How to make resin coasters with a printed mold

The reliable way to make resin coasters with a 3D printer is to print a coaster-shaped master, cast a silicone mold from it, and pour epoxy into the silicone — epoxy grips printed plastic but releases from silicone on its own. A printed casting tray makes the silicone step easy and tells you how much silicone and resin to mix. Here's the full process, from master to finished, cured coasters.

Step 1 — Why silicone, not a printed mold

Epoxy is an adhesive: poured straight into a printed plastic mold, it locks into the layer lines and is very hard to release, even with a release agent. Silicone is the standard material for resin molds because cured epoxy peels out of it cleanly with no release agent. So the printer's job here is to make the master — the shape of the coaster — and the tray that holds the silicone around it.

Step 2 — Make the coaster master

The master is simply a coaster made of plastic, with exactly the shape and face you want the resin to have. Typical coasters are about 100–115 mm across and 6–10 mm thick.

• Plain shapes: a disc, square or hexagon STL from any CAD program or model site works.
• Personalized coasters: I made mine with the 3DGEN nameplate generator — type a short name or initials, set the Corner radius high (up to 20 mm) for a rounded-square coaster, size it with Text length, Text width and Margin to about 100 mm across, set the plate Thickness to the coaster depth, and leave the mount off. The raised letters become raised letters on every resin coaster. It takes seconds in the browser, no CAD.

Print the master with a fine layer height and smooth its face if you want glossy coasters — the silicone copies every layer line, and the resin copies the silicone.

Step 3 — Build the silicone tray

Next, open the casting tray generator and upload the master STL.

1. Choose Silicone-pour mold mode. The generator places the master inside a printed trough that holds the liquid silicone.
2. Set the grid with Columns and Rows — 2×2 gives four coasters per pour.
3. Set the trough. Trough height (over master) is the silicone above the coaster (8 mm by default); Trough wall thickness stiffens the printed walls; Trough wall draft (5° by default) slopes the walls so the cured silicone lifts out.
4. Build and read the silicone volume. Click Build tray. Once the tray is built, the Material estimate panel shows how much silicone the trough needs, in milliliters and grams — mix that much plus a little extra.

Step 4 — Pour the silicone

• Mind cure inhibition. Platinum-cure silicone can stay tacky against some printed plastics. Test a small patch first, or seal the master with a barrier coat — why silicone won't cure explains the causes and fixes.
• Mix carefully by the ratio on the silicone's datasheet, scraping the sides and bottom of the cup.
• Pour in a thin stream into one corner and let it flow over the masters — this pushes air out instead of trapping it.
• Cure fully per the datasheet, then lift the silicone out and pop the masters free. You now have a reusable silicone coaster mold.

Step 5 — Mix and pour the epoxy

1. Choose a casting or art resin — low viscosity, self-leveling and clear. Read its datasheet for mix ratio, maximum pour depth and cure times.
2. Measure exactly. Many coaster resins mix 1:1 by volume; follow your product's ratio. Mixing off-ratio is the most common reason resin stays soft.
3. Mix slowly and thoroughly — about 3–5 minutes, scraping the cup, then transfer to a clean cup and mix 2–3 minutes more.
4. Add color with resin pigments or alcohol ink, and add flowers, glitter or foil if you like.
5. Pour each cavity to the level you want. Let it rest 5–10 minutes, then pass a heat gun or torch quickly over the surface to pop bubbles.

Work in a ventilated space, wear nitrile gloves, and keep the mold level while it cures.

Step 6 — Demold and cure

• Demold once the resin is hard — commonly after at least 24 hours. Flex the silicone and push each coaster out from the back.
• Sand the edges if needed and add cork or felt pads underneath.
• Wait for the full cure — often 3–5 days at room temperature — before using the coasters.

Step 7 — Hot mugs: an honest note

Standard art epoxy is not made for high heat. A very hot mug or teapot can leave a white ring, soften the surface or distort the coaster over time, especially before the resin is fully cured. Check the heat deflection temperature on the resin's datasheet, choose a heat-resistant formulation for coasters that will see hot drinks, and wait for the full cure before first use.

Troubleshooting

• Resin stays sticky: wrong ratio, under-mixing or a cold room. Measure precisely, mix longer, and keep it warm while curing.
• Bubbles in the coaster: mix slower, warm the resin bottles before mixing, and pass a heat gun over the surface after pouring.
• The silicone didn't cure on the master: cure inhibition — seal the master or switch to a tin-cure silicone.
• Layer lines on every coaster: the silicone copied the master's surface — smooth and polish the master, then make a new mold.

FAQ

Can I pour epoxy straight into a 3D printed mold?

It usually sticks badly. Use the print as a master and cast a silicone mold — epoxy releases from silicone without any release agent.

How much silicone do I need?

The casting tray generator's Material estimate panel shows the silicone volume and weight for the tray you designed. Mix slightly more to allow for what stays in the cup.

Can I put a hot mug on a resin coaster?

Only if the resin is rated for it. Standard art epoxy can mark or soften under very hot mugs — check the datasheet's heat deflection temperature or use a heat-resistant resin.