[Cob] RE: Oiling Cob

[Bernhard Masterson]

I'd like to put in my two cents after living in my cob house with an oiled floor for the last three years.  I feel living on an oiled cob floor is the best floor experience I have ever had.  Feels slightly springy, and feels wonderful to lay once it is heated by the sun.  Sun bathing in January in Portland, OR is a pretty good deal.  Guests routinely exclaim the most about the beauty of the floor.  And when I practice Tai Qi or Qi Gong I feel more energy from the earth than in any other building.        Using local gravel (sub-floor) sands and clays and then oiling has a far smaller eco-footprint than any other option I can think of including fired clay tile from Mexico, bamboo shipped from Asia, etc.   The processing and transportation is minimal by comparison.     The linseed oil on our floor alone does not make it water proof since there is still some porosity.  An annual beeswax and oil rub creates a surface upon which water beads up on and is easy to clean.  The only oils recommended for applying to floors are those that are oxidizing oils.  Linseed and walnut oils are both oxidizing oils which mean that they "dry".  Boiled linseed oil does have toxic additives to decrease the drying time which is why you will often find raw linseed oil recommended.  Raw linseed oil and walnut oil take much longer to dry.  How long depends on the porosity of the surface to which they are applied and drying conditions.  The more porous the surface the thicker the application and the longer the drying time.  Walnut oil on wood takes about two weeks.   Walnut oil on cob about three weeks.  On my heated cob bench the walnut oil took about one week.  By comparison boiled linseed oil dries in under a week on unheated cob.  Because the porosity of cob is higher than wood you can apply many, perhaps seeming endless, coats that penetrate/soak in.  Less oil is absorbed with each coat provided you have given adequate time to dry.  Two to four coats of oil will suffice depending on how much you thin each coat with solvent.  You can speed the drying of raw linseed oil by first setting it in the sun in a shallow pan for a week.  Cover the pan to keep out dust but allow the moisture to evaporate.      When applying the oil you can eliminate the turpentine by applying hot oil to warm floors or adding a citrus solvent.  The thinner the oil the better the penetration.  Great caution should be used when heating oil to avoid a fire.  And yes when the oil dries there is a smell of paint/rancidity that persists for several weeks.  I did not find it overpowering and feel that several on the list have exaggerated the level of smell or health risk.  After a few weeks it completely disappears.     I have never seen any mildew on any oiled cob that I have built even where condensation from the aluminum frames on my picture windows drips on to the floor.  If there is enough moisture in the cob to mildew, the structure has far greater problems than moldy floors.- Bernhard 
_________________________________bernhard_masterson at hotmail.com
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