[Cob] Mike .. Dome home

[Shannon Dealy]

On Wed, 15 Jan 2014, Tys Sniffen wrote:

[snip]
> Also I did 6 (!) coats of linseed oil, some over 6 days, some all on one
> day, and I'm not really happy with the result.   It's not hard enough.  4
> legged chairs make dents in it.  maybe I did it wrong, but maybe linseed
> doesn't harden clay floors up as much as one would like.
[snip]

One thing to understand about oiling floors is that it makes the floor 
soft (compared to the dried cob surface) until it has cured completely. 
Unfortunately, it is not easy to tell when each coat cures as the surface 
(which is exposed to the air) cures first, trapping the solvent for the 
rest of the coat in the floor below which then cures much more slowly. 
This gives the appearance that the floor is ready for the next coat.  If 
you put a new coat on while the previous coat hasn't cured completely, 
this further seals the floor, slowing the cure of the previous coat even 
more, and adding additional solvent to get trapped.

I once (accidentally) demonstrated this principle when I heated a floor to 
high temperature in order to speed the cure as I added each new coat
(I was preparing to leave the country for several months and needed to 
finish quickly).  The floor was quite hot (about 105 deg F) and solid when 
I was done.  I then let the floor cool and two to three days later without 
the heat driving off the surface solvent, the solvent trapped in the floor 
had made its way to the surface and resoftened the surface linseed oil.

Ultimately, this floor was not really solid for over a year, though I had 
done six heavy coats in that accelerated process.  Fortunately, this was a 
shop floor, so the dents it got from moving things into it right after the 
floor cooled (when I discovered it was soft again) wasn't a big deal.

Your best bet for quicker cure is: warm temperatures, thinner coats,
lots of air circulation through the room, and full cure between coats.

It might help to put a thin coat of the linseed oil you are going to use 
on a piece of cob similar to your floor mix and let it cure outside for 
a couple weeks or in a hot car.  You can smell this to see what it smells 
like after the solvent is all gone and use it as a reference for what your 
floor would smell like once the solvent is gone.  This should help to 
guage when you can put on the next coat.  You may not want to wait until 
it is completely gone, but this might at least give you a better feel for 
how much solvent is left.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
Phone: (800) 467-5820 |          - Natural Building Instruction -
    or: (541) 929-4089 |                  www.deatech.com