What Is a Mix Ratio?
An epoxy system is always made up of two separate components: a resin (Part A) and a hardener (Part B). These two parts must be combined in a specific proportion for the chemical cross-linking reaction — which produces the cured, solid epoxy — to complete correctly.
That specific proportion is called the mix ratio. It is expressed as two numbers separated by a colon, such as 2:1 or 1:1. The first number always refers to Part A (resin) and the second to Part B (hardener).
A 2:1 ratio by volume means: for every 2 units of resin, you add 1 unit of hardener. A 1:1 ratio means you add equal amounts of each. The ratio is not a preference you can adjust — it is determined entirely by the chemistry of the specific product.
By Volume or By Weight?
This is where many DIY applicators make costly mistakes. A mix ratio can be specified in two different ways, and they are not interchangeable:
| Measurement Type | What It Means | How to Measure |
|---|---|---|
| By Volume | Parts measured in cups, millilitres, fluid ounces, or any volumetric unit | Graduated mixing cups with clear volume markings |
| By Weight | Parts measured in grams, ounces (weight), or pounds | A digital kitchen or postal scale accurate to at least 1 gram |
Because Part A (resin) and Part B (hardener) have different densities, a 2:1 ratio by volume will produce a different proportion by weight. If your product specifies a ratio by volume, measuring by weight will give you the wrong chemical balance — and vice versa.
Your product label or Technical Data Sheet (TDS) will state clearly which measurement type applies. Never assume — always check.
Common Mix Ratios and Their Uses
Different epoxy formulations are designed with different ratios. Here are the most commonly encountered ratios and the application types they are typically associated with. This is general context only — your specific product may differ significantly.
| Mix Ratio (A:B) | Typically Found In | Notes |
|---|---|---|
| 1:1 | Tabletop coatings, bar top epoxies, some casting resins | Equal parts; easy to measure but not universal for casting |
| 2:1 | Many deep-pour casting resins, some coating systems | Two parts resin to one part hardener by volume |
| 3:1 | Some floor coatings, industrial epoxy systems | Three parts resin to one part hardener; less common in consumer products |
| 4:1 | Some specialty floor coatings and industrial formulations | Found mainly in professional application systems |
Important
This table is illustrative only. Always verify the exact ratio from your product's label or Technical Data Sheet. Ratios are not interchangeable between products, even within the same category.
How to Measure Accurately
Accurate measurement is not optional — it directly determines whether the epoxy cures correctly. Here are practical steps that apply regardless of which ratio your product uses:
- Read the label first. Confirm whether your ratio is specified by volume or by weight, and check which component goes into the mixing container first. Some products specify adding the hardener to the resin; others specify the reverse — follow your product's instruction.
- Use clean, dry containers. Any contamination — including moisture, oils, or residue from previous batches — can interfere with chemical crosslinking. Furthermore, exposure to high ambient humidity or water during curing accelerates amine blush (carbamation), an undesirable surface reaction where unreacted amine curing agents react with atmospheric moisture and carbon dioxide (CO₂) to produce a waxy, greasy film or white haze.
- Measure each component separately before combining. Measure Part A into one container and Part B into another, then combine — do not try to pour both directly into the same container while estimating by eye.
- Use a scale for precision (especially for small batches). Graduated cups can have parallax errors and are harder to read accurately at small volumes. A digital scale accurate to at least 1 gram significantly reduces measurement error — provided your ratio is specified by weight.
- Scrape the sides of each measuring container. Product left on the walls of your measuring cup means your actual mixed ratio will be off.
- Mix thoroughly for the full time specified. Scrape the sides and bottom of the mixing container during the entire mixing period. Under-mixed epoxy — even with a correct ratio — can produce soft spots and surface defects.
Worked Example
Suppose you need 1.5 litres of mixed epoxy and your product specifies a 2:1 ratio by volume.
Step-by-step calculation:
- Total parts: 2 + 1 = 3 parts
- Each part equals: 1,500 mL ÷ 3 = 500 mL per part
- Part A (resin): 2 × 500 mL = 1,000 mL
- Part B (hardener): 1 × 500 mL = 500 mL
- Total mixed: 1,000 + 500 = 1,500 mL ✓
This is a generic mathematical example. Always verify against your product's TDS.
To calculate Part A and Part B amounts for any project volume, use the Epoxy Calculator — enter your dimensions, select your mix ratio, and the calculator splits the total automatically.
What Happens If the Ratio Is Wrong?
An incorrect mix ratio means one of the reactive components is in excess. The reaction cannot fully complete, and the result is not a correctly cured epoxy film. Common signs of an off-ratio mix include:
- Sticky or tacky surface that never fully hardens, even after extended cure time
- Soft, flexible, or rubbery finished surface instead of a hard, glassy film
- Cloudy, greasy, or amine-blush surface film, especially when excess hardener leaves unreacted amine molecules at the surface to react with atmospheric humidity and CO₂
- Delamination — the epoxy fails to bond properly to the substrate or previous layers
- Accelerated yellowing over time, particularly if exposed to UV light
In most cases, improperly cured epoxy cannot be fixed by adding more hardener on top. The affected layer will typically need to be removed and the area re-coated — an expensive and time-consuming problem to correct.
Always Follow Your Manufacturer's Specification
Every detail in this guide is general in nature. Epoxy chemistry varies between manufacturers and product lines. Some products use non-standard ratios, some specify measurement by weight rather than volume, and some have additional mixing instructions that are critical to a good cure.
Your product's Technical Data Sheet (TDS) and Safety Data Sheet (SDS) are the authoritative sources for mix ratio, pot life, cure time, maximum pour depth, temperature range, and safe handling information. If in doubt, contact the manufacturer directly.