Materials
Portland cement (NOT a concrete mix just the cement powder)
Paper fiber (I buy the paper insulation you can get from Lowes. It is
already shredded. You can take newspaper and shred it, soak it, mush it more
but this saves a lot of work).
Bucket of joint compound
Armature materials if needed
Mixture
You have to experiment here to get it to the point it feels like clay. Off
hand I'd say 2 parts paper fiber to 2 parts cement. I then just put in
a handful of joint compound, add water and mix by hand. If it doesn't feel
like clay I add more cement and more joint compound.
You can do 3 parts paper to 1 part cement if you just want bulk and are not
concerned about strength. The higher the paper fiber the longer it will take
to dry.
I just do this in a bucket. I've not tried a large scale mixing because a)
you can get tired out pretty easily and then you are wasting the rest and b) I
don't know if it would dry out too quickly.
IMPORTANT!: Wear a mask and rubber gloves. Cement dust easily goes into the
air and it is not a good idea to breathe it. Also, I wear thin rubber gloves.
I much prefer no gloves as I like to feel my subject but the reality is that
cement will suck all the moisture out of your hands.
I've been asked if one can add sand. I've only tried this once. It makes the
mixture a lot less claylike and takes longer to dry and will slump easier, but
you can do it. The plus side is likely added strength.
Armature
I try to avoid anything that will rust as an armature because I just don't
know if the paper fibers will wick water all the way through the sculpture.
If it does it could cause rust on the armature thus splitting the sculpture.
This may not happen at all. I would say though if using an iron armature to
make sure to seal it with paint before applying the cement. This is probably
a good idea with any type of cement mixture in any case.
My armatures are made from styrofoam, pvc piping and aluminum piping. If it
is a "sqaut" figure, meaning triangular or a column type figure I just use
styrofoam but it won't have the strength necessary for limbs. So for my
Greenman figure I used pvc piping. My gargoyles though have all just been
styrofoam, including the one with wings. The wings were just the blue
styrofoam sheeting you get for siding. The papercrete adds amazing strength.
The Process
Build an armature. Don't be hasty with it. Make sure that it
is to the proportions you want
before applying cement. I've had to do some chiseling because I didn't take
into account the extra width added by the cement and threw a piece out of
proportion. I know it's common sense but I don't always have common sense so
thought I'd give the warning in case there is someone else like me out there.
I coat the armature from the bottom up, when it is completely covered with one
layer I let it set for a day IF it has things like "legs", such as with the
Greenman. I needed the strength there in the legs before I could build up the
"musculature" with more cement. This technique worked great!
Once you can start adding "muscles", and bulking up the figure you pretty
quickly learn if you are adding too much at once so it slumps. Be patient.
My experience with papercrete is that you can add additional layers after a
piece is dry and it holds nicely. I've even gone back months later and done
more work on a piece. I know this isn't conventional wisdom but it works for
me.
Make sure and cover the bottom of the armature as well with cement. You don't
want bugs getting up inside your armature. It is said that carpenter ants
love styrofoam.
How long does it last?
Short answer. I don't know. Papercrete houses have mostly been built in arid
areas. And they advise not sealing the surface of a house too much so it can
breathe... BUT you don't have to worry about that for a sculpture so SEAL
AWAY. I use paint and polyurethane. I have one sculpture that has sat
unsealed for at least one winter. He has minor surface crackling but no
structural damage. I think that my sculptures will last my lifetime, but I
don't know. Still, do any of us know how long our art will last outdoors
anyway? When I sculpt a piece I do try to think about how water might pool
on it and try to make it so water will run off as much as possible. Ice in
crevices can be deadly to cement pieces. But paper fibers give a lot of
strength to a piece. I am always amazed how I can coat a piece of styrofoam
with this mixture and once it is dry I can stand on it with no damage.
Painting/Sealing
For my Greenman piece I used a sponge to paint with. This makes sure the
figure gets well covered. I did an enamel base and then added acrylics for
highlights. I used spray polyurethane but want to try the kind from a can
sometime.
You don't have to paint of course but I still think sealing is a good idea
with polyurethane or something else.