# Epoxy Resin Mixing and Curing: Why Ratios and Depth Both Matter

Why a 1:1 ratio by volume is never 1:1 by weight, and how mold depth determines whether your resin cures clear or cracks from heat.

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- **Canonical URL:** https://dothecalculation.com/blog/hobby/epoxy-resin-guide
- **Category:** Hobbies & Leisure Utilities
- **Author:** Do The Calculation Team
- **Published:** 2026-08-03
- **Last updated:** 2026-08-03
- **Reading time:** 14 min read
- **Publisher:** Do The Calculation (https://dothecalculation.com)
- **Methodology:** https://dothecalculation.com/methodology

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Most epoxy resin failures — cloudy patches, a tacky surface that never fully hardens, or a deep pour that cracks from internal heat — trace back to one of two things: an imprecise mix ratio, or using the wrong resin type for the pour depth. Both are avoidable once you understand what the ratio number on a bottle actually means and why "thin coat" and "deep pour" resins are not interchangeable.

This guide covers the volume-versus-weight ratio distinction in detail, along with the heat-buildup science behind deep pours. It pairs with the [epoxy resin calculator](/calculators/epoxy-resin-calculator), which converts your mold dimensions and mix ratio directly into exact resin and hardener amounts by both volume and weight.

## Quick Answer: Ratio Numbers Mean Different Things

**Common epoxy mix ratios and what they typically mean**
| Ratio | Typical product type | What it usually specifies |
| --- | --- | --- |
| 1:1 | Tabletop / deep pour, casting resins | Usually by volume; check the data sheet |
| 2:1 | General purpose casting, some deep pour | Usually by volume |
| 3:1 or 4:1 | Some laminating and coating resins | Can be volume or weight — verify |
| 100:X (e.g., 100:47) | Industrial / technical adhesives | Always by weight |

> **The ratio on the bottle is not automatically the ratio you should measure by** — Manufacturers specify ratios either by volume or by weight, and the two numbers are almost never the same for a given product. Always check the technical data sheet before assuming — mixing a weight-ratio product by volume (or vice versa) is one of the most common causes of a resin that never fully cures.

## Why 1:1 by Volume Is Not 1:1 by Weight

Resin and hardener are different chemical formulations with different densities — resin typically sits around 1.05-1.15 g/mL, while hardener is often lighter, around 0.90-0.98 g/mL. Because a mix ratio by volume assumes equal-sized measuring containers regardless of what's inside them, a 1:1 ratio by volume routinely converts to something like a 100:83 to 100:86 ratio by weight once you account for that density difference — the two liquids simply don't weigh the same amount per milliliter.

**Volume to weight conversion**

```
Weight (g) = Volume (mL) × Density (g/mL)

Resin weight = Resin volume × Resin density
Hardener weight = Hardener volume × Hardener density
```
- Always check the product's technical data sheet for its specific density — 1.05-1.15 g/mL for resin and 0.90-0.98 g/mL for hardener are typical ranges, not universal constants.

## Two Worked Examples

**1:1 by volume, 500 mL total, resin density 1.10 g/mL, hardener density 0.95 g/mL**
| Component | Volume | Weight |
| --- | --- | --- |
| Resin | 250 mL | 275.0 g |
| Hardener | 250 mL | 237.5 g |
| Weight ratio (normalized) |  | 100 : 86.4 |

**2:1 by volume, 300 mL total, resin density 1.08 g/mL, hardener density 0.95 g/mL**
| Component | Volume | Weight |
| --- | --- | --- |
| Resin | 200 mL | 216.0 g |
| Hardener | 100 mL | 95.0 g |
| Weight ratio (normalized) |  | 100 : 44.0 |

_[Figure: Volume ratio vs. weight ratio, side by side — The hardener's share of the mix looks smaller by weight than by volume in both examples, since hardener is the lighter component.]_

In both cases, notice the weight ratio is noticeably different from the volume ratio — the 1:1 volume mix becomes roughly 100:86 by weight, and the 2:1 volume mix becomes roughly 100:44 by weight. This is completely normal and matches real manufacturer documentation; one commonly cited industrial example specifies a 100:47 weight ratio for a product sold as a 2:1 volume ratio. If you measure that same product by weight using a 2:1 ratio instead of 100:47, you'd be significantly off, and the mix could remain soft or tacky indefinitely.

Tool: [Epoxy Resin Calculator](https://dothecalculation.com/calculators/epoxy-resin-calculator) — Enter your mold dimensions, mix ratio, and component densities to get exact resin and hardener amounts by both volume and weight.

## Deep Pour vs. Thin Coat: Not Interchangeable

Epoxy cures through an exothermic chemical reaction — it generates its own heat as resin and hardener react. In a thin layer, that heat dissipates into the surrounding air fast enough to stay harmless. In a thick pour, the same reaction is trapped inside a much larger volume of curing resin with much less surface area to shed heat relative to that volume, so internal temperature can climb high enough to cause visible problems: yellowing, cloudiness, shrinkage cracks, or in extreme cases enough heat to warp or even scorch the mold.

**Thin coat vs. deep pour resin — key differences**
| Property | Thin coat / tabletop resin | Deep pour resin |
| --- | --- | --- |
| Typical max layer thickness | 1/8" (3mm) per pour | 1-2 inches (25-50mm) per pour, some formulas more |
| Cure reaction speed | Faster, more exothermic per volume | Slower, engineered to release heat gradually |
| Clarity risk if misused | Low | High — using thin-coat resin in a deep mold risks cracking or clouding |
| Typical use case | Tabletop coatings, small jewelry, coasters | River tables, large castings, thick embedments |

_[Figure: Choosing the right resin type for your pour — Depth per pour, not total project size, is the variable that determines which resin formula you need.]_

This is why river tables and other thick castings specifically call for deep-pour formulated resin rather than pouring a thin-coat product in multiple thick layers — deep-pour resins are chemically formulated to react more slowly and release heat more gradually, which is exactly what a large curing volume needs to avoid cracking. Some large projects instead pour a thin-coat resin in multiple thin layers over time (letting each layer cure before adding the next) specifically to avoid the heat-buildup problem entirely, rather than switching resin types.

## Common Failure Modes and Their Causes

- Cloudiness or a hazy finish: often caused by moisture in the mold or ambient humidity during cure, or by mixing at the wrong ratio.
- Bubbles trapped in the cured piece: usually from insufficient mixing time, pouring too fast, or not using a heat gun or torch to pop surface bubbles before the resin gels.
- A tacky or soft surface that never fully hardens: almost always an incorrect mix ratio (measured by the wrong basis — volume vs. weight — or simply measured imprecisely).
- Cracking or excessive heat in a deep pour: using a thin-coat resin at a depth it wasn't formulated for, or pouring the full depth in a single application instead of layering.
- Amber yellowing over time: normal UV degradation for many standard resins — UV-resistant or UV-stabilized formulas exist specifically for pieces that will see sunlight.

## Choosing the Right Measuring Tools

For weight-based measuring, a digital kitchen or postal scale accurate to at least 1 gram is sufficient for most hobby-scale pours — a scale that only reads in larger increments makes it hard to hit a precise ratio on smaller batches. For volume-based measuring, dedicated graduated mixing cups (not household measuring cups, which are rarely precise enough) reduce the error that compounds when scaling a ratio up to a large pour. Whichever method your product specifies, consistency in tooling matters as much as the ratio number itself — switching between two different measuring cups mid-project, for example, can introduce enough error to shift a large pour's cure quality.

## Related Tools

If your resin project sits on or inside a wooden piece, the [woodworking board foot & movement calculator](/calculators/woodworking-board-foot-movement-calculator) and [wood shrinkage & radial calculator](/calculators/wood-shrinkage-radial-calculator) help account for how the wood itself will move around your cured resin. For a finished piece that needs a painted or sealed surface instead, the [paint calculator](/calculators/paint-calculator) covers that coverage math.

## Sources to Verify or Cite

- TotalBoat, measuring epoxy by weight vs. volume: https://www.totalboat.com/blogs/totalboat/how-to-measure-epoxy-by-weight-vs-volume
- Meridian Adhesives, converting mix ratios from weight to volume: https://meridianadhesives.com/product-information-insights/how-to-convert-epoxy-mix-ratios-from-weight-to-volume/
- Your specific product's technical data sheet (TDS) for its exact density and recommended measuring method — always the authoritative source over general guidance.

## Frequently Asked Questions

**Why is my epoxy ratio 1:1 by volume but not 1:1 by weight?**

Resin and hardener are different chemical formulations with different densities. A 1:1 mix ratio by volume assumes equal-sized containers, but since resin and hardener weigh different amounts per milliliter, the same 1:1 volume mix converts to a different ratio by weight — commonly around 100:83 to 100:86.

**Can I use deep pour resin for a thin coating?**

Generally yes, though deep pour resin often cures more slowly than a dedicated thin-coat product, so it may take longer to reach full hardness for a thin surface coating. The bigger risk runs the other direction — using thin-coat resin in a deep mold.

**Why did my deep resin pour crack or turn cloudy?**

This is usually heat-related: epoxy curing is an exothermic reaction, and in a thick pour that heat can't dissipate fast enough, causing internal stress, cracking, or cloudiness. Use a resin specifically formulated for deep pours, or pour in multiple thin layers instead of one thick pour.

**How do I know if my resin ratio is by volume or by weight?**

Check the product's technical data sheet — reputable manufacturers specify both, but the primary recommended measurement method (and which scale or measuring cups to use) is listed there. Never assume; the two ratios are rarely the same number.

**My resin stayed tacky and never fully hardened — why?**

This is almost always an incorrect mix ratio, most commonly from measuring a weight-ratio product by volume (or the reverse), or from an imprecise scale/measuring tool. Double-check the data sheet's specified ratio and measurement method.

**What causes bubbles in cured epoxy?**

Insufficient mixing time, pouring too vigorously, or not degassing the surface with a heat gun or torch before the resin begins to gel. A slower, more thorough mix and a brief pass with a heat source right after pouring resolves most bubble issues.

**What is the maximum depth for a single deep pour?**

Most deep-pour formulas support 1-2 inches (25-50mm) per pour, though this varies by product — always check the specific manufacturer's maximum recommended depth per pour rather than assuming, since exceeding it risks the same heat-buildup problems as using a thin-coat resin too deep.

**Do I need a scale or can I use measuring cups?**

Either works if your product's data sheet specifies that measurement method and you use precise tools — a digital scale accurate to at least 1 gram for weight, or dedicated graduated mixing cups (not household measuring cups) for volume.

**Why does my cured resin look yellow after a few months?**

This is typically normal UV degradation for many standard epoxy formulas, especially in pieces exposed to sunlight. UV-resistant or UV-stabilized resin formulas exist specifically to slow this yellowing for pieces that will see regular sun exposure.

## Final Summary

A resin's mix ratio by volume and by weight are two different numbers, both determined by the resin and hardener's specific densities — always check the data sheet rather than assuming. Separately, match your resin formulation (thin-coat vs. deep-pour) to your actual pour depth, since heat buildup during cure is the root cause of most cracking and clouding failures in thick castings.

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_Source: [Do The Calculation](https://dothecalculation.com/blog/hobby/epoxy-resin-guide). Quote freely with attribution and a link to this page._