◆ Concrete

Spider web concrete coaster tray mold

Four spider web coasters with a spider on each, cast in concrete straight into a printed tray.

Make your own tray mold
3D render of a printed orange tray with four spider web coaster cavities, and three grey concrete coasters with an engraved web and spider in front
Concrete ~226 g Pro early access

A printed tray for four round coasters, each 96 mm across and 10 mm thick, with a spider web engraved in the face: nine spokes and five rings that sag between them like real silk, and a spider sitting on the web. A plain band runs round the edge and the face is flat, so a mug still sits level.

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Made with our tray mold generator in its rigid tray mode: print the tray, wipe in release and pour concrete, Jesmonite or plaster straight in, no silicone at all. Every groove has sloped sides, so the coaster lifts out of the rigid tray with the web crisp.

A Halloween set that can stay out all autumn: rub a black wash into the grooves so the web shows, or leave the concrete raw. The zip carries the tray exactly as the tool exported it, one coaster 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 three concrete coasters in front, not a photo.

What you need

3
  • Fine concrete or Jesmonite, about 70 ml per coaster
  • Mold release or cooking oil
  • Black acrylic paint for the web, cork pads and a sealer

How to cast it

4

  1. Print the tray as exported, cavities up, no supports. PLA is fine.

  2. Wipe a thin film of mold release or cooking oil into every cavity, including the grooves.

  3. Mix a fine concrete or Jesmonite to a thick pour, fill each cavity, and vibrate it out: tap the tray on the table or hold a sander against the side for a minute until no more bubbles rise.

  4. Cover the tray and let it cure for 24 hours, then flex the tray and tip the pieces out. Sand the back flat, and seal them once they have dried for a few days.

Print details

7 h 30 minPrint time
~226 gFilament
1Printed parts
209 × 209 × 16 mmSize (W x D x H)
All print details
Print details
Cast materialConcrete
Printed parts1
Size (W x D x H)209 x 209 x 16 mm
Print bed needed209 x 209 mm, 17 mm tall
Filament~226 g
Layer height0.2 mm
Infill15%
SupportsNot needed
DownloadZIP: printed tray (STL) + one coaster (STL) + tool master (STL) + print and pour sheet
Added2026-09-26

Pro early access until October 26, 2026, then free with any account.

Like it or post your print on Thingiverse

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.

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 make the spider web show on a concrete coaster?

Seal the coaster once and let it dry, then brush thinned black acrylic over the face and wipe the flat with a damp rag straight away. The paint stays in the grooves and the spider, and the sealer underneath stops it staining the flat. Seal again over the top.

Why did the spider web coaster stick in the printed tray?

Usually a missed spot of release in the web, the finest part of the cavity. Brush the release into every groove with a soft brush rather than wiping it on, and demold after a full day. Flex the tray corners first so air gets under the coaster before you tip it out.

Can I cast the spider web coasters in plaster?

Yes, with a strong casting plaster, and the web comes out crisp and white. Plaster is softer and marks from wet glasses, so seal the coasters well and glue cork to the back. Concrete or Jesmonite is the better pick for coasters in daily use.

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