Dissolvable PVA Mold Maker: a one-piece mold you print, fill and dissolve

What this does

It wraps your model in a thin one-piece skin that you print in water-soluble filament, fill, and then dissolve or peel away. The skin follows the model's surface exactly on the inside and is open at the bottom. Pour in concrete, plaster, Jesmonite or resin, let it set, and remove the skin. You lose the mold, but you get a cast with no parting line, and any shape works: undercuts, overhangs, a tree full of branches, a bust with deep eyes.

Everything runs in your browser. Your model is never uploaded anywhere.

How to use it

1. Upload your model and set which way is up. The face resting on the plate becomes the opening, and the flat back of your cast.
2. Leave the wall at about 1.6 mm (two walls of a 0.8 mm nozzle, about four of a 0.4). Generate.
3. Print it in PVA or BVOH, opening down on the bed, as it comes out of the download. Dry the filament first: PVA that has taken on water strings and prints weak.
4. Turn it over, stand it in a cup of sand or rice so it sits level, and pour. Tap the sides to bring up air bubbles.
5. Wait until the cast has set (a day for most DIY concrete). Then peel the softened skin off, and soak or rinse away the rest in warm water.

Which casting materials work

Material	How it goes
DIY concrete, cement	The water in the mix softens the PVA, so after a day the skin peels off like a film. The best match for this method.
Plaster, Jesmonite	Work the same way, and set faster. Pour in one go; the skin starts to soften within the hour.
Epoxy, polyurethane resin	Water-free, so the skin stays firm and comes off in a warm water bath afterwards. Use a slow-curing resin: a fast, hot one can soften PVA from the inside.
Wax, chocolate, soap	Not a good fit. Hot wax softens PVA, and dissolving the mold in water ruins soap and chocolate. Use a two-part mold instead.

Settings

Setting	What it changes
Wall thickness	The skin's thickness at its thinnest point. Thinner dissolves faster and uses less filament; thicker holds a heavy pour without bulging.
Opening	Where the skin is cut open. At the base for anything with a flat bottom; raise it to slice a flat back onto a round model like a duck or a ball.
Rim	A flat ring around the opening. It is the first layer on the bed, it keeps the rim from flexing under the weight of the pour, and it gives you a level edge to fill to.

Common problems

The print is stringy or weak

The filament has taken on moisture. Dry PVA and BVOH before every print (a filament dryer or the oven at the temperature on the spool) and keep it in a sealed box with desiccant.

The skin bulged or leaked under the pour

Raise the wall thickness, especially on a big or heavy cast, and support the mold all round in sand. Check the print for gaps in the wall before pouring: a thin skin shows every under-extrusion.

It takes forever to dissolve

Peel first and dissolve only what is left. Warm water (40 to 60 °C) and moving water are many times faster than a still bath. BVOH dissolves faster than PVA.

The download says the model could not be wrapped

The model has holes or broken faces. Run it through the repair tool, then upload it again.

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