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Re: GSBN: Earth plasters

Hello Lars,

I remember from an early mail of you about cellulose fiber that you
stated that too much of this fiber can lead to cracking due to the
swelling of the cellulose. How much paper do you use nowadays? Do you
also use it in outside (earth) finish plaster?



Lars Keller a ?crit :
Paper pulp has been a stable fibre addition to earthen plasters on many
earthen plastered sb-constructions in Denmark the last 5 years.
First it came about by listening to recommendations from ceramists
applauding the reinforced clay.
So when starting to use spraying machines that got clogged up by chopped up
straw and the like paper pulp seemed to be the solution, and it was.
Now we also use it when we plaster by hand, and for example in the
claymortars used to some parts of building Finnish Mass Ovens (Masonry Ovens
in the USofA).


2007/10/11, Graeme North ecodesign@...:

We have found the addition of pulped paper as a fine fibre very very good.
Its made either from office paper or newspaper Ð it can be made by
soaked paper into a concrete mixer with lots of water and just letting it
roll until completely broken up , then draining off excess water before
It gives a very fine fibre which is enormously beneficial in terms of
increasing strength, and durability of earth plasters. If it ferments a
even better (all ferment seems to help earth plasters Ð using water that
had a bit of straw left in it for a week or two to start to fizz is good
well)  Ð there appears to be some enzymic reaction that takes place
paper or ferment water and clay that helps workability and durability.

Paper pulp eliminates dusting from earth plasters Ð helpful especially if
the soil is a bit silty.  It also sticks well Ð we use it over
pre-compressed straw without meshing.
We also use it as a finishing plaster over drywall Ð a very nice finish
it sticks like ...glue.

It is also very effective as an additive to earth bricks as well Ð
robustness, durability, and also lowers density giving better insulation.

The amount of paper pulp that can be added can be quite high  - we often
up to around 30% or so by volume to plaster , and have made mud bricks
up to 50% paper pulp Ð cardboard houses anyone?
I am currently looking at building with cob and mud brick mixes using
roughly 2 parts clay-soil, 2 parts wood shavings (long fibered rippings)
straw, and 1 part paper pulp Ð very tough, very light, easy to work, and
looking promising.  Very good insulation, and very nice to use as gravity
increases Ð remember that there is plenty of evidence that gravity doubles
in strength very thirty years.

As to lime over earth Ð IÕve found it works well so far IF there is good
keying and wetting Ð if the initial earth is a cob type mix with lots of
(straw) fibre with plenty of fibres left hanging out of a rough surface,
then that is good too for tying the layers together.

IÕve just lost a patch off a bit of a small experimental earth plastered
whitewashed straw wall where the earth plasters layers were not keyed well
together. Keying is good.


Graeme North Architects,
49 Matthew Road,
RD1, Warkworth,
New Zealand 0981
Ph/fax +64 (0)9  4259305


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