Easy Tips for Beautiful Resin Molding and Casting

Learning how to cast resin can feel intimidating at first, but casting epoxy resin simply means pouring it into a mold so it holds that shape while it cures. Whether you're casting a river table or a pair of earrings, the basic steps are the same:

Measure the resin and hardener at the specified mix ratio.
Stir the components together slowly and thoroughly.
Add pigment, if you want color.
Pour the mix into a clean, dry, prepared mold and let it cure.

The best thing you can do before you start is to gather all your materials, so you're not hunting for a stir stick while your epoxy's working time ticks away. Below, we'll walk through how to choose the right resin, how to use resin molds, how to pour resin into molds without trapping bubbles, and how to get a flawless finish on your cured pieces.

What Is Resin Casting?

Resin casting is the process of pouring liquid two-part resin into a mold, where a chemical reaction between the resin and hardener turns it into a solid, durable piece that keeps the mold's shape and surface texture. Makers use it for everything from jewelry, coasters, and charcuterie boards to embedded keepsakes, turning blanks, and full river tables, and the same core techniques apply no matter the size of the project.

Casting Resin vs. Coating Epoxy: Choose the Right Resin for Your Project

Not every epoxy is meant for casting. Coating epoxies are thicker and designed to go on in thin layers, often ¼" or less per pour, while casting and deep pour epoxies are thinner, cure more slowly, and are formulated to be poured much deeper in a single layer. That lower viscosity also gives bubbles more time to rise and release on their own, which is a big reason deep pour formulas are the go-to for thick, crystal clear castings.

Matching the resin to the depth of your mold is the most important call you'll make. If you pour a thin coating epoxy 3" deep in one shot, the heat it generates as it cures (called exotherm) can build until it smokes, cracks, yellows, or even melts your mold and damages your work surface. Go the other direction and pour a deep pour epoxy too thin, and it may not generate enough heat to cure properly, leaving you with a soft, sticky piece that takes an eternity to set up.

Check the recommended pour depths per layer for TotalBoat resin systems before you start.

Here are a few things to consider when choosing an epoxy for your casting project:

How deep and how large will the finished piece be?
How clear do you want it to be?
Will you cure it in a pressure pot?
Will you turn it on a lathe after it cures?
How much working time do you need for color work or embedding?
Does the cure time between pours fit your schedule?

Pour depth, working time, and cure time are all listed on the product label and technical data sheet, so read them before you buy and again before you pour.

Resin Casting Supplies

Having everything within reach before you mix keeps the process calm and your results consistent. For most casting projects, you'll want:

A casting or deep pour epoxy suited to your mold depth
Silicone molds or a custom-built mold
Mold release spray or paste wax, or mold release tape for custom molds
Graduated mixing cups, stir sticks, and a clean mixing container
Epoxy-compatible colorants such as mica powders, pigment dispersions, or universal tints
A heat gun or small handheld torch for popping surface bubbles
Optional: a vacuum chamber for degassing and a pressure pot for curing
Nitrile gloves, safety glasses, and a respirator suited to your space
A silicone project mat or plastic sheeting to protect your work surface
Sandpaper and polishing compounds for finishing

Set Up Your Workspace

Choose a clean, dust-free, well-ventilated spot with a sturdy, level surface, since resin is self-leveling and will cure lopsided on a table that isn't. Cover the area with a protective silicone mat or plastic sheeting, and keep the room within the temperature range on your epoxy's label, because a cold shop slows the cure and can leave castings cloudy or soft, while a hot one shortens your working time. Wear nitrile gloves, eye protection, and long sleeves whenever you handle uncured epoxy, and for a deeper dive, check out our guide to epoxy resin safety and cleanup.

How to Use Silicone Molds for Crafts

Flexible silicone molds are the easiest place to start because epoxy doesn't bond to silicone, so cured pieces flex right out. They come in nearly every shape you can imagine, from coasters and charcuterie boards to geodes, jewelry, planters, soap dishes, trinket trays, and duck calls. A few habits will help you get the most out of them:

Match the mold's finish to the finish you want. A glossy mold surface produces a glossy casting and a dull mold produces a matte one, because the resin picks up every bit of the mold's texture.
Start clean and dry. Dust, lint, and moisture all transfer to the casting, so wipe molds out and let them dry completely before each use.
Support floppy molds. Set larger or thin-walled silicone molds on a flat, rigid board before you fill them so you can move them without flexing the mold and spilling or warping the casting.
Level the mold, not just the table. Check that the mold itself sits level so your casting cures to an even thickness.
Care for them between uses. Clean molds with mild soap and water, let them dry completely, and store them flat so they keep their shape.

Making Custom Resin Casting Molds

When no ready-made mold fits the shape or depth you need, you can build a custom mold from melamine or HDPE (high-density polyethylene), sealing the seams with silicone caulk or hot glue so the resin can't leak out. Lining the inside with sheathing tape, packing tape, or mold release tape makes it much easier to release the cured piece, especially on large river table and slab projects.

How to Use Resin Molds: Prep with Mold Release

A thin coat of mold release on a clean, dry mold creates a barrier between the casting and the mold surface, which makes demolding easier and helps extend the life of the mold, even with silicone. Aerosol spray release works best for molds with lots of fine detail because it reaches every nook and cranny, while paste wax is better suited to flat molds.

Keep in mind that the casting reflects whatever surface it cures against. Once you apply mold release, the cured piece takes on the finish of the release product rather than the mold itself, so if you want a glossy surface, choose a release agent that leaves a glossy finish.

TotalBoat Ambassador Stevie Hull spraying mold release into a prepared casting mold

Stevie Hull, of Resurgent Designs LLC, applies mold release spray to a custom mold before casting

How to Cast Resin Step by Step

1. Measure Carefully

Measure the resin and hardener at the exact mix ratio on the label. Eyeballing the ratio or adding extra hardener to speed things up is one of the most common causes of soft, sticky, or uncured castings.

2. Mix Slowly and Thoroughly

Stir the components together slowly for the full mix time on the label, scraping the sides and bottom of the container several times so no unmixed resin gets left behind. You can't avoid bubbles entirely when mixing, but slow stirring keeps them to a minimum.

3. Add Compatible Color

Epoxy won't cure properly with the wrong colorants, so stick with tints made for epoxy, such as mica powders, universal tints, and pigment dispersions, or alcohol inks. Follow the colorant's recommended percentages and start small, since too much tint can cause the cure to fail and a little goes a long way. Stir color in slowly once the resin and hardener are fully mixed.

4. Pour Resin into Molds Slowly

When you pour resin into molds, use a thin, steady stream from a low height, starting at the lowest point or deepest cavity and letting the resin spread and rise on its own. This pushes air up and out instead of trapping it, and it works the same whether you're filling a small jewelry mold or a river table form. For detailed molds, use a stir stick or toothpick to guide resin into corners and tease out bubbles hiding in recesses, and keep a spare mold or disposable cup nearby so leftover mixed epoxy can cure there instead of in the trash.

If your piece is deeper than your epoxy's maximum pour depth, pour in layers and follow the recoat window on the label before adding the next one.

Hands slowly pouring mixed epoxy into a casting mold

5. Let It Cure Undisturbed

Leave the filled mold on a level surface, loosely covered to keep dust and pet hair off the top, and resist the urge to test it with a finger. Cure time depends on the product, the depth of the pour, and the room temperature, so follow the label and give deep castings extra time before handling.

6. Demold Your Casting

Once the piece is fully cured, flex the silicone mold away from the edges and peel it back gently rather than pushing the casting out from one spot. For custom molds, remove the fasteners or break the seams and lift the walls away, then trim or sand any sharp edges before moving on to finishing.

Epoxy Resin Casting Techniques for Bubble-Free Results

Bubbles are the most common frustration in resin casting, but a few proven techniques for getting rid of bubbles will help you prevent most of them before they form and clear the rest before the epoxy sets up.

Seal Porous Objects Before Embedding

Porous items like burl wood, live edge slabs, dried flowers, seashells, and coral hold trapped air that escapes as a steady stream of tiny bubbles once they're submerged, a process known as outgassing. To prevent it, brush on a thin seal coat of mixed epoxy or dip the object in mixed epoxy, and let it cure before placing it in the mold. Spongy or punky wood like a tree burl can be stabilized by submerging it in stabilizing resin inside a vacuum chamber, which pulls the air out of the wood and replaces it with resin.

Photos and paper keepsakes like wedding invitations or trading cards need a clear sealer or a thin coat of mixed epoxy before encapsulating, and it's worth running a small test before you commit your actual mementos. Use a low-viscosity epoxy for any sealing or stabilizing work, since a deep pour epoxy won't set up properly in a thin layer.

Two images showing how porous wood has been coated in epoxy before embedding

In the examples above, porous wood and live edges are sealed with a thin coat of epoxy before being placed in the mold

Pop Surface Bubbles with a Heat Gun or Torch

After you pour, wave a heat gun on its lowest setting or a small handheld torch quickly back and forth a couple of inches above the surface. Keep it moving the whole time to avoid scorching the epoxy.

Degas with a Vacuum Chamber (Optional)

A vacuum chamber pulls bubbles out of mixed epoxy by removing air pressure, drawing them to the surface where they pop. You can degas the epoxy before pouring or degas the filled mold before it cures, but keep in mind that a vacuum chamber only removes bubbles and doesn't help the epoxy cure. Degassing TotalBoat ThickSet Fathom epoxy in a vacuum chamber

Cure in a Pressure Pot (Optional)

A pressure pot is the closest thing to a guarantee of bubble-free castings, since curing the filled mold under pressure compresses any remaining bubbles until they're no longer visible. For TotalBoat epoxies, we recommend slowly pressurizing to 45–50 psi, then releasing the pressure once the casting has fully cured.

How to Get a Flawless Finish on Your Castings

Even careful pours can leave a stray bubble, a small blemish, or a matte surface you'd rather see glossy. Protect yourself and your work surface before grinding or sanding cured epoxy, then use the fix that matches the problem.

Minor surface imperfections: Sand the cured piece lightly, remove all sanding residue, and apply a flood coat of epoxy, which cures clear and smooth over small flaws. Apply clean-release masking tape to the underside first so drips peel away easily.
Deeper imperfections: Grind out craters left by large popped bubbles with a small rotary tool, remove the dust, and fill the recess with mixed epoxy. Once it cures, sand, clean, and finish with a flood coat.
Dull surfaces: Buff and polish with TotalBuff rubbing compound followed by TotalShine finishing compound for a high-gloss shine.

For a start-to-finish look at how to embed objects in a casting and fix common problems in the cured finish, watch this in-depth video from TotalBoat Ambassador and maker extraordinaire Stevie Hull.

Troubleshooting Common Resin Casting Problems

Sticky, soft, or uncured spots: Usually caused by an off mix ratio, incomplete mixing, too much colorant, or a cold room. Uncured epoxy won't firm up with more time, so scrape out the soft material, clean the area, and repour with a fresh, carefully measured batch.
Cracks, yellowing, or smoking: A sign the epoxy got too hot, almost always from pouring deeper than the product's rated depth or curing in a hot room. Pour thinner layers or switch to a deep pour epoxy for thick castings.
Cloudy castings: Often caused by moisture, a cold workspace, or undermixed colorant, so keep molds and inclusions completely dry and work within the label's temperature range.
Casting stuck in the mold: Usually means mold release was skipped or the mold surface was damaged, so apply release before every pour, especially on rigid and custom molds.
Warping: Uneven temperatures during the cure or demolding too soon can warp thin pieces, so let castings cure fully on a level surface before handling them.

Resin Casting FAQ

How long should resin cure before I take it out of the mold?

It depends on the product, the depth of the casting, and the temperature of your space, so check the label for the demold time. Pieces can feel hard to the touch well before they reach full cure, so give thicker castings extra time and handle them gently for the first few days.

Do I need mold release for silicone molds?

Epoxy doesn't bond to silicone, so mold release isn't strictly required, but a thin coat makes demolding easier and helps your molds last longer, especially ones with fine detail. Rigid and custom-built molds should always be treated with release or lined with mold release tape.

Can I use any epoxy for casting?

Most epoxies can be cast in shallow molds, but only resins formulated for deeper pours should be used for thick castings. Pouring a coating epoxy deeper than its rated depth can cause it to overheat, crack, or yellow, so always check the maximum pour depth before you start.

How much resin do I need to fill my mold?

Multiply the length, width, and depth of your mold in inches to get its volume in cubic inches, then divide by 1.805 to convert to U.S. fluid ounces. You can also plug your measurements into the TotalBoat Epoxy Calculator and mix a little extra to account for what clings to your cups and stir sticks.

Questions? We're Here to Help

If you have any questions about casting epoxy or resin molding, call our top-notch TotalBoat Tech Support Team at (888) 986-6623 for helpful answers and guidance.