[Cob] earthen floors

[Shannon Dealy]

On Sun, 18 Nov 2007, Jill Hogan wrote:

[snip]
> Re the floor I just put my linseed oil/turps mixture and the next 
> morning it is fine. Never had areas that don't absorb. Do heat it 
> slightly so it absorbs well. And now my floors are just a treat and 
> copied all over in natural building.
[snip]

How well your floor will absorb linseed oil left puddled on it before 
it skins over will depend on the particulars of your final finish coat,
how well sealed it is from previous coats of linseed oil, and how much 
thinner is in the linseed oil.  A high clay mix is not very porous as is a 
floor with several coats of linseed oil already applied.  Heating the oil 
while it will help with getting good penetration into the floor (not a 
problem with sandier mixes) will make very little difference with 
preventing puddling after the first few minutes in contact with the floor 
at which time the oil will have cooled to floor temperature.  The point is 
you really don't want to count on it absorbing all of the linseed oil 
puddled on the floor because if it doesn't you've got a mess.  If you want 
to understand the problem, just apply linseed oil to a piece of wood, 
don't wipe off the excess and leave it somewhere to dry.  My usual 
approach to application is to allow a puddle of linseed oil to stand 
for no more than 10 minutes in any one area of the floor, and I just keep 
moving the puddle slowly from the far end of the room, back towards the 
door until the floor is completely coated, then leave it to dry, 
preferably with fans running and open windows/doors.

I got a call a couple years ago from someone who had exactly this problem 
with the linseed oil he had applied to an earthen floor and was looking 
for ways to fix it.  The best I could suggest (never having dealt with 
this problem before) was to scrape up the gummy excess and apply thinner 
in the hope it would break down the partially dried remainder allowing it 
to flow into the floor.  I never heard back on how it went.

An additional couple of points worth noting:

    - you will get faster drying and less long term odor from your floor
      with more thin coats and a few days of drying between, then
      you will with a few thick coats.

    - I have heard (second hand) that many people who originally did floors
      using linseed oil mixed with progressively higher levels of thinner
      for each coat have decided the added thinner is unnecessary and
      possibly even counter productive in some ways.  I did my last floor
      without the added thinner and cannot see any benefit to adding it.
      Of course, my floors all have high sand finish coats, if you are
      using more of a clay finish, the thinner may be necessary in order
      to get adequate pentration into the floor since the clay is far less
      porous.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
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