Jesmonite® Mistakes to Avoid: How to Get the Best Results Every Time

Every creator’s been there — you mix your Jesmonite®, pour it into your mold, and… it doesn’t turn out the way you imagined. Maybe there are bubbles, cracks, or dull spots where you wanted shine. The truth is, Jesmonite® is an amazing material to work with, but it does have a few quirks.

The good news? Most Jesmonite® mistakes are totally avoidable once you know what’s going on behind the scenes. Whether you’re just getting started or perfecting your craft, here are the most common mistakes to avoid — plus easy fixes to help you create flawless, professional-looking pieces every time.

1. Skipping Accurate Measurements

Jesmonite® is all about balance. The base-to-liquid ratio isn’t just a guideline — it’s what makes your piece cure properly and feel solid.

For AC100, the correct ratio is 2.5:1 (base to liquid).

• Too much liquid = soft, chalky results.

• Too little liquid = thick, fast-setting mix that’s hard to pour.

Tip: Use a digital kitchen scale that measures in grams to weigh both parts separately— eyeballing it isn't accurate enough. Your future self (and your mold) will thank you.

2. Not Mixing Thoroughly

When Jesmonite® isn’t mixed completely, you’ll end up with uneven texture, streaks, or soft spots once it cures. Any dry clumps of base or unmixed liquid can affect color consistency and weaken your piece.

Tip: If you’re mixing by hand, use a spatula or stir stick and scrape along the sides and bottom of your container as you go. Blend until the texture is perfectly smooth — no chunks or powdery bits left behind.

For the best (and fastest) results, use a high-shear mixing blade that attaches to a drill. It ensures your Jesmonite® base and liquid combine completely, giving you a silky, even pour every time. Check out our blog on Jesmonite® tools for a full list of tools to help your creative process.

3. Taking Too Long to Mix and Pour

Jesmonite® doesn’t wait around! Once the base and liquid are combined, the working time is about 5–10 minutes — so efficient mixing is key.

Tip: Aim to mix for no more than 3–4 minutes, then pour right away for the best results. If you spend too long mixing or hesitating before you pour, the product will start to thicken and cure in your container.

If you’re coloring your project with pigments, always add your pigment to the liquid first and adjust the color until it’s perfect before adding your base powder. Trying to add pigment after the mix has been made often leads to rushed color blending and wasted time — by then, the material may already be setting.

For more detailed or layered projects that require extra working time, we strongly recommend using a Retarder. It extends your working time without compromising the integrity or strength of your finished piece.

4. Demolding Too Early or Too Late

Timing matters when it comes to demolding! If you demold too early, your piece may still be soft and fragile — making it prone to cracking, warping, or even picking up fingerprints.

But waiting too long isn’t ideal either. Jesmonite® is an exothermic material, meaning it gives off heat as it cures. If it stays in the mold for too long, it can begin to sweat as it cools, leaving behind spots or stains on your finished surface.

Tip: The ideal time to demold is right after your piece has cooled down, usually between 20–30 minutes, depending on the size and thickness of your project.

Even though it might feel solid to the touch, Jesmonite® takes about 24 hours to reach full strength. After demolding, place your pieces on a rack or tray to air cure overnight before sanding, sealing, or putting them into use.

5. Not Sealing When You Should

One of the amazing things about Jesmonite® is that it’s naturally strong, durable, and long-lasting — even without a sealer. For decorative pieces that won’t be handled often, sealing isn’t always necessary.

However, when your project will see frequent use or be exposed to water, sunlight, or outdoor conditions, sealing becomes essential. Because Jesmonite® is slightly porous, unsealed pieces can absorb moisture or develop marks over time.

Tip: Use Acrylic Matte or Gloss Sealer for a soft, satin finish that enhances color and adds water resistance.

Sealing is the final touch that keeps your Jesmonite® pieces looking beautiful — especially for coasters, trays, planters, or outdoor décor. It’s a small extra step that makes a big difference in how your projects hold up over time.

Check out this blog article which specifically breaks down sealing. 

6. Adding Too Much Pigment

Jesmonite® pigments are highly concentrated, so a little goes a long way! The general rule is to keep pigment use around 2% of your total mix weight — that’s usually plenty for bold, beautiful color.

At FTC Creative, we do our best to stick to that 2% rule — but sometimes, we want those deep, rich, solid colors that really stand out. When we go over that limit, we plan ahead.

Tip: If you exceed the 2% guideline, do so with caution and extra care. Heavier pigment loads can slightly affect how Jesmonite® cures, so:

• Handle with care during the first 24 hours — pieces may be more delicate.

• Allow extra curing time before sanding, sealing, or putting them into use.

It’s totally possible to achieve those striking, saturated tones — just plan for a little patience. With the right timing, your colors will cure strong, smooth, and stunning.

7. Working in the Wrong Environment

Jesmonite® performs best in a room-temperature, low-humidity environment (around 60–75°F / 16–24°C) — but let’s be honest, not every workspace is perfectly climate-controlled. Temperature and humidity can significantly affect curing time and surface finish, so understanding how to adapt makes all the difference.

If You’re Working in a Humid Environment:

• Humidity slows down the cure and can cause a white “bloom” or patchy surface.

• Keep your pieces in a well-ventilated space and use a fan or dehumidifier to help moisture evaporate evenly.

• Allow extra curing time before demolding or sealing.

If You’re Working in a Cold Environment:

• Jesmonite® thickens faster and may not flow as smoothly.

• Warm your base and liquid slightly to room temperature before mixing.

• You can also place molds in a warmer area (not hot!) to help them cure evenly.

If You’re Working in a Hot Environment:

• Heat speeds up curing, reducing working time and making it harder to pour smoothly.

• Mix in smaller batches and work quickly.

• For larger or more complex pours, use a Retarder to extend your working time without compromising strength.

Environmental conditions don’t have to stop you from creating — just adjust your process to match your workspace, and Jesmonite® will reward you with consistent, beautiful results every time.

8. Not Cleaning Molds Properly

One of the things creators love most about Jesmonite® is its incredible ability to capture fine detail — every texture, curve, and line shows up beautifully. But that precision works both ways: even the smallest bit of dust, leftover pigment, or debris in your mold can transfer right onto your finished piece.

What looks like a tiny speck before pouring can turn into an unwanted stain, dent, or color mark once cured.

Tip: After every use, wash your molds thoroughly with mild soap and water, then dry them completely before pouring again. Even a drop of leftover moisture can alter the finish.

Clean molds = clean results. It’s one of the simplest steps, but it makes all the difference between a flawless pour and a frustrating redo.

9. Not Tapping Out Air Bubbles

Air bubbles are part of the Jesmonite® experience — they give handmade pieces their charm and make every creation one-of-a-kind. But if your goal is a perfectly smooth, professional-looking finish, you’ll need to take a few extra steps right after pouring.

Tip: Once you’ve poured your mix, gently tap or jiggle your mold to help trapped air rise to the surface. You’ll actually see small bubbles popping as they escape — it’s oddly satisfying!

For larger or more detailed molds, consider using a vibrating plate, which shakes out bubbles evenly and saves your wrists the work.

Remember: bubbles aren’t “mistakes” — they’re a creative choice. You get to decide whether to embrace them for texture or tap them out for that flawless, polished look.

Final Thoughts

Mistakes happen — and honestly, that’s how every great maker learns. Jesmonite® is a forgiving material once you understand its rhythm. Take your time, weigh your materials, and follow the process.

With each pour, you’ll get a little closer to that perfect, smooth, bubble-free finish.

Ready to try again? Shop Jesmonite® kits, sealers, and pigments at FTC Creative and follow us on Instagram @ftc.creative for creative inspiration, behind-the-scenes tips, and more ideas for your next project.