Cob: Re: White crystals

[marksaich]

The length of time that the effervescence perpetuates will depend on the
salinity of the sand (which from your reply sounds quite high) probably on
the amount of moisture in the wall and the weather and of course how much
effort you put into cleaning it. I afraid I have no exact details of how
long it will persist but I would have thought you'll be looking at a couple
of seasons to a year.
I haven't had time to look up any potential problems associated with this
but if I get a chance I will and get back to you.
Mark
----- Original Message -----
From: Rosemary Lyndall Wemm <lyndall at neurognostics.com.au>
To: 'marksaich' <marksaich at zoom.co.uk>; <coblist at deatech.com>
Sent: Monday, May 22, 2000 1:38 PM
Subject: RE: White crystals


>
> >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-
>
>