How to pick the right "deep pour epoxy."

If you have ever searched for "deep pour epoxy resin" and felt overwhelmed by the number of products claiming to be the best, you are not alone.

There is no universal deep-pour epoxy on the market. The chemistry that lets you safely pour a 3-inch river table slab is fundamentally different from what you need for a set of glass-like jewellery moulds. Using the wrong system does not just give you a suboptimal result - it can cause exothermic runaway (a dangerous overheating event), trapped micro-bubbles, or yellowing that shows up just weeks after you thought the project was finished.

Simple chemistry: what happens inside a deep pour project?

Every epoxy system is a two-part reaction. When you combine Part A (the resin) with Part B (the hardener), the molecules start linking together into a rigid three-dimensional polymer network. This cross-linking reaction releases heat - that is, the exotherm you have probably heard about.

In a thin coating layer, the heat dissipates quickly through the surface and does not cause problems. But in a thick casting? The heat has nowhere to go. It accumulates in the centre of the mass, and if the formulation is not designed for it, temperatures can climb high enough to crack the curing resin, cause discolouration, or, in extreme cases, cause the material to smoke and deform.

This is why casting resins exist as a separate category from coating resins. They are intentionally slowed down.

Three Nerpa Casting formulations - three project types.

We manufacture three casting epoxy systems at Nerpa Polymers. Each one is built around the same core principle - controlled exotherm, low viscosity, and optical clarity - but they are tuned for different project sizes, cure timelines, and performance priorities. Here is how they compare.

Casting Epoxy - the original all-rounder.

Casting Epoxy is our original deep-pour system and the product most of our customers start with. It handles layers from about 1 inch up to 2 inches at room temperature (and even thicker at cooler ambient temperatures around 17°C, where you can push closer to 2.5-3 inches per layer).

What makes this system particularly versatile is its extremely low mixed viscosity - roughly 220 centipoise at 22°C. For context, that is thinner than most cooking oils. Air bubbles rise out of the liquid almost effortlessly, which means fewer interventions with a heat gun and less risk of trapping bubbles near embedded objects like wood or dried flowers.

The working time is 5-7 hours, which gives you a comfortable window to mix, pour, position inclusions, and troubleshoot without panic. Full cure takes 7-10 days, and the resulting polymer network is impressively rigid.

This is the resin we recommend for river tables, larger sculptures, encapsulations, dioramas, and general-purpose deep pour projects where you want a reliable bio-based system with high renewable carbon content and two-stage UV protection. It is forgiving, predictable, and it has been our most popular product for good reason.

Casting Epoxy Lite - fast turnaround for thinner projects.

Not every project needs a multi-inch deep pour. If you are making coasters, jewellery, dice, small embedments, knot fills, or thin decorative layers between 0.25 and 1 inch, you do not want a slow-curing deep pour resin - you want something that reaches sanding hardness in 24-48 hours instead of sitting around for days.

That is exactly what Casting Epoxy Lite is designed to do. It uses a more reactive resin system than our original Casting Epoxy, which shortens the working time to 2–3 hours, with demolding possible in 18-30 hours. The tradeoff is a higher peak exotherm - 90°C in a 0.7 kg test mass - which is exactly why the maximum recommended layer thickness is 1 inch. In thinner sections, where the heat dissipates efficiently, you get a fast, hard cure with no issues. It is worth noting that, unlike the standard chemistry approach - use of pretty harmful catalysts, we were able to "trick" the formula to react faster without compromising your safety by the addition of these catalysts. 

An interesting detail about the Lite formulation: it actually produces a slightly harder and stiffer cured material than the original. This makes it a particularly good choice for items that might be used in warmer environments, like small functional pieces and light composite applications. 

The renewable bio-content is also the highest of the three, thanks to a viscosity reducer made entirely from bioglycerol-based molecules. Same two-stage UV protection, same crystal clarity.

Casting Epoxy Museum Grade - when clarity is everything.

Museum Grade is a different animal entirely.

The chemistry here is fundamentally different from our other two systems. Rather than relying solely on UV-absorbing additives to slow down yellowing, Casting Epoxy Museum Grade is built on a modified epoxy resin backbone that is inherently more resistant to the oxidation and photodegradation pathways that cause yellowing in the first place. Think of it this way: most epoxy systems put sunscreen on their skin, while Museum Grade was born with a naturally UV-resistant body. Both approaches help, but the inherent resistance is a fundamentally more durable strategy.

The other headline property is the refractive index, which is essentially identical to high-grade borosilicate glass. When you cast a clear piece with Museum Grade and hold it up to the light, it does not have that characteristic "plastic" look. It refracts light the way glass does. For display pieces, gallery installations, museum restorations, and high-end design objects, this is the difference you may be looking for.

To achieve these properties, the system is deliberately slow. Working time is 10–12 hours, set to touch is 60-72 hours, and full cure takes 14 days (demolding can be done in 3-4 days). The peak exotherm is remarkably gentle at only 40°C in a 1.5 kg cylinder - about half of what the original Casting Epoxy generates in the same test. This low reactivity is what allows single-pour thicknesses of up to 3 inches at room temperature and up to 4 inches in a cooler workspace.

Here is a condensed comparison to help you quickly match your project to the right product. 

A Word About Safety (What We Leave Out)

At Nerpa Polymers, we formulate without the "shortcuts" many manufacturers use to reduce costs or speed up cure times. We have made a deliberate decision to exclude:

• Nonylphenol: A well-known endocrine disruptor.

• Cresyl Glycidyl Ether: Classified as mutagenic.

• DMP-30: An accelerator that can be dangerous without industrial-grade ventilation.

Instead, we achieve our low viscosity through bio-based reactive diluents and precise chemical balancing. All our resins are compliant with Health Canada CCCR2001 regulations.

How to Decide: A Practical Guide

1. Check your layer thickness: If it's over 1 inch, skip the Lite. If it’s over 2 inches, go Museum Grade (or do multiple pours with the Original).

2. Check your timeline: Need it done by the weekend? Lite is your best friend. Can you wait two weeks for perfection? Museum Grade is the winner.

3. Pigment or Clear? If you are using heavy pigments or mica powders, the optical "glass" advantage of Museum Grade is lost. Save your budget and use the Original Casting Epoxy.

4. Consider the environment: Will the piece hold a hot coffee mug? Lite has the highest heat resistance (Tg of 52°C). Museum Grade is for display only (Tg of 38.2°C).

Common Scenarios

• "I'm building a live-edge river table.": Casting Epoxy. The classic choice for 1–2 inch pours.

• "I want to make resin coasters with flowers.": Casting Epoxy Lite. Fast cure and high heat resistance for warm mugs.

• "I'm encapsulating an object in a clear block.": Museum Grade. Unmatched long-term yellowing resistance.

• "I'm doing a museum restoration.": Museum Grade. Designed specifically for archival-quality work.

A Note on Temperature

Remember: Heat speeds up epoxy. If your workshop is 25°C+, your resin will cure faster and get hotter. If you’re pouring extra deep, try to keep your workspace closer to 17–20°C. This allows the heat to dissipate and prevents the "runaway" effect.