Cob: RE: White crystals

[Rosemary Lyndall Wemm]

>It is almost certainly effervescence. This is the leaching of salt out of
>the wall. It gets in there from the sand (particularly beach sand) and
>sometimes from the water. .....

This area is part of the coastal sand plain. The bore water is full of
minerals which stink and stain everything red [like the colour of my clay
from the hills].  The water I am using is on-line drinking water from the
hill damns so is probably unaffected.  The sand I am using would almost
certainly have come from the local sand plains which are no doubt highly
salty.  So I suspect the culprit is the sand.  As you say, the crystals
brush off very easily .. and then re-occur in the same or another spot the
following day!  I'll keep brushing.  How long does it take to leach out
completely?

The cob wall is now about one foot high and drying out at the bottom.  It's
taken over a week to get this high.  I can't figure out how other people can
do 18 inches a day!  Perhaps their weather is hotter.  It's nearly winter
here.  Or perhaps my mixtures are too wet or too sandy.  The last mixture
has been the best so far.  I changed the clay/sand ratio from 2:5 to 1:2 and
used less water.  I'm still unsure about how much straw to add to the
mixture.  Can anyone supply a rule of thumb.


I've been staightening walls today.  I've discovered that hard cob can be
difficult to shape and firm cob can be a problem when the straw content is
high because the straw comes out leaving holes.  However, the holes are
reasonably easy to fill up with some of the dampish cob which has been
scrapped off.  I'd probably have done better if I'd wet the offending areas,
but I was not in my proper work clothes at the time and didn't want to get
my usual filthy self as I had a doctor's appointment within the hour.
Somehow I don't think it would have gone down too well if I'd arrived
covered in red clay stains!  Oh well, I'm sure the stuff will still be
workable tomorrow so I'll give all the new surfaces a blending "wash" then.


---------------------------------------------------------------------
 Rosemary LYNDALL WEMM,
 B.Mus.(Inst.), T.S.T.C., B.A.(Hons), M.A.(Neuropsych.), etc.  _--_|\
 Clinical Neuro-psychologist                             Perth/      \
 Perth, Western Australia    lyndall at neurognostics.com.au  -->\_.--._/
 ------------------- http://www.neurognostics.com.au ---------------v-