Ever watched those epoxy river table videos and thought "I could do that"?
I remember my first YouTube rabbit hole - hours of watching someone pour crystal-clear resin between slabs of walnut, transforming raw wood into something that belonged in a design magazine. That's when I discovered epoxy casting, and I was sold instantly.
Here's what those videos don't show: successful epoxy casting depends more on preparation than the pour itself. Miss one detail in your setup, and you're facing hardened resin on your workshop floor instead of in your mold. I learned this the expensive way. You won't have to.
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Let's walk through proper epoxy resin preparation together - the real process, including the parts where things go wrong and how to stop them before they happen.
Table of Contents
1. How Big Should Your First Epoxy Casting Project Be?
Start small. I mean it.
Your first epoxy casting project shouldn't be a dining table. Build a serving tray. Make a wood inlay. Create a small decorative piece. Get familiar with how epoxy resin behaves when the stakes are low and the material cost is under $50.
I've watched too many beginner makers jump straight to ambitious river tables, only to deal with incomplete cures, massive air bubbles, or molds that leak overnight. Those epoxy casting mistakes cost hundreds in wasted materials and days of frustration.
Master the fundamentals on small resin projects you can finish in a weekend. Scale up once you understand what you're doing.
2. Calculating How Much Epoxy Resin You'll Need
Epoxy resin is sold by weight (kilos or pounds), but you need to think in volume (liters or gallons) first. Calculate the space your mold will hold, then convert that to the weight of epoxy resin required.
Most epoxy manufacturers provide resin calculators that account for their product's specific density. Use them - they're accurate and save you from costly ordering mistakes.
Here's what catches people:
Cured epoxy resin shrinks 2-5% as it hardens. Plan for it. Order 10% more than your calculations suggest. Running short mid-pour means mixing emergency batches under time pressure, which leads to ratio mistakes and inconsistent cures.
Helpful epoxy resin calculators:
Epodex volume-to-weight calculator: https://www.epodex.com/en/media/epoxy-resin-calculator/
Brand-neutral epoxy volume calculator: https://www.omnicalculator.com/construction/epoxy
3. Choosing the Right Epoxy Resin for Your Project
Not all epoxy resins work the same. When choosing epoxy for casting, the fundamental properties that determine which product you need are:
Maximum cast thickness (how deep you can pour in one layer)
Maximum mix volume (how much you can mix at once)
Working time (how long before it starts setting)
Cure time (how long until it's fully hard)
These properties trade off against each other. Thin-layer epoxies (1-2cm depth) cure in 24 hours. Thick-pour formulas (5-10cm depth) need 72 hours. You can't cheat this ratio.
What happens if you ignore maximum casting thickness?
The mixture generates heat as it cures - that's the exothermic reaction. Pour too thick with a thin-layer formula, and the heat builds faster than it can dissipate. Within minutes, the entire batch overheats, boils, yellows, and destroys your project. I've seen it happen. The smell alone tells you it's ruined.
Exothermic reaction outcome
source: epoxyworks.com
My workshop setup: I keep both thin-layer and thick-pour epoxy on hand. They serve different purposes.
Thin-layer epoxy (up to 1cm, 24hr cure): Small projects, inlays, surface sealing, and quick turnaround work. Don't wait too long between layers - fresh epoxy bonds best to slightly tacky previous layers.
Thick-pour epoxy (up to 5cm, 72hr cure): Larger castings, river tables, deep fills. Slower cure means less heat buildup.
Try multiple brands. Cheaper products often have harsher chemical smells and inconvenient mixing ratios (like 100:45 instead of clean 2:1 ratios). It's worth paying more for formulas that are comfortable to work with.
Choose the epoxy that matches your project's requirements. Don't force a thin-layer product into a thick-pour application just because you already have it on hand.
4. Essential Epoxy Casting Setup and Preparation
Liquid epoxy resin has almost no viscosity - it flows like water and finds every imperfection in your mold. The smallest gap becomes a leak. I've walked into my workshop the morning after an epoxy pour to find most of my resin hardened on the floor instead of in the mold. It's infuriating and expensive.
Proper epoxy casting preparation matters more than the pour itself.
Set Up Your Space
Find somewhere with proper ventilation. Even food-safe certified epoxies release volatile compounds during the curing reaction. You don't want to breathe those fumes for hours. Your living room is not the place for this.
Level Your Workbench
Use a spirit level. An uneven surface means your cast won't cure flat, and you'll spend hours sanding it level later. Fix this before you pour.
Protect Your Work Surface
Cover your bench with plastic wrap or aluminum foil. Epoxy doesn't stick to polyethylene (PE) - remember that. When leaks happen (and they will, eventually), you want your bench protected.
PS: This isn't paranoia. It's learning from experience.
5. How to Make Resin Molds That Don't Leak
You have several options for resin mold materials. Each works best for specific epoxy casting project types.
Silicone Molds
Best for smaller objects and repeated castings. They're flexible, reusable, and epoxy releases from them easily.
source: totalboats.com
Polyethylene (PE) Molds
Pre-made molds from PE or HDPE plastic. Great for larger projects, fully reusable. Epoxy won't bond to them.
source: amazon.com
Plywood and melamine molds:
Cover every surface that will contact epoxy with polyethylene. Use PE plastic tape with overlapping seams at joints and corners. If seams aren't properly sealed, epoxy will seep through.Why PE plastic tape works best:
Sticks firmly to wood and melamine without peeling during the pour
Creates watertight seals at corners and joints - where most leaks happen
Removes cleanly after demolding without leaving residue
Makes your mold boards reusable
How to apply PE plastic tape:
Cover all inside surfaces that will contact resin
Overlap tape strips by at least 1 inch at seams
Press firmly to eliminate air pockets and ensure adhesion
Pay extra attention to corner joints - double-tape if needed
source: instructables.com
Critical detail: Your mold must always be deeper than the final piece height. Plan for shrinkage and leave extra depth. You can sand excess down later. You can't add height back.
6.Proper Epoxy Resin Mixing Technique
Epoxy resin comes as two components you mix just before use:
Component A: Resin
Component B: Hardener
The manufacturer specifies the exact ratio. It's not negotiable. Common ratios are 2:1 (A:B) or 1:1, but some formulas use ratios like 100:45. Follow the instructions exactly.
My Mixing Process
1. Choose the right mixing container
Don't overfill your cup - leave at least 25% empty space. This makes stirring easier and prevents spills. If your project needs more volume than one cup can handle, mix in batches and pour in layers. It's more work, but it delivers better results than struggling with an overfilled container.
2. Prepare a digital scale
For smaller projects, you need precision. Make sure your scale can handle the full weight of your mixing cup plus epoxy.
3. Weigh Component B first
I pour the hardener first. I believe it creates a more uniform mix when you add the resin on top, but honestly, this might just be superstition from my early projects. Either way, write down the exact weight.
4. Calculate and add Component A
Reset your scale, then add the precise amount of resin based on your hardener weight and the ratio. Don't eyeball this.
5. Add colorants if needed
Pigment powders or liquid tints go in now, before stirring.
6. Stir slowly for one full minute
Use a stick or spatula. Scrape the sides and bottom of your cup thoroughly - unmixed pockets will create soft spots in your cured piece. The entire mixture needs to be homogenous. Move slowly to minimize air bubbles.
7. Rest the mixture for 10-15 minutes
This lets trapped air bubbles rise to the surface and pop.
If you have access to a vacuum chamber, use it. The difference in clarity is massive, especially for transparent casts. I didn't believe this until I tried it myself - I'll never go back.
7. How to Pour Epoxy Resin Without Bubbles
Make sure any wooden components in your epoxy mold are securely fixed. You don't want them shifting once resin starts flowing around them.
source: Jeff Mack
Pour your epoxy resin slowly.
Rushing creates air bubbles. Let the resin flow naturally into the mold.
Wait for it to self-level.
Epoxy will settle and release most air bubbles on its own. Give it time.
Remove surface bubbles carefully.
Use a heat gun or small torch to pop any remaining bubbles on the surface. I prefer heat guns - they're safer and give you more control. Don't focus heat on any spot for too long, or you'll overheat the epoxy resin and cause yellowing or clouding.
Cover your mold during cure.
Dust, insects, and random workshop debris have a way of landing on wet epoxy. A simple cardboard box or plastic sheet keeps your resin casting clean.
Respect the cure time.
Don't touch it. Don't test it. Leave it alone until the manufacturer's specified epoxy cure time has passed. The viscosity will increase within a few hours, but that doesn't mean it's ready to demold. Pulling a piece too early can ruin days of work.
Congratulations on your first epoxy resin casting. 🥳
3D multicolor epoxy cast
Finished project
Processing Your Epoxy Casting Into a Finished Piece
The epoxy pour is just the beginning. Demolding, sanding, and finishing transform a rough resin casting into a professional piece.
...to be continued in Part 2: Mastering Project Processing for Perfect Results
Next in this series: We'll cover demolding, rough processing, sanding techniques, repair methods, and how to achieve that glass-smooth finish that makes epoxy projects look professional instead of homemade.
Petr
Resin Craft Guild
www.resincraftguild.com
P.S. If you're wondering whether you need a pressure pot or vacuum chamber for your first epoxy casting projects - you don't. Start with the basics in this guide, master the fundamentals of resin mixing and mold preparation, then add specialized equipment when you know exactly what problems you're trying to solve. Most beginner projects turn out great with just proper technique and patience.
Frequently Asked Questions About Epoxy Casting
What is the best epoxy resin for beginners?
Start with a thin-layer epoxy (1-2cm maximum pour depth, 24-hour cure time) for your first projects. These are more forgiving, cure faster, and cost less if mistakes happen. Popular brands include TotalBoat, ArtResin, and Stone Coat Countertops.
How do you calculate how much epoxy resin you need?
Calculate your mold's volume in liters or gallons, then use the manufacturer's calculator to convert to weight. Always order 10% more than calculated to account for 2-5% shrinkage during cure and potential mixing waste.
What causes bubbles in epoxy resin?
Bubbles form from three main sources: air trapped during mixing, air released from porous wood, and improper pouring technique. Slow stirring, sealing wood surfaces first, and letting mixed epoxy rest 10-15 minutes before pouring minimizes bubbles.
Can you pour epoxy in layers?
Yes, and often you should. Respect your epoxy's maximum pour depth - exceeding it causes overheating and project failure. For deep pours, use thick-pour epoxy formulas (up to 5-10cm per layer) or pour thin layers sequentially with proper timing between pours.
What temperature is best for epoxy casting?
Most epoxy resins cure best between 70-75°F (21-24°C). Too cold and the resin won't cure properly or takes much longer. Too hot and you risk premature curing or exothermic reaction problems, especially with thick pours.
Why won't my epoxy release from the mold?
Either you didn't use release agent on melamine molds, or you used a material that epoxy bonds to (untreated wood, unsealed plywood). Always line plywood molds with PE plastic tape or use dedicated mold materials like silicone or HDPE.
Looking to expand your resin skills? Check out these guides: