Marine Epoxy Mixing Ratios by Weight: 5:1, 3:1 & Cleanup Math
Dial in 5:1, 3:1, and 2:1 marine epoxy batches with weight-first math, exotherm staging tips, and calculator shortcuts for resins and hardeners.
Why weight beats volume offshore
Marine epoxy hardeners are often lighter than their companion resins. Pouring by volume can leave you several percent off ratio, especially when temperatures swing 20°F between the cabin and the dock. Switching to grams keeps the stoichiometric 5:1 or 2:1 split locked in regardless of thermal expansion.
Before your next layup, skim the MixByParts density primer to understand why SDS density data matters. Then head back here to size your marine batch with confidence.
Quick math checkpoint
A 5:1 system has six total parts. If you need a quart of finished epoxy, divide 946 mL by 6 to get 158 mL per part. Multiply by five for the resin side (â788 mL) and by resin density (1.12 g/mL) to land on ~883 g. The calculator does this instantly and lets you adjust for custom densities.
Ready-to-weigh marine epoxy tables
Pick your ratio, match the batch size, and weigh the resin and hardener targets directly. Each card links to the interactive epoxy calculator so you can tweak totals, swap units, or save the plan before you glove up.
5:1 marine laminating
Resin 1.12 g/mL, hardener 0.95 g/mL
| Total batch | Resin (mL) | Hardener (mL) | Resin (g) | Hardener (g) |
|---|---|---|---|---|
| 32 oz (946 mL) | 788 mL | 158 mL | 883 g | 150 g |
| 1 gallon (3,785 mL) | 3,154 mL | 631 mL | 3,533 g | 599 g |
| 5 liters | 4,167 mL | 833 mL | 4,667 g | 792 g |
3:1 casting & structural
Resin 1.10 g/mL, hardener 0.98 g/mL
| Total batch | Resin (mL) | Hardener (mL) | Resin (g) | Hardener (g) |
|---|---|---|---|---|
| 750 mL batch | 563 mL | 188 mL | 619 g | 184 g |
| 2 liters | 1,500 mL | 500 mL | 1,650 g | 490 g |
| 4 liters | 3,000 mL | 1,000 mL | 3,300 g | 980 g |
2:1 adhesives & fillers
Resin 1.08 g/mL, hardener 0.98 g/mL
| Total batch | Resin (mL) | Hardener (mL) | Resin (g) | Hardener (g) |
|---|---|---|---|---|
| 500 mL batch | 333 mL | 167 mL | 360 g | 163 g |
| 1 liter | 667 mL | 333 mL | 720 g | 327 g |
| 2 liters | 1,333 mL | 667 mL | 1,440 g | 653 g |
Numbers above assume 70â75°F shop temps. Cooler resin flows slowerâwarm sealed jugs in a water bath before you weigh to keep viscosity predictable.
Step-by-step mix workflow
Consistent batches are about rhythm. Use the checklist below every time you mix so your layups cure hard, fair, and bubble free.
1. Stage the workspace
Heat stubborn resins in a warm-water bath (sealed) until they pour like syrup, but stay below 90°F. Cover the bench, cue up timers, and keep silica thickener or fillers nearby if you are building fillets or fairing mixes.
2. Confirm ratio and densities
Marine epoxies span 2:1 to 5:1. Cross-check the SDS for the exact stoichiometric ratio and note the resin/hardener densities. If you are new to weight mixing, read the MixByParts primer on densities before you pour.
3. Weigh with intent
Zero the cup, add the resin target first, and re-zero. Pour hardener slowlyâthe difference between crisp cures and gummy surfaces is often a few grams. Keep paper towels and denatured alcohol handy for drips.
4. Mix and rest
Scrape the sides and bottom of the cup continuously. Most marine epoxies want two minutes of mixing and a second âinsurance cupâ pour before application. Let bubbles rise for 30â60 seconds before moving on.
5. Pour in controlled lifts
Deep pours? Split them. Stick to 3/8-inch lifts for tabletop resins and thinner passes for fairing compounds. Track each lift in the calculator so your ratio stays perfect across the job.
Already comfortable with weight-based batching? Jump straight into the epoxy calculator hub and load presets for tabletop pours, laminating runs, or structural bonding before you tape off the hull.
Control exotherm and pot life
Marine epoxies build heat fast. Exotherm spikes destroy clarity, weaken bonds, and can even smoke in the cup. Use the weight tables to split one monster batch into repeatable smaller liftsâthen track each lift in the calculator so you are never guessing mid-pour.
Exotherm minimizers
- Pour into wide, shallow trays immediately after mixing to bleed heat.
- Run fans across the layup or mold to exchange air and slow the reaction.
- Switch to slow hardener when the job stretches beyond the posted pot life.
- Stack multiple smaller batches instead of doubling a single mix beyond spec.
Batch sizing for repairs & fairing
Hull repairs, fillets, and fairing work reward small, precise batches. Use the 2:1 and 3:1 tables above as a launch pad, then adjust totals down to 150â250 mL inside the calculator for microballoon or cabosil mixes. Save each preset so repeat repairs on the same vessel take seconds to plan.
Working on brightwork or teak encapsulation? Pair these ratios with a final foam cannon rinse to strip salts and sanding dust before you lay down epoxy or varnish.
Cleanup & disposal
Wipe uncured resin with denatured alcohol, acetone, or manufacturer-approved solvents. Let cups cure before tossing them; most docks require fully hardened waste in the bin. For brushes, work solvent through the bristles, wash with warm soapy water, and hang to dry.
Label everything
Use painterâs tape or printable labels with the ratio, grams, and timestamp. That way, you can glance at the part and know whether it is still in the pot-life window or ready for the next lift.
FAQs
Can I mix marine epoxy by volume?
Only if the resin and hardener densities matchâand they rarely do. Weigh both parts so the ratio stays true in cold mornings, hot cabins, or anywhere in between.
How do I avoid exotherm in big pours?
Keep batches under the manufacturerâs recommended max, spread them thin, and use slow hardener when working in warm weather. Reuse the calculator to queue up identical follow-up pours instead of doubling a single batch.
What if the SDS density is missing?
Weigh a known volumeâlike 100 mL of resinâand divide grams by volume to back into density. Update the calculator with that value and your gram targets will snap into place.