[Cob] Installing vapor barrier in earthen floor: concerns about moisture wicking into walls

[Dulane]

I have written to you before and I am dealing with a similar problem. Since
I am on a mild hill, mostly the upside of the house is affected, so I know
it is drainage. That being said, this is the wettest year we've experienced
plus coolest summer, in recent history. But with weather changing as it is,
it's hard to know what to prepare for.

I have to mention that adequate roof ventilation is a must. I think it might
be twice what you might expect...if you have an earthen floor in a wet area.


I had a 3-4 in. layer of pea gravel, then 1-2 in. styrofoam and then 4 in.
of very stiff cob (drier and sandier mix) as my base. There was no vapor
barrier under the styrofoam however, so water can seep in. 

I used the base for 2 years. I laid carpets on it to protect it, and I never
noticed a damp area or rotting carpet. I suspect, because it was still able
to breathe.  

Then I sealed over a 3 in. dense damp finish floor with beeswax and linseed
oil. Not only that, but I fed Mayhem food by adding blood meal and wheat
paste and manure. If I did it again in a climate like the pacific NW, I'd
stick closer to mineral and add minimal food sources for the mold. Lime can
be used in a floor mix, and it is antibacterial.
  
If you are worried about the walls, I'd say...just make sure they are
painted with a lime based paint that breathes better than the floor ever
did. Also, I left a floor area behind a shelf unfinished, and there is no
mold there. Maybe some built-in ceramic floor vents would be a pre-building
consideration. You could always stuff them with insulation and cob over them
if they didn't serve their purpose. I have a cooler box vent which is lower
on the wall and it helps circulate air.

I bet cob floors are great in an arid area.

-----Original Message-----
From: coblist-bounces at deatech.com [mailto:coblist-bounces at deatech.com] On
Behalf Of Brian Ziggy
Sent: Wednesday, August 03, 2011 9:38 AM
To: coblist at deatech.com
Subject: [Cob] Installing vapor barrier in earthen floor: concerns about
moisture wicking into walls

Hi there:

I've made the decision to tear out my current earthen floor, which lacks a
vapor barrier and insulation. Here in northeast Missouri, we have extremely
heavy, damp soil, and I've been experiencing a large amount of condensation
and mildew on my floor, possibly from moisture wicking up. Homes with vapor
barriers under earthen floors in this area have done well. I will be
following suit.

I have dug out the entirety of the original floor, exposing the gravel
underneath. The next step is to lay down the (6 mil poly) vapor barrier. I
want to seal it to the urbanite foundation around the perimeter of the
house, but I fear that will send the rising moisture straight into the walls
instead. Is this true? Will we be simply sending our problem elsewhere?

As a note: the foundation is urbanite, on a 18" deep gravel trench. The
foundation is exposed and uninsulated.

Any thoughts about this would be very welcome. Thanks for your time!

- ziggy
www.small-scale.net/yearofmud

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