[Cob] (Cob) termite protection of earth floors

[Barbara Roemer]

We put in an earth floor several years ago, mixing linseed oil into all the
layers, increasingly so for the top, which has made it fairly easy to care
for.  We did not use boric acid in the floor mix, but have used it in light
straw clay walls.  I was adamant about wanting an "earth coupled" floor
without a vapor barrier.  In some way I couldn't then explain, I thought
the earthen floor was more natural in its being part of the cosmos if it
were without a barrier.  We had a deep layer of gravel, well-tamped, before
we laid the floor layers.   I couldn't now tell the difference between an
earthen floor with or without a vapor barrier in terms of some kind of
connection or relationship to the earth.  But, had I to do it again, I
would definitely use a vapor barrier, even over 8-10" of gravel, and I
would use both boric acid and linseed oil in all the coats except the very
top coat for the boric acid (I don't want pulverized boric acid floating in
the interior air).  Even with the deep, compacted gravel bed and all the
linseed oil in the floor mix, we still have moisture moving into the
earthen floor.  It's not problematic - e.g., the floor doesn't feel damp in
winter, but if I leave something plastic sitting on the floor for several
days, white mold appears underneath the item.  The floor is definitely
colder than it needed to be: all that gravel allows cold air to move into
the floor, desirable in summer, but we live in a heating climate.  The air
carries winter moisture and then that moisture condenses whenever anything
plastic remains on the floor (a laundry detergent bottle, for instance) for
more than a couple of days.  Our summers are arid, so it's not a year round
problem.  We have no evidence of termites, although for the first several
years, I had repeated nightmares that the non-pressure treated plates lying
directly on the gravel had been tunneled and the house was being eaten
around us.  We do use BioShield's Hard Oil Number 9 rather than linseed oil
to maintain the floor once or twice per year.  We used linseed oil the
first several years, but it has such a strong odor that it caused headaches
for days, so the Hard Oil has worked well for years.

Barbara in the Sierra Nevada foothills