Why is mixing epoxy resin by weight different from mixing by volume?

Epoxy resin (Part A) and hardener (Part B) have different densities. Part A typically has a specific gravity around 1.15 g/ml, while Part B is lighter at approximately 0.98 g/ml. If your epoxy specifies a 1:1 or 2:1 ratio by volume, measuring on a scale without density compensation will result in an incorrect chemical stoichiometric ratio and a sticky, improper cure.

How thick can I pour epoxy resin in a single layer?

Standard tabletop and art coating resins should not be poured deeper than 1/8 inch to 1/4 inch (3 to 6 mm) per layer because they cure quickly and produce intense heat (exothermic reaction). For deep pours like river tables or casting molds between 1 to 3 inches thick, use a slow-curing Deep Pour Casting Epoxy formulated to cure over 48 to 72 hours.

How much extra epoxy should I mix for wastage?

It is always recommended to add 10% extra epoxy. A portion of the mixed epoxy inevitably clings to the sides and bottom of mixing cups and stir sticks, and wood pores or mold crevices absorb resin during degassing.

ResinRatio Pro: Epoxy Resin & Hardener Mixing Calculator

Calculate Exact Resin & Hardener

Prevent ruined projects and sticky cures. Compute exact Part A and Part B amounts by volume or scale weight with safety thermal runaway checks.

Epoxy Supplies Explore deep pour epoxy resins, silicone coaster molds, mica pigment powders, and precision digital scales.

Project Mold Geometry

Length (in)

Width (in)

Pour Depth / Thickness (in)

Resin Chemistry & Mix Ratio

Manufacturer Mix Ratio

Overfill / Cup Residue Margin +10%

0% (Exact cavity) 10% (Recommended) 25% (High absorption)

Total Mixed Volume 393.4 fl oz (3.07 Gal)

Part A (Resin) 262.3 fl oz

Part B (Hardener) 131.1 fl oz

⚖ Digital Scale Weight Equivalence

Density: A=1.15g/ml, B=0.98g/ml

Pouring by weight on a digital kitchen or postal scale is significantly more accurate than using measuring cups.

Part A (Resin) Scale Weight 8,918 g 19.66 lbs

Part B (Hardener) Scale Weight 3,800 g 8.38 lbs

✓ Thermal Safety & Cure Assessment

Optimal Pour Profile

At a depth of 1.5 inches with a 2:1 Deep Pour casting epoxy, the slow exothermic reaction will safely dissipate heat without boiling or yellowing.

Mastering Epoxy Resin Curing Chemistry & Exothermic Heat

1. The Exothermic Reaction Explained

Epoxy resin does not "dry" through evaporation; it hardens via a thermosetting chemical cross-linking reaction between epoxide polymers and polyamine hardeners.

This reaction is exothermic (it releases thermal energy). If too much epoxy is poured into a confined cavity with low surface area, heat accelerates the cure, which creates more heat, leading to a runaway boil-over that cracks, smokes, and turns yellow.

2. Volume vs Weight Specific Gravity

Many DIY crafters accidentally cause sticky spots because they weigh epoxy on a digital scale using volume numbers:

Resin Part A: Specific Gravity ≈ 1.15 g/cm³

Hardener Part B: Specific Gravity ≈ 0.98 g/cm³

Our calculator mathematically applies these specific gravity densities so your scale readings result in perfect stoichiometric cross-linking.

Frequently Asked Questions

What room temperature is ideal for pouring epoxy? ▾

The ideal ambient temperature for curing epoxy resin is between 72°F to 78°F (22°C to 25°C) with low relative humidity (under 60%). Working in cold rooms (below 65°F / 18°C) causes micro-bubbles to get trapped due to high resin viscosity and can cause cloudiness, amine blush, or incomplete cures.

How do I seal porous live-edge wood slabs before pouring a river table? ▾

Always apply a thin "seal coat" of fast-curing 1:1 tabletop epoxy onto the raw live edges with a brush 4 to 6 hours before your main pour. This seals the wood fibers and capillaries, preventing air bubbles from continuously off-gassing into your deep river pour.

Can I fix a resin pour that turned out sticky or tacky? ▾

If tacky after 48 hours, the mix ratio or stirring was inadequate. You cannot pour another coat directly over uncured liquid. You must scrape off the sticky residue, clean the surface thoroughly with isopropyl alcohol or acetone, sand lightly, and then pour a properly measured fresh flood coat.