◆ Plaster

Plaster cornice molding mold

Two 180 mm lengths of cornice with dentils, cast in plaster straight in a printed tray. Butt them into a run.

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3D render of a printed orange tray with two cornice cavities, and white plaster cornice lengths with dentils in front
Plaster ~533 g

A printed tray for two lengths of wall cornice, each 180 mm long, 70 mm tall on the wall and 40 mm deep: from the bottom up a bead, an ogee curve, a row of dentils, a flat fascia and a rounded lip that meets the ceiling. The back is flat, so it glues straight to the wall under the ceiling.

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Made with our tray mold generator in its rigid tray mode: print the tray, wipe in release and pour casting plaster straight in. Every part of the profile is cut with sloped sides, so the plaster lengths lift out of the rigid tray. The ends are square, so lengths butt into a run; cut corners with a fine saw at 45 degrees and fill the joints with plaster.

Good for a niche, a bookcase top, a fireplace surround or a short run over a doorway, and for matching a missing piece in an old room. The zip carries the tray exactly as the tool exported it, one length on its own as an STL, the master uploaded to the tool, and a print and pour sheet with the volume of each cavity.

Shown as a 3D render of the printed tray with plaster cornice lengths in front, not a photo.

Plaster cornice molding mold at a glance: every printed part with its size, print time, filament, print settings and the three steps to use it

What you need

3
  • Casting plaster or Hydrocal, about 294 ml per length
  • Mold release, petroleum jelly or cooking spray
  • Plaster adhesive or cornice cement, and a fine saw for the corners

How to cast it

4

  1. Print the tray as exported, cavities up, no supports. PLA is fine: plaster only gets warm as it sets.

  2. Wipe a thin film of mold release, petroleum jelly or cooking spray into every cavity, including the fine detail.

  3. Mix casting plaster to a pouring cream (add pigment now if you want colour), fill each cavity and tap the tray on the table for a minute to lift the bubbles.

  4. Leave it for an hour until the plaster is warm and hard, then flex the tray corners and tip the pieces out. Let them dry for a day before you add oils or paint.

Print details

17 h 50 minPrint time
~533 gFilament
1Printed parts
199 × 170 × 48 mmSize (W x D x H)
All print details
Print details
Cast materialPlaster
Printed parts1
Size (W x D x H)199 x 170 x 48 mm
Print bed needed199 x 170 mm, 48 mm tall
Filament~533 g
Layer height0.2 mm
Infill15%
SupportsNot needed
DownloadZIP: printed tray (STL) + one cornice length (STL) + tool master (STL) + print and pour sheet
Added2026-09-25
Make your own tray mold →

Made with the free Tray mold generator. Upload your own model and get the same kind of mold built around it, in your browser.

Download free on Thingiverse

Free download. Opens the Thingiverse listing in a new tab.

Free for personal use. Selling the pieces you cast needs a commercial licence (Pro or Founder); passing on the file itself is not permitted on any plan. Full terms.

New to casting? Read the ice cube tray mold guide.

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Questions about this design

How do I join lengths of the plaster cornice?

Butt the square ends together on a bed of cornice adhesive, then fill the joint with a little wet plaster and smooth it with a damp brush. For a corner, cut both lengths at 45 degrees with a fine-toothed saw once the plaster is fully dry.

Can the plaster cornice go on a real ceiling?

For a short run, yes: each length is about 350 g of plaster, light enough for cornice adhesive on a clean, primed wall. For a whole room it is quicker to buy cornice by the metre; this mold is at its best for a niche, a cabinet or a repair where you need a matching piece.

Why does the plaster cornice need release in a rigid tray?

Plaster grips a printed surface as it sets. A thin film of release, petroleum jelly or cooking spray in every cavity, including between the dentils, lets each length tip out when you flex the tray.

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