How to Clean Moulds from Uncured Epoxy Resin and Why This Happens

Resin Glory
4 days ago
3 min read

Resin crafting can be incredibly rewarding — until some molds remain sticky while others harden perfectly. In this guide, we explain why this happens and show you how to clean uncured resin so your molds are ready for your next project.

✅How to Clean Uncured Epoxy Resin From Silicone Molds

Use Isopropyl Alcohol (90–99%)
- Pour a small amount into the mold.
- Gently wipe using paper towels or a soft cloth.
- Repeat until the resin is removed.
- Wash the mold with warm soapy water and let it dry.
Use Baby Wipes
- Surprisingly effective for wiping out sticky, uncured resin.
Use Acetone (only if the mold is silicone; do not use on plastic molds)
- Apply a small amount to a cloth.
- Wipe the resin out carefully.
- Wash thoroughly afterward.
If the epoxy resin is partially cured (rubbery)
- You can often just peel it out by hand.
- Then clean the residue using isopropyl alcohol.

Important:

Avoid using harsh scrubbing tools—they can damage molds.
Make sure molds are fully dry before using them again.
If the resin isn’t curing, double-check the mix ratio (most resins require exact 1:1 or 2:1) and room temperature (should be around 21–24°C).

✅ Why Some Projects Cured and Others Didn’t

1. Incomplete or Uneven Mixing

Resin curing problems almost always come back to mixing.

If the resin and hardener aren’t thoroughly combined, some pockets will cure while others stay soft.Common mixing mistakes include:

Not scraping the sides or bottom of the mixing cup
Mixing for less than the recommended time
Pouring too quickly, leaving streaks of unmixed material

A single small streak of Part A or Part B can cause an entire cavity of a mold to never cure.

2. Temperature Differences Between Molds

Resin is extremely sensitive to temperature.Even a small difference can affect the cure.

Examples:

Molds sitting near a cold window or air-conditioning vent may stay soft.
Molds in the center of the table where it’s warmer will cure normally.
Low room temperature (below 18°C / 64°F) can stall curing entirely.

Ideal temperature for curing: 21–24°C (70–75°F).

3. Mold Depth and Volume Differences

Resin cures faster when the pour is deeper because the chemical reaction creates heat (exotherm).

Shallow molds cure slower and can even remain tacky because:

They don’t generate enough heat
They lose heat to the environment too quickly

So a deep mold may cure perfectly while a thin, shallow mold stays sticky.

4. Contamination Inside Certain Molds

Anything inside the mold can interfere with curing, including:

Soap residue
Mold release sprays
Skin oils
Water droplets
Old resin leftover

If only a few molds were contaminated, those will be the ones that stay soft.

5. Incorrect Resin Ratio

If your resin requires a 1:1 or 2:1 ratio, even a small measurement mistake can cause partial curing.

Sometimes most molds cure but one area doesn’t because the unmixed or mis-measured portion went into that specific mold cavity.

6. Humidity Issues

High humidity can slow curing and cause cloudiness or stickiness, especially with certain epoxy formulas.

🔧 How to Prevent Resin from Not Curing Next Time

Here are the most reliable ways to avoid curing issues:

✔ Mix thoroughly for 3–5 minutes, scraping the sides and bottom

✔ Keep the workspace at 21–24°C (70–75°F)

✔ Make sure molds are clean, dry, and oil-free

✔ Measure resin and hardener precisely

✔ Ensure molds aren’t too cold before pouring

✔ Avoid humidity, fans, or cold drafts during curing

📝 Final Thoughts

Uneven curing is frustrating, but it’s usually caused by one of a few predictable factors: mixing, temperature, mold condition, or resin ratio.The good news is that once you understand what went wrong, it’s easy to fix — and your molds can almost always be saved with proper cleaning.