How Much Jesmonite® Do You Need?
A Simple Guide to Calculating Material
One of the most common questions we hear from creators working with Jesmonite® is:
"How much should I mix for this project?"
Mix too little and you’re rushing to make more mid-pour.
Mix too much and you’re left with wasted material.
The good news is that calculating Jesmonite® doesn’t have to be complicated. Whether you’re casting small home décor pieces or planning a large custom project, using the right method from the start will save time, material, and frustration.
Why Getting the Amount Right Matters
Jesmonite® is a two-part system, and accuracy matters more than most people expect. When measured and mixed correctly, you’ll get:
- Strong, durable finished pieces
- Consistent color and surface finish
- Reliable curing times
- Less wasted material
When measurements are off, even slightly, it can affect how your project looks and performs.
Understanding the Jesmonite® Two-Part System
Jesmonite® is made up of two components:
- Base – the mineral powder
- Liquid – the water-based acrylic resin
These two parts are designed to work together in very specific ratios. When mixed correctly, they chemically react to create a strong, smooth, and durable material.
Each Jesmonite® product has its own ratio, which is why following the correct proportions is so important.
Jesmonite® AC100 Mixing Ratio
For Jesmonite® AC100, the ratio is: 2.5 : 1 (Base : Liquid by weight). That means for every 2.5 parts of powder, you use 1 part of liquid.
Jesmonite® should always be measured by weight, not by volume. Powder settles and compresses, which makes volume measurements unreliable. A digital scale is the best way to get consistent, repeatable results.
What Can Happen If Jesmonite® Ratios Aren't Measured Properly
Even small measurement errors can show up in your final piece.
If you use too much liquid, you may see:
- Weaker finished pieces
- Longer curing times
- Chalky or dusty surfaces
- Increased risk of cracking
If you use too much base, you may run into:
- A mix that’s too thick to pour smoothly
- Poor detail capture in the mold
- More trapped air bubbles
- Incomplete curing
Inconsistent ratios between batches can also cause color variation or visible seams, especially in layered, terrazzo, or multi-pour projects.
So let's talk about options for figuring out how much Jesmonite® you need!
For Small Craft and Home Décor Projects: Water Test + JesmoniteCalculator.com
For small craft and home décor projects, the most reliable way to calculate how much Jesmonite® you need is to use a water test with a digital scale, then plug that number into JesmoniteCalculator.com.
What you’ll need
- Your mold
- Water
- A scale that measures in grams
How to do a water test (our recommended method)
- Place your empty mold directly on the scale.
- Tare the scale to zero.
- Fill the mold completely with water.
- Record the weight shown on the scale in grams.
That number represents the approximate total water volume needed to fill your mold.
Using JesmoniteCalculator.com (Built by Razzo Studio)
Once you know your mold’s water volume, you can use JesmoniteCalculator.com to quickly calculate how much material you need.
This calculator was built by our friends at Razzo Studio and is a great tool for creators working on small-scale craft and home décor projects!
A Quick Tip From Our Experience
We recommend rounding measurements up or adding about 10% extra material to your calculation to make sure your mold fills completely, especially when using pigments or working with detailed edges.
Want to see these steps in video? Our expert maker, Maddy, walks you through it step by step in this Instagram post!
For Custom Large-Scale Projects: When a Water Test Isn’t Practical
Not every Jesmonite® project can be measured with a mold and a measuring cup.
If you’re building a custom form, casting in place, or working on a large-scale project like panels, furniture, countertops, or architectural elements, measuring water volume simply isn’t realistic.
In these cases, material planning starts with:
- Total surface area (square feet)
- Average thickness of the cast
- Whether the piece is solid, hollow, or reinforced
The goal is to translate those measurements into total material volume and then into accurate base and liquid weights.
Use the FTC Pro Calculator for Large-Scale Projects
For larger, custom projects, we recommend using the FTC Pro Calculator: https://www.ftc-pro.com/calculator.
This calculator is designed to help you:
- Convert square footage and thickness into material volume
- Calculate material needs for Jesmonite® AC730 or AC100
- Plan consistent batches before you start mixing
It’s especially useful when Jesmonite® is being used as a concrete alternative or when you need to forecast material for multi-pour projects.
A Note About FTC Pro (Our Sister Brand)
FTC Pro is our U.S.-based sister brand focused on supplying Jesmonite® in bulk quantities for industry professionals.
FTC Pro works with:
- Artists and designers
- Builders and fabricators
- Craftsmen and makers
- Architects and construction professionals
If you’re planning large-scale or professional projects, FTC Pro is set up to support Jesmonite® work at scale.
Always Add a Little Extra
No matter the size of your project, we recommend adding about 10% extra material to your calculation.
This helps account for:
- Mold or form irregularities
- Pigment absorption
- Small spills or material loss
- Minor calculator variance
Running out mid-pour is far more frustrating than having a small amount left over.
A Few Final Tips for Better Results
- Always tare your scale before measuring
- Measure base and liquid separately
- Mix thoroughly, scraping the sides and bottom of your container
- Write down quantities that work well so you can repeat them
A little planning upfront makes creating with Jesmonite® much more enjoyable.
Ready to Start Your Project?
For small craft and home décor projects, start with a water test and use:
JesmoniteCalculator.com.
For large-scale, custom, or professional projects, plan ahead with:
FTC-Pro.com/calculator.
For more tips, tutorials, and creative inspiration, follow us on Instagram @ftc.creative. We’re here to help creators feel confident working with Jesmonite®, from first pour to final finish.
