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Re: GSBN: Earth plasters

Greetings earth plasterheads

I'm catching up with this thread after working away in a dead spot with no
pc/phone access, pure bliss mostly but helpful to realise the usefulness of
the communication age, anyway I digress, In my own experimentation with and
application of earthen renders I have, rightly or wrongly come to some

1. Earth/Clay is very different in different places, one lot dug from
beneath the foundations of the building can be very different fom that dug
from just 50m away.
2. Trial tests on bales with different mixes is a must.
3.When using earthen/clay render I've had kids from 18 months old right
through to 80 year olds all getting stuck in with no goggles, gloves etc
needed, a much different case when using lime where I have to make sure
everyone is fully protected and cannot  let young kids anywhere near! and
the young kids absolutely love it when mums and dads who usually say KEEP
AWAY FROM THE MUD! are suddenly encouraging them to get a load in their
hands and smear it on a wall?

My basic tests are arrived at from various people/sources,
1. Drop test, drop a ball of the mix arm outstretched from shoulder height
to the floor, I like the ball to deform quite a lot but not break into
clumps, if it stays as a round ball then there is too much clay and the
render will crack, if it breaks apart there is not enough clay and the
render will powder off.
2. Smear some of the mix onto my hairy arm, too much clay and I'm picking it
out forever, not enough clay and it powders off when rubbed.
3. Form a small sausage about the size of your little finger then try to
make the ends meet, they should meet maybe with a few small cracks but still
stay intact, if it cracks badly or breaks there is not enough clay, if the
ends meets with no cracking then there is too much clay.
4. Make some different mixes with more or less clay or sand, and try adding
some chopped straw to some of the mixes and apply on some bales, if it stays
stuck when rubbed hard when dry but has cracked badly there is probably too
much clay, if it has no cracks but powders when rubbed hard then there is
too much sand, if it has a few small cracks and stays well attached it's
probably about the right mix which you can then adjust slightly either way
and try again.

I have also mixed earth/clay with lime/sand (in this instance we substituted
half the sand in our 3:1 mix with clay dug from the site) to make a lime
stabilised earthen render for use as a base coat which was some of the best
render I have worked with, very sticky stuff, and this base coat was 'only
just' touch hard when the second coat of straight 3:1 sand/lime was applied
and it had no cracking and almost 4 years later it still looks as good as

I think if you get the mix right with earthen render then it's magical stuff
to work with but without proper testing to get the mix to what I felt was
right I could so easily have ended up using one of the bad test mixes that
would have ultimately meant lots of problems with adhesion or later cracking
and coming away from the wall.

After a couple of pints of Guiness I hope this all makes sense!
plaster on
<a  target="_blank" href="http://www.strawbale-building.co.uk/";>http://www.strawbale-building.co.uk/</a>