◆ Concrete
Square concrete ashtray mold
A classic square ashtray, 100 mm with four corner rests, to cast in concrete. A silicone mold kit from printed parts.
◆ Concrete
A classic square ashtray, 100 mm with four corner rests, to cast in concrete. A silicone mold kit from printed parts.
A square concrete ashtray 100 x 100 mm and 32 mm tall, the classic shape of the heavy glass ashtrays: corners rounded to 12 mm, a square bowl 13 mm in from the rim, 20 mm deep over a 12 mm floor, and a U-shaped cigarette rest across each corner, tipped toward the bowl. Four rests means it works for a table of smokers on a terrace or a bar.
Made with the box mode of our silicone mold maker in its rectangular shape, the mode the site's mold advisor and the tool itself both suggest: the bowl would lock any rigid two-part mold. Print the base with the ashtray fused onto it, the two walls and the two clamps, and pour about 640 ml of silicone. It fills the bowl and becomes the core, and the side leans in toward the rim, so each cast slides out through its foot with no cut.
In concrete it weighs about 538 g; seal it so ash rinses off. It also makes a desk tray for paper clips, a soap dish with a drain gap at each corner, or a catch-all by the door. The zip carries every printed part, the ashtray master as its own STL, the tool's own print-settings sheet and a recipe file for the generator.
Shown as a 3D render of the printed mold parts pulled apart around the master, not a photo.
Print the base with the master fused onto it, the two walls and the two clamps.
Stand the base on the table. Set each wall down a few centimetres out from it and slide it in over the table until the ridge round the base sits in the groove at its foot, then slide the clamps down over the seams. Once they are on, the walls cannot lift, and the ridge seals the bottom.
Mix 687 ml of silicone in one batch and pour it in a thin stream down the inside of a wall, letting it rise round the master and into its well until it covers the top.
Once it has cured, take the clamps off, slide the walls straight out and pull the silicone block off the master. That block is your mold.
Turn the block over and stand it back inside the walls with the clamps on. The opening is the foot of the ashtray, with the silicone core standing up in the middle.
Mix a fine concrete or Jesmonite a little wetter than for a slab, pour it slowly down one side of the ring round the core, and tap the walls for a minute to raise the air. Fill level with the opening and strike it flat.
Leave it to cure for a day, take the walls off, peel the silicone off the outside and twist the ashtray off the core. Sand the foot flat and seal it.
Let it dry for a few days, then brush two coats of a water-based penetrating concrete sealer over the bowl and the rests, so ash and tar rinse off instead of staining.
Print details
| Cast material | Concrete |
|---|---|
| Printed parts | 5 |
| Size (W x D x H) | 128 x 128 x 70 mm |
| Print bed needed | 150 x 128 mm, 70 mm tall |
| Filament | ~347 g |
| Layer height | 0.2 mm |
| Infill | 15% |
| Supports | Not needed |
| Download | ZIP: 5 printed parts (STL) + ashtray master (STL) + print sheet + recipe |
| Added | 2026-09-26 |
Pro early access until October 26, 2026, then free with any account.
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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 silicone mold maker guide.
Each ashtray is 244 ml, about 538 g of ordinary concrete, so a 1 kg bag of rapid-set craft cement makes about three. Mix a little more than you need: topping up a pour that has started to set leaves a visible line on the foot.
Yes, once it is sealed. Tip out the rainwater that collects in the bowl, since water that freezes in unsealed concrete can flake the surface. At about 538 g it stays put in wind, which is why concrete is the usual material for balcony and terrace ashtrays.
Because that is where a cigarette lies longest across a square rim, so the ember sits well over the bowl and ash falls inside rather than on the table. Each rest is 9.5 mm wide, room for a normal or a slim cigarette, and slopes down toward the bowl.
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