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Re: GSBN: Earth plasters

Couple of things. First of all (laughing), plastering in NZ I think is a tad bit different than dehydrated parts of the world such as where I live. I suspect Andy's part of the world is in the dehydrated category.

But on to what you said about fermenting plaster. I have found that the longer any earth plaster ages the better it seems to get. Especially this applies to those containing some fiber whether it be straw or paper. Even for short periods of time we've had large batches of clay and straw plaster rise like bread dough, quite amazing. The only objectionable thing about longer periods is that there is a definite organic odor that comes with it. Personally it doesn't bother me, but others don't get overly excited about it. To see if I can help those who are sensitive we've started some experimental batches with EM, a product known as Essential Microorganisms to see if it alters the process somewhat.

Anyhow, what I like about the fermented mixes is that the character of the mix changes entirely. It is hard to describe, but it becomes much more pliable, plastic, easy to work and the breakdown of fiber I suspect makes it less susceptible to mold when drying in wetter conditions.

The only down side about adding too much paper for an interior plaster is that you're going to sacrifice thermal mass and since that is an impt ingredient when it comes to the performance of a SB building it would seem we don't want to sacrifice that.

On Oct 10, 2007, at 2:05 PM, Graeme North wrote:

We have found the addition of pulped paper as a fine fibre very very good. Its made either from office paper or newspaper it can be made by throwing 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 use.
It gives a very fine fibre which is enormously beneficial in terms of
increasing strength, and durability of earth plasters. If it ferments a bit even better (all ferment seems to help earth plasters using water that has had a bit of straw left in it for a week or two to start to fizz is good as well) Ð there appears to be some enzymic reaction that takes place between
paper or ferment water and clay that helps workability and durability.

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

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

The amount of paper pulp that can be added can be quite high - we often use up to around 30% or so by volume to plaster , and have made mud bricks with
up to 50% paper pulp  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) or straw, and 1 part paper pulp very tough, very light, easy to work, and looking promising. Very good insulation, and very nice to use as gravity increases remember that there is plenty of evidence that gravity doubles
in strength very thirty years.

As to lime over earth IÕve found it works well so far IF there is good keying and wetting 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 and 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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