[Cob] Re: linseed oil on floors/cob

[littlehouseantiques at att.net]

-- Original message from Barbara Roemer and Glenn Miller : ---------- 

> We mixed linseed oil into our final coat for the floor because we'd had 
> small cracks in the first two layers. Used about a gallon to 50 gals of 
> floor mix (4:1 clay to sand, with lots of finely screened chopped straw). 
> The floor was down for more than a year before it developed a few hairline 
> cracks in this dry summer. We are just ready to reoil it, and expect most 
> of those cracks to disappear with reoiling. Used regular boiled linseed oil 
> when we could keep the house entirely open, and Bioshield Hard Oil #9 
> thereafter. 
> 

Very helpful point about how long it can take for clay to develop cracks.  
Suspect this is the main problem with doing "tests"; likely no one ever 
ages them for this long and depending on humidty levels etc. it can 
sometimes take even longer than a year for cracks to show up in clay.  
Also helpful to know about the re-oiling process (sounds rather like how 
one takes care of a old natural wood floor to me).   

> Still, I wouldn't recommend cob with oil finish for a horizontal surface
> outside.  The Steens' lime plastered bale or cob benches are almost always
> covered with a porch, and their rainfall is low and confined to one season.

There is at least one bench that is not covered by a roof reported has been standing for 5 or 6 years(?):  

http://www.potkettleblack.com/natbild/canelo_buildings2.html

> Don't know about alum, but the Steens have also experimented with olive oil
> soap rubbed into lime plasters for a beautiful sheen.  

Yes, Olive Oil Soap...I've found some references to its use (specifically when
looking for online Alum/soap recipes) but have failed to turn up any detailed 
instructions for a mix as yet.  Perhaps I can persuade my library to get in a 
copy of the Steens book.  After reading up on making your own soap with olive oil 
and realizing that soap made with olive oil never hardens fully, I more convinced 
than ever that the soap in an Alum/Soap mix is simply being used as an "extender" for the alum "paint" which is likely nothing more than the alum dissovled in water.  

Kathy