[Cob] Linseed and sunflower oil

[jane at kirstinelund.dk]

According to my teachers in wood carving and the like linseed oil has
special properties. It hardens as it dries which creates a (more or less)
watertight surface. Boiled linseed oil hardens faster, but raw linseed oil
also hardens after some time - how fast and how well depends on the
quality of the oil.

(One problem with buying boiled linseed oil is that it normally contains
rather toxic chemicals to ease the drying. It might be possible to buy
non-toxic boiled linseed oil, though.)

It is possible that cooking other kinds of oil will make them harden too,
but I have never heard of it. And for a floor you definitely need a
hardened surface. From what I have heard getting a good surface on a clay
floor is pretty tricky, and even if sunflower oil works for paint, it
doesn't follow that it works for floors.

It would be an interesting experiment, though.

It wonder what this "danish" tung oil you write about is (I'm danish). We
have something called "tonkin-laque" which is based on linseed oil, and
which is supposed to make a very resistant surface. If tung oil is the
same as tonkin-laque i would suppose that you could make a cob bathtub
with it, though you would probably have to re-laquer it at regular
intervals, and leave it to dry and hardenfor some time before using it
again.

And a warning: From what I have learned you risk spontaneous combustion
with ALL linseed oil, not only boiled. So never leave linseed oil soaked
paper or cloth around. The simplest thing is to burn it right away, or at
least leave it on the stove or fireplace, but if we are talking large
quantities this might not be so environmantal friendly. You can also put
it in water, but then you have to do something with it afterwards.

Jane