All the materials arrived so I started some tests. I did some 10×10 cm test pieces, as well as wrapping a glass bottle. Some early thoughts while the test pieces aren’t even fully hardened yet:

• This shit is messy! No way will I be able to do 5 gram test pieces; at least that much material is stuck to my hands every time I put it on the tulle fabric
• I made some calculations errors. 50 grams of gypsum gets me about 3 pieces of double layer 10×10 cm, not one. This is good. If I want more texture, of course I could use more
• It sets quite slowly, I was still able to put some texture into it about 1½h after mixing. I think even for larger pieces I can just mix a single batch without having to worry too much about the setting time
• I think my fabric is not ideal. The tulle is a tad too “open”, it doesn’t absorb the gypsum material as nicely as the gossamer used by the guy in this video. Still, that doesn’t seem to matter so much – it spreads out easily after applying the layer
• I’m not sure yet how much top layer I will need. The texture of the tulle fabric comes through in spots where I don’t have much material on it, I don’t know how bad that would look when it’s set. Perhaps it’s fine after wet brushing
• Colour:
  • The gypsum plaster material is not pure white, it’s actually a nice beige even if I don’t add pigment
  • The brown is great. Mixed at 4% it gives a warm light brown colour, at 8% it’s not much darker though
  • The black pigment is not as powerful as I had hoped. Mixed at 4% it gives a light cold-ish grey. Also, a little granular – doesn’t mix as easily as the brown
  • It is possible to put a pigmented layer directly onto an unpigmented one, and unless the first layer was very thick it won’t mix through much. This saves some pigment
  • I haven’t tried painting yet. With how the pigments are working, I think I should aim for a nice light brown base colour, wet brushing with a dark colour and perhaps some dry brushed highlights
• Thinking of how to use this material for our festival decorations:
  • The original idea is to make trees. Depending on how strong it hardens, I think it will work!
  • Perhaps we can also use it to make 2D mascots, which we currently saw out of thin plywood. This material is easier to do indoors (no loud/dusty sawing)
  • 3D mascots and objects other than trees could be possible too!
  • If it’s strong enough with thin layers that still let through light – perhaps make a really cool lamp shade?

Next up:

• Testing colour
  • Getting the main colour right: testing a few different percentages of brown, as well as mixing in some black with the brown
  • Getting some brushes
  • Trying some diy dark paint/paste out of the black pigment
  • Wet brushing dark (shadows)
  • Dry brushing light (highlights), e.g. with corn starch
  • Perhaps adding some green flocking powder or some other way to simulate moss
  • For fun: trying my blue and red pigment powders
• Testing texture
  • How thick should the second layer be?
  • Wet on wet, or second layer onto dried first layer?
  • Different techniques of applying bark texture
• Testing construction / backing
  • Different backing materials (paper towel, paper, cardboard, plastic..): how strong is it?
  • Trying 3D shapes: how strong is it?
  • Vaseline to go backing-less?
  • Making “hinges” for folding tree design

To be continued.

Found this video, I think he’s a theatre decor making teacher. He uses gossamer fabric drenched in drywall joint compound, about two layers, to make a hard shape, and quickly makes texture on top of it using excess drywall joint compound. Awesome. Looks much easier than the papier-mâché clay options I looked at before.

Ideas for making bark texture:

• Using an icing bag to make stripes of bark texture, like this guy did with ferrocement
• Using a roofing nail to make “valleys” for the bark texture
• Perhaps use a silicon mould with some sort of release spray to make bark texture
• Just folding the fabric into little vertical ridges

Colouring ideas:

• Dark base coat, dry brush highlight on the ridges
  • Could use dark pigment in the mix so I don’t need a base coat and damaged pieces aren’t so visible
  • Just dissolve iron oxide pigment into thick paste and dry brush that directly onto wet project?
  • Perhaps some white (TiO2) pigment to make even brighter highlights
  • Black pigment in layer mix, brown pigment in extra “ridges” mix. Or just sprinkle some on the leftover mix used for ridges and barely even mix it in for some organic variation?
• Light base coat, wet brush darker colour into ridges
  • Iron oxide brown in mix
  • Dissolve carbon black into paste and wet brush onto wet project, wipe ridges
  • Perhaps some extra dry brushed highlights

Other ideas:

• Flexible mixing container so dried gypsum is easy to remove sounds like a good idea
• Create a “folding” tree with a backing like this
  • Score the backing material (cardboard?) to allow bending?
  • Use same tulle fabric as backing material, no additional backing needed? Idea:
    • Use vaselined ground sheet, drape first layer of tulle on
    • Tape together with masking tape; tape lines are where the folds will be
    • Paint masking tape into dark colour, or just use narrow duct tape
    • Build up layers onto tulle, in between and perhaps slightly onto the tape lines
    • Whole thing should detach from groundsheet when set and should bend on tape lines
  • End product
    • 200×36 cm half round tree? (folds and stores as 100×60 cm, 4x 15 cm sides, should weigh about 4.3 kg)
    • 200×24 cm full round tree? (folds and stores as 100×80 cm, 8x 10 cm sides, should weigh about 5.7 kg)
• Alternatively, a different tree design that stores flat, e.g. two shapes that intersect like a cross when seen from above
• Alternatively, a tree design that nests for easier storage
  • Half cylinder tree trunks built using my big plastic pipe as a mould
  • More complete tree-shapes that nest like how clam shell pools nest. Would need to build a good mould to make sure they nest well
• Tree limbs
  • Form around pool noodle or piping insulation
  • Broomstick
  • Use actual branches as base
  • Rolled/scrunched up craft paper
  • Shapes out of aluminium foil

Ordered:

• Tulle fabric – 0.3×91 m
• Carbon black pigment – 1.25 kg should also last a while. Recommended to mix in at 4.8% with concrete, up to 9.1%. I don’t need very black, and gypsum probably needs less pigment than cement, so it should colour 25+ kg of gypsum
• Iron oxide brown pigment – 0.45 kg. Probably not as potent as the carbon black, might still try mixing in with the gypsum, or I could just dry brush it on as a thick paste made with just water
• Gypsum, I ordered “Gyproc Blokkenwand Stuc” which is a gypsum plaster that can also be used as a block glue, it sets in about 2.5 hours (45 minutes working time) and is suitable for thin layers up to 5mm. Sounds ideal. Comes in 10 kg, or 25 kg which only costs 19% more. However, I don’t have much space to store things, so I got the 10 kg. If it works very well I can always get a bigger one later.
• Flexible mixing vessel 25 liters

Total cost €55.57. Assuming my projects will need two 2mm layers, the gypsum will make 3m² worth of projects, the fabric and black pigment should last at least 7m².

Next up:

• Picking up ordered materials and some cardboard
• Making space and putting down plastic groundsheet
• Testing:
  • Tulle layers: 10×10 cm pieces with 2-3 layers of tulle onto vaselined cardboard. Use about 50 grams gypsum, 42.5 mL water
  • Pigment/colour: bunch of 3×3 cm pieces using 5 grams of gypsum and 4.25 mL water each, plus different amounts of pigments. Use milligram scale & weighing boats – 7 mg accuracy gives about 15% relative error at 1% pigment, I’m ok with that.
  • Texture: 30×30 cm pieces, should be about 350-500 g each
  • Folding design: 45×60 cm piece with a horizontal & two vertical folds. Should weigh about 1 kg
  • Non-flat surfaces: try on a pool noodle or something similar

To be continued.

I was looking at some compounds our lab is throwing out, saw calcium chloride and sodium sulfate, and figured those react to make gypsum. This brought me back to an old papier-mâché clay project idea I had.

Goals:

• Create 3D forms, e.g. fake tree bark / branches
• Somewhat fireproof
• Somewhat strong

Traditionally papier-mâché clay uses PVA glue, drywall joint compound (mostly gypsum) and paper to make a paste that can be shaped like regular papier-mâché but becomes much harder and stronger. I think I didn’t continue with the project before because the PVA glue got prohibitively expensive for larger projects. Now I’ve found some projects using cheaper glue, e.g. from flour/cornstarch or cooked flour. Here‘s another even simpler recipe with just flour, drywall compound and paper fibre.

Actually the first recipe is already all I need. I could add some pigment powder (e.g. iron oxide) to the mix to make it browner, so it requires less painting. This should work (video). Painting: perhaps only some darker paint in the ridges, I think using the technique in this video.

If my lab is really discarding so much calcium chloride and sodium sulfate, maybe I could make my own gypsum. However, gypsum is cheap, so it’s probably not worth it. In the interest of finishing the project, I guess I should buy drywall joint compound (snelgips). If it sets too fast, I could add a bit of citric acid (maybe 1-2% of gypsum weight) to slow the setting time.

I could use the potato starch that my lab is throwing out (expired 15 years ago), but again, starch is cheap – corn starch is like €3 per kg.

I’ll need:

• Papier-mâché clay ingredients
  • Flour
  • Cornstarch
  • Gypsum
  • Paper or cardboard – pressed cardboard apparently works well, I could save some from the lab
• Aluminium foil
• For small batches:
  • Bowls
  • Second hand hand mixer
  • Base/armature out of cardboard
• For larger batches:
  • Buckets (have)
  • Paint mixer on electric drill (have)
  • Base/armature out of PVC or wood

I could even make a tree sculpture out of the large 20cm diameter pipe that I have. Perhaps something like this. These much smaller sculptures are also very nice.

First I should make a small test batch, and also check if it is indeed fireproof!

Here‘s a recipe with just powdered joint compound and gossamer fabric instead of paper. It’s not really papier-mâché clay any more since there is no cellulose fibre, however it looks even easier, lighter, quicker to use. Hmm. Gossamer fabric is cheap (€1-2 per m, 1.4m wide),

To be continued.