Here is her article- and at the very bottom is a paragraph on mixing
clay commercially in volume
For Love Of Mud
by Keely Meagen
Mud is magic. Mud is fun. Mud can also be quarrelsome. Don't get me
wrong,
I love earth plasters. I want all new straw-bale homes to be wearing
them.
They make the most beautiful walls I have ever seen. The colors are
gorgeous and incredibly varied. The walls feel soft and homey. Earth
plasters can be rustic and undulate with the bales, or create smooth
walls
with even curves and a polished finish. The materials are cheap, easy to
come by, and healthy for the environment. Earth-plastered walls breathe
like living beings, protecting bales from moisture damage by exhaling
moisture instead of locking it inside. Mud is a blast to work with, can
be
extremely durable, and is easy to patch and repair when necessary.
Sometimes earth plastering is so simple it is astonishing. Friends in
Arizona and California have found that the earth beneath their straw
bale
cabins had the perfect proportion of clay and sand. All they had to do
was
add water, one also added a bit of chopped straw, and voila! Beautiful
plasters that didn't crack.
So why do I quarrel with my walls? Well, I don't really (mud is always
right). But I have had several long, drawn-out head-scratching sessions
while questioning my walls ("just why are you doing that?") Working with
mud keeps me on my toes and forever curious.
The simple truth is, mud will never be a standardized material like
cement.
Each batch of dirt is different and has its own personality. Earth
plasters
have a slower drying time and must be built up more slowly than cement.
There are very few people with big machines to spray it on (and even
fewer
who have enough experience to be beyond the experimental stage). If you
want smooth walls that don't reveal the shapes of the bales, you are
probably looking at a lot more labor and time. And then, with each new
batch of dirt, there are the potential surprises. In this country, we
are
only beginning to recover the lost art of earthen plasters.
It used to be different
(Information from this section comes from research conducted by Susan
Barger and was published under the title Investigations Into The
Durability
of Plasters, Part One: Initial Materials Characterizations and
Correlation
With Oral Tradition.)
A hundred years ago in New Mexico, each village had its own location for
the best plaster dirt. Adobes could be made from virtually any earth,
but
the plaster dirt was special and was often carted, if necessary, to the
building sites. Its properties were known and loved, and the techniques
for
working with that particular dirt were passed down from mother to
daughter
in the tradition of the enjarradoras.
Unfortunately, much of that plastering knowledge was lost with the
arrival
of the upstart newcomer, cement. The source sites for the dirt are
remembered by few. Carole Crews, Cornerstones (the folks who restore the
old adobe churches in NM), and others have done a lot of research into
the
old ways. Susan Barger has some fascinating interviews with older folks
who
remember participating in the plastering as kids. She also analyzed old
plaster samples, looking for clues to what makes a durable mix. Ms.
Barger
found the chemical reactions in mud plasters to be so complex that they
had
more questions than answers at the end of the research. Clearly more is
needed. But even if we understand how to work with one particular dirt,
the
fact remains that the soil of Santa Fe is different from the soil in
Oregon. In fact, the dirt under my feet may be completely different from
the dirt 30 yards away.
So What Does This Mean?
First of all, relax. Earth plastering is easy. Once in the mud, many of
us
feel we are remembering information our cells have tucked away for us
long
ago. Getting in the mud helps us access that knowledge. I had a similar
experience in one of Robert Laporte's timber framing workshops. After
struggling with the chisels for days, feeling clumsy and awkward, I
experienced something clicking in, and all of a sudden I was handling
that
chisel like I'd been doing it for years. But we shouldn't have to rely
completely on intuition and memory of past lives! Or whatever it is that
happens in those magical moments. So here are some tips avoiding
potential
problems and keeping the fun in the mud.
First, ask yourself these questions:
How much durability do I want and need? Is it a meditation hut or a
conference center? Do you have ten kids?
How much time do I have? (If you need it finished this week, call the
local
cement stucco crew. Earth plasters take longer. Plan it into your
schedule.
Prioritize the areas that need to be finished first. Prioritize the
exterior if winter is coming on. Interiors can be done in cold weather,
but
there are cautions about plastering in winter.)
How much money can I put into this? If you are on a tight budget, get
your
friends to help you and/or do workshops. The materials are dirt cheap
and
the labor will be free. If it is a big house, consider bringing in an
experienced person to show you the ropes and help you figure out the
mixes.
If you want to hire a crew and want smooth, polished walls, expect to
spend
more than you would for cement stucco. If anyone out there knows how to
make it less expensive, write an article and let us know!
What do I want the finished walls to look like? It takes more labor and
materials to create smooth walls out of lumpy, undulating bale walls. If
you like the natural curves, keep them!
What materials do I feel comfortable using? The mining of materials -
even
dirt - is harmful to the earth. Look first at what is around you, and
what
friends have available on their lands. Try to use materials that have
the
least impact to create the plasters you want and need. We will all make
different compromises-make sure yours feel ok to you. And get creative
if
compromising doesn't work for you. Perhaps you'll discover something
that
will help us all out!
Enough Talking And Thinking... Let's Get Into The Mud!
Start Simple. Use the dirt from digging your foundation. Test simple
mixes
(clay and sand, or clay and straw in varying proportions). If one of
those
does not give you the durability you need, or if they are "fussy" (hard
to
trowel) look at other clays, or start adding amendments one at a time.
Don't assume you must use a particular amendment. I tried for months to
get
flour paste (aka wheat paste) into the mix at a Moab, UT cohousing
community center, thinking I needed it for durability... but even tiny
amounts made it ridiculously difficult to trowel. In the end, we settled
for clay and straw. Really strong, easy to trowel, and didn't dust.
(Thank
you Kaki for pointing out the obvious).
Reject sand and crusher fines from the local gravel yard sometimes have
clay and sand in perfect proportions for plaster. It's worth
investigating.
Make test batches for each layer of plaster. If you need a really
durable
plaster, or you are doing a big house, do a lot of testing. The more
familiar you are with your materials, and the larger you make your test
patches, the fewer the surprises you'll find when plastering the walls
for
real.
Forgo chicken wire. It's labor-intensive, a pain to work with and
prevents
you from working the plasters deep into the bales. Cedar Rose developed
the
idea of using a drywall texture gun to spray a thin clay slip onto the
bales before plastering in order to help the plasters really grab onto
the
straw. It Works. (You can also apply the slip with your hands, but it's
really messy).
I now use the following system: patch holes first by stuffing them with
straw dipped into a clay slip. Let the patches dry. Spray the walls once
with a clay slip, and have others come behind working the scratch coat
in
with their hands before the slip dries. Don't build out the wall at all,
just work that first coat deep into the bales. (The elements of this
system
all came from Cedar Rose.)
On smaller buildings where it doesn't make sense to rent a drywall
texture
gun, I combine the slip and scratch coats by making one sloppy, high
clay-content plaster and mush that directly into the bales. It seems to
bond to the wall almost as well and saves me from going over the wall
twice
by hand. Pits work well for mixing large batches of plaster if you have
a
bunch of people. I think it is faster than using a mixer, and easier to
let
the plasters sit overnight. (Old folks in NM say plaster that sits
overnight is better - easier to work with and makes a more durable
plaster.) To make a pit, put 4 or 5 straw bales together in a square or
circle, and cover with a tarp big enough to go over the edges. Mix it by
stomping around with bare feet. You can then roll the mix by grabbing
the
edge of the tarp and pulling towards you. (This helps get unmixed
materials
off the bottom). If there are only one or two people plastering, or it
is
getting cold outside, a mixer is faster and easier.
Use fresh, clean chopped straw so that you do not introduce mold spores
into your plasters. Chop it quickly with a leaf mulcher (a sort of
stationary weed whacker that shoots chopped straw out the bottom). Sears
has a "leafwhacker plus" for about $110, and it is well worth the price
for
big plastering jobs.
Keying plasters into the previous layer helps create a strong wall.
Things
that will help: wet down the previous layer of plaster before adding a
new
layer, and leave the scratch and brown coats rough (if you use a trowel,
come back with your hand or whisk broom or rake to give it some texture
before it dries.)
To Each Their Own
In Building with Earth, John Norton says:
"It is important to recognize that the technology of earth building is
extremely varied, not only in a technical sense - the soils available,
the
way they can be used, and the functions to which they are applied, but
also
in a social sense - from the user's viewpoint there is a great
variation in
what is regarded as an acceptable standard."
Many Thanks
Mud plasters have come a long way in the last ten years, in part due to
the
significant contributions made by some amazing folks researching
traditional earth plastering methods and developing new systems for
plastering straw bales. My thanks to Bill and Athena Steen, Carole
Crews,
Cedar Rose, and Cornerstones for their dedication to the craft and for
sharing what they have learned. My work has been made easier and more
effective because of their teaching. Special thanks goes to dirtbag
magicians Khaki Hunter and Doni Kiffmeyer for their innovative approach
to
earth building and plastering.
C'mon Y'all, Join Us In The Mud!
- - - - -
A Word About Durability
In the cliff dwellings of the Southwest, there are intact mud plasters
that
have lasted well over 700 years, mostly without maintenance! Earth
plasters
can be extremely durable.
There are different approaches to the durability question. Some say if
you
want plasters to last longer, make them thicker. It's true, that works.
In
the Southwest, vertical earth plasters on exterior surfaces erode an
average of 1 inch every 20 years (per Adobe & Rammed Earth Building
Design
and Construction by Paul Graham McHenry Jr.), so a few inches should
last
decades.
Cedar Rose has found that house design, the plaster mix, and application
techniques (particularly the need to key plasters in to the straw and
any
previous coats) all affect durability. I agree. If you want your
plaster to
last, pay attention to all of these. (This subject is probably an entire
article in itself).
More and more in my work I try to think of durability with
sustainability.
How hard is it going to be to repair? I try to keep my mixes as simple
as
possible, and leave the owners with several buckets of dry mix that can
be
wet down and slapped on a needy wall quickly and easily.
To check a plaster patch for durability, rub it hard with your thumb.
Does
it resist dusting and crumbling? Pinch it hard between thumb and
finger. Is
it hard to smush? Turn a hose on exterior plasters (after they have
dried
thoroughly). Does it eat into the plaster slowly or does it disintegrate
quickly?
These tests will help you determine what will hold up and what won't.
(If
you get blasted with horizontal rain and hail often in your area,
consider
adding lime to the exterior mix or putting a finish coat of lime over
your
plasters).
A Word About Clay
Clay is amazing. There are many different types and according to potter
friends, they run in a spectrum from the bentonites (sticky and
expansive/more prone to cracking) to the kaolinites (not so sticky and
hardly expansive/less prone to cracking). So a soil with 30% bentonite
will
act differently than a soil with 30% kaolin. And there can be several
kinds
of clay present in the same soil.
Bevin Dunn blew my mind when she informed me that the clay particles are
not responsible for clay's sticky nature. The mineral fragments linked
to
the clay are what make it sticky! The ramifications of this tidbit seem
enormous. I just can't figure out where to go with this. Ideas, anyone?
Whoops, What is This?
These are a couple of the major problems I have run across in my work:
Mold. At a recent job we switched clays for the finish coat, put out a
lot
of work in one day to get it on the walls, and the next day we were
surprised to see the wall covered with little white fuzzy spots. We
hoped
they would disappear as the wall dried, but instead they stained the
wall,
leaving the rich color with lots of lighter blotches. Wiping it with a
borax solution or hydrogen peroxide changed the color and the
texture... so
we redid the wall, adding dissolved borax to the plaster. Had it been
summer, when we could have had better ventilation and faster drying,
this
would not have been such a big problem - but that mold was fierce and I
think borax would have been necessary anyway.
Mold spores can come in with the dirt or straw. Use clean chopped straw
and
try changing your dirt if you discover mold. Ventilate well. Adding
borax
or lime to the mix will kill molds. If you develop mold when plaster is
on
a wall, spray it with hydrogen peroxide to kill it before adding new
plasters. Mold can be a significant health problem, especially if it is
of
the black slime variety. (I hear vinegar and lemon juice also work, but
have never tried them.)
Effervescence. [ed note: She means "Efflorescence"] Excess minerals in
dirt can rise to the plaster surface, blotching finish plasters. Use
another clay or wash your clay (Call me for
directions if you have to do this), or learn to enjoy the mottled
affect.
This was a serious headscratcher in Moab, UT and the solution (washing)
was
spirit-inspired, but slowed us down significantly. Some batches of clay
were washed better than others, and consequently we still had problems
with
minerals rising to the surface by the time we reached the finish coat.
You
can tell this might be a problem if a white or yellowy film rises to the
surface after mixing up a clay slip and letting it dry.
Freezing Plasters. Do not let your new plaster freeze when wet, before
or
after it go on the walls, until it cures. If they freeze hard enough
before
curing when on the walls, they will become quite crumbly and need to be
removed. If you don't remove them, you may suffer blowouts on all of the
remaining coats, as the plaster no longer grips whatever it was keyed
into
and can't support the weight of new plasters.
If you must do interior plasters in the winter, do the following first:
Put at least one layer of plaster on the exterior if weather permits or
tarp the walls.
Caulk the windows.
Insulate the ceiling.
Keep the place heated.
Ventilation. When a lot of plaster is drying at once, you must have some
ventilation (all that moisture has to go somewhere), but don't open
windows
over wet plaster. Speed the drying of thick scratch and brown coats by
turning up the heat or pointing a fan at them; it is ok if undercoats
crack
as long as they don't pull away from the wall. But don't point a fan or
heater at finish coats or they may crack severely. Keep an even, warm
temperature once you begin the finish coat. Sections of plaster that
seem
to take longer to dry and change color. Usually this is caused by a
section
of plaster underneath that was not fully dry before the next layer went
on.
Because it is still wet, the plaster on top takes longer to dry, and for
some reason plaster that stays wet for a long time frequently changes
color. This will most likely be a problem over holes that have been
patched
with a lot of plaster. Before you put on your finish coat, make sure
your
walls are bone dry!
Money. This is not a problem that comes from the mud, but it definitely
affects the plastering. Cost overruns are common in building, and funds
may
be tight before the plastering even starts. The more of the labor
provided
by owner/friends and workshops, the cheaper the finishes will be.
If it is a big house, a fancy finish, or must be exceptionally durable,
getting the help of experienced plasterers for developing appropriate
mixes
and troubleshooting can save you time and trouble. The straw bale email
list (go to http://www.crest.org and look in the Discussion Groups area
for
archival and subscription information, or send an email to
strawbale@crest.org) is an excellent and inexpensive way to get answers
to
your questions from folks who have experience, or are willing to take
wild
guesses. (Laughs are guaranteed, the wild guesses are usually admitted
as
such, and there is amazing information and experience shared).
Prioritize what you need. Think about doing the plastering in stages
(some
this summer, some next summer). Get creative and let us know if you find
any ways to speed up the process!
* * * * *
I could go on for years with suggestions and ideas, but these are some
of
the most basic helpful
suggestions I have found from my own work with earth plasters.
Before I finish off, I have to mention two fabulous ideas I have come
across:
Earth Plaster on Drywall. If you use wheat paste in your finish plaster
mix, you can put it right
on drywall. It's quick, easy, and beautiful. Just be sure to use a
gypsum-based (non-synthetic,
non-asbestos) joint compound. I had to scrape our test patches off
drywall
and it was tough. If
you want it even tougher, paint the drywall first with a mix of 10 parts
hydrated or homemade
wheat paste, 1 part fine sand and 1 part clay. Let it dry and don't wet
it
down before you plaster
it. I've sunk 16 penny nails into drywall finished this way without
splitting, chipping or other
damage. It surprised even me! Thanks to Cedar Rose for the adhesion coat
recipe.
Easy Nichos. Troweling nichos into smooth curves with no trowel marks is
near impossible, and can take even experienced plasterers huge chunks
of time. A quick, easy way to get lovely shapes with no trowel marks is
to run a strip of 4 mil plastic along the curved edge (perpendicular to
it). It smooths out those edges in a snap. Thanks to Stephan Bell for
this gem.
* * * * *
Keely Meagan used to run Artisan Earth, a women's roving natural
building
and earth plaster crew, with Alyssa Spencer and Kim Barnhart.
Keely is based in Santa Fe, New Mexico
Charmaine Taylor Publishing
STOREWIDE SALE on Books & Videos
www.dirtcheapbuilder.com
Tel: 1-707-441-1632 PST Eureka, Calif.
Commercial clay production I usually work my plasters in pits (5
strawbales in a circle with tarp over bales. stomp with bare feet and
roll by grabbing tarp and pulling towards you- gets the stuff off the
bottom). With a crew, this is faster than using one mixer alone. But
if its cold, forget it. Use a mixer, or two. I know someone who
planned to spray it on the walls with a pump and he planned to mix it
first in a cement truck. Clay slip is easy. Get steel garbage cans,
fill with water about 1/3 full, add 4or 5 five gallon buckets of dirt,
mix with drill and plaster/paint mixer attachment. Fast, quick, easy.
Keep try to get proportions right so you can add all dirt before you
mix. Sediment sinks to the bottom and is not a problem for straw clay.
You can also do it in a pit. If you plan to spray a clay slip on the
bale walls before plastering (and I stongly recommend it - you get a
way stronger connection with the bales and its easier to plaster)
you'll need to put the slip through a window screen so you can spray it
through a drywall texture gun. Easy, just scoop slip out of pit or
garbage can with five gallon bucket and pour over tilted screen
sitting on top of another pit. I've done enough for a 2800 sq. foot
community center in under 4 hours, by myself. I tend to go with pits,
mix it wet, and let it sit for awhile to dry out. Keely Meagan
--Artisan Earth Roving Natural Plaster Crew
