Resin Casting: A Beginner's Guide to Casting Resin

Resin casting is the simple idea of pouring liquid resin into a mould and letting it harden into a solid copy of the shape. It is how makers produce crystal-clear paperweights, flowers suspended in glass-like blocks, replacement knobs, figurines, pen blanks and even the chunky resin sections in turned bowls. The basics are easy to learn, but the results depend on three decisions you make before you open a bottle: which casting resin you use, how deep you pour, and how you deal with the heat the resin gives off as it cures.

This beginner’s guide walks through the whole process, from choosing a resin by depth to embedding objects and demoulding cleanly. For an overview of mould options first, see our resin molds guide.

What is resin casting?

In resin casting, a two-part liquid (resin plus hardener, or resin plus catalyst) is mixed and poured into a mould. A chemical reaction links the molecules into a rigid solid. Unlike coating, where you spread a few millimetres over a surface, casting fills a volume, so the resin has to cure evenly right through a thick section without cracking, clouding or overheating.

That is why “casting resin” is sold as its own product category. A clear casting resin is formulated to be thinner, slower and lower in heat output than a table-top or coating epoxy, so it can be poured deeper in one go.

Choosing a casting resin by depth

The most important number on any resin label is the maximum pour depth per layer. Pour deeper than that and the reaction heat (exotherm) builds up faster than it can escape. The table below shows typical ranges; always follow the specific product’s data sheet.

Resin type	Typical max layer	Cure speed	Good for
UV resin	A few millimetres	Seconds to minutes under UV	Jewellery, thin inlays, small fixes
Coating / table-top epoxy	About 3–6 mm	Demould in roughly 24 hours	Thin castings such as coasters, layered pours
Epoxy casting resin (medium pour)	Around 1–5 cm	Demould in roughly 24–72 hours	Paperweights, pen blanks, spheres
Deep pour epoxy casting resin	Up to around 5–10 cm or more	Several days	Large blocks, river castings, turning blanks
Polyurethane casting resin	Varies; often thin sections	Minutes to hours	Opaque figures, parts, quick production

For most clear casting work, epoxy casting resin is the beginner’s best choice: it is forgiving, low in odour compared with polyester, and very clear. Our guides to clear epoxy resin and deep pour epoxy go into those products in more detail. Polyurethane resins are excellent for fast, opaque parts but are very sensitive to moisture. Polyester casting resin, the traditional choice for clear blocks, cures with a catalyst, has a strong smell and shrinks more, so it is better left until you have some experience.

Resin casting supplies: what you need

Casting resin suited to your pour depth.
A mould: silicone for most shapes (see our guide to silicone molds for resin), or a rigid mould for simple geometric blocks. Our moulds for resin casting page covers larger and deeper options.
Digital scales if your resin is mixed by weight, or graduated cups if mixed by volume. Never switch between the two.
Clean mixing cups and flat stirring sticks so you can scrape sides and base.
Nitrile gloves, eye protection and good ventilation.
A heat gun or small torch for surface bubbles.
A level, rigid board to carry and cure the mould on.
Optional: a pressure pot for bubble-free castings, pigments, and a dust cover.

A resin casting kit can bundle many of these, but check that the resin in it is genuinely a casting resin with a stated depth, rather than a thin coating epoxy.

Step-by-step: your first resin cast

Warm everything to room temperature. Most epoxy casting resins like about 20–25°C. Cold resin is thick, traps bubbles and cures slowly.
Measure the mould volume. Fill it with water, pour the water into a measuring jug, then dry the mould completely. That tells you how much resin to mix, with a little extra for waste.
Measure resin and hardener accurately to the stated ratio.
Mix slowly and thoroughly, usually for around three minutes, scraping the sides and base. Fast whipping adds bubbles; poor mixing leaves soft or sticky patches.
Add colour if wanted. Small amounts of pigment, ink or mica go a long way. See how to colour epoxy resin for ratios.
Pour low and slow into the deepest part of the mould, letting resin rise rather than splash.
Release bubbles with a quick pass of heat, or put the mould straight into a pressure pot if you use one.
Cover and leave to cure on a level surface in a stable, warm room.
Demould only after the time on the data sheet, then let the piece post-cure for several more days before sanding or polishing.

Understanding exotherm in resin casting

Every epoxy gives off heat as it cures, and in a thick casting that heat has nowhere to go. A small amount is useful, as it drives the cure. Too much and you get a runaway reaction: the resin can crack, yellow, distort the mould, smoke or create bubbles that look like boiled sugar.

To keep exotherm under control:

Respect the maximum layer depth. For deeper pieces, pour in layers, waiting until the previous layer has firmed but is still slightly tacky.
Do not leave mixed resin standing in the cup. A concentrated mass heats up much faster than the same resin spread out in a mould.
Mind the room temperature. A hot summer workshop shortens working time and increases heat build-up; a cold one slows the cure.
Mix only what you need. Large batches heat up quicker.
Watch embedded objects: big solid items such as wood or stone add mass, but also displace resin, which changes how heat behaves.

If you want the technical background, Wikipedia’s article on resin casting methods and materials covers the main resin families and how they are used in industry and hobby work.

Embedding objects in cast resin

Embedding is where resin casting gets exciting: flowers, shells, coins, insects, photographs, wood offcuts and keepsakes can all be locked inside clear resin. The rules are simple but important.

Everything must be completely dry. Moisture causes cloudiness and bubbles, and with polyurethane resin it causes foaming. Fresh flowers need drying first; see our guide to preserving flowers in resin.
Seal porous items. Paper, photos, wood and dried flowers release air and can darken when resin soaks in. Brush on a thin coat of resin or a suitable sealer and let it cure before casting.
Pour a base layer first so objects do not sit on the mould surface, where they would break through the finished face.
Stop items floating. Light objects rise. Place them in a part-cured layer, or pin them down with a small dab of resin that has started to gel.
Remember the orientation. The face against the mould bottom usually becomes the display face, so place items upside down if needed.

Demoulding and finishing

Demoulding too early is one of the most common beginner mistakes. A casting can feel hard on top but still be soft enough underneath to bend or take fingerprints. Wait the full demould time, then peel a flexible mould away from the piece rather than pushing the casting out.

Most castings need some finishing:

Trim any thin flash or a raised meniscus at the edges with a fine file or sandpaper.
Sand flat faces through progressively finer grits, working wet to control dust.
Polish back to clarity with a polishing compound. Our epoxy polishing guide covers grits and compounds step by step.
Alternatively, brush or pour a thin coat of resin over a sanded face for an instant gloss.

Safety when casting resin

Uncured epoxy is a well-known skin sensitiser: repeated contact can lead to allergic dermatitis that makes it impossible to keep working with resin. Wear nitrile gloves every time, keep resin off your skin and clothes, and work in a ventilated space. The UK Health and Safety Executive’s research report on skin sensitisation from epoxy resins explains why the reactive components cause problems and what protection helps. Sanding cured resin creates fine dust, so wear a dust mask or respirator, and sand wet where possible.

Watch it being made

Watch our first light-up resin table being made in the workshop, with dragons and creatures appearing in the resin art, and the colours, pours and finishing shown step by step.

Resin Art Dragons and creatures in resin art table My First Light-Up Resin Table. More builds on the Go Bespoke YouTube channel.

Frequently asked questions

What is the difference between casting resin and epoxy resin?

Many casting resins are epoxies, but not all epoxy is casting resin. Casting resin is thinner, slower and lower in heat output so it can be poured deeper in one layer. Coating or table-top epoxy is thicker and designed for layers of a few millimetres; poured too deep, it can overheat.

How deep can you pour clear casting resin?

It depends entirely on the product. Medium-pour casting resins typically allow a few centimetres per layer, while deep pour formulas allow much more. Check the data sheet and stay within it, pouring in layers for deeper pieces.

Why is my cast resin cloudy?

Cloudiness usually comes from moisture (damp objects or humid air), mixing too fast, a cold room, or resin that overheated. Dry embedded items thoroughly, warm the resin, mix slowly and pour within the stated depth.

Do you need a pressure pot for resin casting?

No, but it helps. A pressure pot compresses tiny bubbles until they are invisible, which is useful for detailed or very clear castings. Many beginners get good results with slow mixing, warm resin and a quick heat pass instead.

How long does cast resin take to cure?

Typically one to three days before demoulding for medium-pour epoxy casting resin, and longer for deep pours, with full hardness reached after about a week. Cooler rooms slow it down.

Want to see casting and pouring on a bigger scale? Follow our builds on the Go Bespoke YouTube channel, or move on to how two-part epoxy works for the chemistry behind every pour.

Resin Casting: Beginner’s Guide to Casting in Resin